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Sleep Training Truths: What Science Can (And Can't) Tell Us About Crying It Out

Michaeleen Doucleff

Welcome to parenthood! For many of us, parenthood is like being air-dropped into a foreign land, where protohumans rule and communication is performed through cryptic screams and colorful fluids. And to top it off, in this new world, sleep is like gold: precious and rare. (Oh, so precious.)

Throughout human history, children were typically raised in large, extended families filled with aunts, uncles, grannies, grandpas and siblings. Adding another baby to the mix didn't really make a big dent.

Nowadays, though, many moms and dads are going about it alone. As a result, taking care of a newborn can be relentless. There are too few arms for rocking, too few chests for sleeping and too few hours in the day to stream The Great British Bake Off . At some point, many parents need the baby to sleep — alone and quietly — for a few hours.

And so, out of self-preservation, many of us turn to the common, albeit controversial, practice of sleep training, in hopes of coaxing the baby to sleep by herself. Some parents swear by it. They say it's the only way they and their babies got any sleep. Others parents say letting a baby cry is harmful.

What does the science say? Here we try to separate fiction from fact and offer a few reassuring tips for wary parents. Let's start with the basics.

Myth: Sleep training is synonymous with the "cry-it-out" method.

Fact: Researchers today are investigating a wide range of gentler sleep training approaches that can help.

The mommy blogs and parenting books often mix up sleep training with "cry it out," says Jodi Mindell , a psychologist at Children's Hospital of Philadelphia who has helped thousands of babies and parents get more sleep over the past 20 years. In fact, most of the time, it's not that.

"I think unfortunately sleep training has gotten a really bad rap because it's been equated with this moniker called 'cry it out,' " Mindell says.

Indeed, the cry-it-out approach does sound cruel to many parents. "You put your baby into their crib or their room, you close the door and you don't come back till the next day," Mindell says. "But that's not the reality of what we recommend or what parents typically do."

And it's not what scientists have been studying over the past 20 years. Cry-it-out is an old way of thinking, says Mindell, author of one of the most frequently cited studies on sleep training (and the popular book Sleeping Through The Night ).

In today's scientific literature, the term "sleep training" is an umbrella term that refers to a spectrum of approaches to help babies learn to fall asleep by themselves. It includes much gentler methods than cry-it-out or the so-called Ferber method . For example, some sleep training starts off by having the parent sleep next to the baby's crib (a method called camping out) or simply involves educating parents about baby sleep.

"All these methods are lumped together in the scientific literature as 'sleep training,' " Mindell says.

In several studies, parents are taught a very gentle approach to sleep training. They are told to place the baby in the crib and then soothe him — by patting or rubbing his back — until he stops crying. The parent then leaves the room. If the baby begins crying, the parent is supposed to check in after waiting some amount of time. In one study , these types of gentle interventions reduced the percentage of parents reporting sleep problems five months later by about 30%.

Myth: There's a "right" amount of time to let your baby cry when you're trying to sleep train.

Fact: There's not a strict formula that works for every parent (or baby).

There isn't a magic number of minutes that works best for checking on a baby after you've put her down, Mindell says. It really depends on what parents feel comfortable with.

"Doesn't matter if you come back and check on the baby every 30 seconds or whether you come back every five minutes," she says. "If it's your first child you're going in every 20 seconds." But by the third, she jokes, 10 minutes of crying may not seem like a lot.

There is no scientific data showing that checking every three minutes or every 10 minutes is going to work faster or better than checking more often. There are about a dozen or so high-quality studies on sleep training. Each study tests a slightly different approach. And none really compares different methods. In many studies, multiple methods are combined. For example, parents are taught both how to sleep train and how to set up a good bedtime routine. So it's impossible to say one approach works better than the other, especially for every baby, Mindell says.

Instead of looking for a strict formula — such as checking every five minutes — parents should focus on finding what Mindell calls "the magic moment" — that is, the moment when the child can fall asleep independently without the parent in the room. For some children, more soothing or more check-ins may help bring forth the magic, and for other babies, less soothing, fewer check-ins may work better.

With my daughter, I finally figured out that one type of crying meant she needed some TLC, but another meant she wanted to be left alone.

Even having a good bedtime routine can make a difference. "I think education is key," Mindell says. "One study I just reviewed found that when new parents learn about how babies sleep, their newborns are more likely to be better sleepers at 3 and 6 months."

"So you just have figure out what works best for you, your family and the baby's temperament," she says.

Myth: It's not real sleep training if you don't hear tons of crying.

Fact: Gentler approaches work, too. And sometimes nothing works.

You don't have to hear tons of crying if you don't want, Mindell says.

The scientific literature suggests all the gentler approaches — such as camping out and parental education — can help most babies and parents get more sleep, at least for a few months. In 2006, Mindell reviewed 52 studies on various sleep training methods. And in 49 of the studies, sleep training decreased resistance to sleep at bedtime and night wakings, as reported by the parents.

There's a popular belief that "cry it out" is the fastest way to teach babies to sleep independently. But there's no evidence that's true, Mindell says.

"Parents are looking for like what's the most effective method," Mindell says. "But what that is depends on the parents and the baby. It's a personalized formula. There's no question about it."

And if nothing seems to work, don't push too hard. For about 20% of babies, sleep training just doesn't work, Mindell says.

"Your child may not be ready for sleep training, for whatever reason," she says. "Maybe they're too young, or they're going through separation anxiety, or there may be an underlying medical issue, such as reflux."

Myth: Once I sleep train my baby, I can expect her to sleep through the night, every night.

Fact: Most sleep training techniques help some parents, for some time, but they don't always stick.

Don't expect a miracle from any sleep training method, especially when it comes to long-term results.

None of the sleep training studies are large enough — or quantitative enough — to tell parents how much better a baby will sleep or how much less often that baby will wake up after trying a method, or how long the changes will last.

"I think that idea is a made-up fantasy," Mindell says. "It would be great if we could say exactly how much improvement you're going to see in your child, but any improvement is good. "

Even the old studies on cry-it-out warned readers that breakthrough crying sometimes occurred at night and that retraining was likely needed after a few months.

The vast majority of sleep training studies don't actually measure how much a baby sleeps or wakes up. But instead, they rely on parent reports to measure sleep improvements, which can be biased. For example, one of the high-quality studies found that a gentle sleep training method reduced the probability of parents reporting sleep problems by about 30% in their 1-year-old. But by the time those kids were 2 years old, the effect disappeared .

Another recent study found two kinds of sleep training helped babies sleep better — for a few months. It tried to compare two sleep training approaches: one where the parent gradually allows the baby to cry for longer periods of time and one where the parent shifts the baby's bedtime to a later time (the time he naturally falls asleep), and then the parent slowly moves the time up to the desired bedtime. The data suggest that both methods reduced the time it takes for a baby to fall asleep at night and the number of times the baby wakes up at night.

But the study was quite small, just 43 infants. And the size of the effects varied greatly among the babies. So it's hard to say how much improvement is expected. After both methods, babies were still waking up, on average, one to two times a night, three months later.

Bottom line, don't expect a miracle, especially when it comes to long-term results. Even if the training has worked for your baby, the effect will likely wear off, you might be back to square one, and some parents choose to redo the training.

Myth: Sleep training (or NOT sleep training) my children could harm them in the long term.

Fact: There's no data to show either choice hurts your child in the long-run.

Some parents worry sleep training could be harmful long-term. Or that not doing it could set up their kids for problems later on.

The science doesn't support either of these fears, says Dr. Harriet Hiscock , a pediatrician at the Royal Children's Hospital in Melbourne, Australia, who has authored some of the best studies on the topic.

In particular, Hiscock led one of the few long-term studies on the topic. It's a randomized controlled trial — the gold standard in medical science — with more than 200 families. Blogs and parenting books often cite the study as "proof" that the cry-it-out method doesn't harm children. But if you look closely, you quickly see that the study doesn't actually test "cry it out." Instead, it tests two other gentler methods, including the camping out method.

"It's not shut the door on the child and leave," Hiscock says.

In the study , families were either taught a gentle sleep training method or given regular pediatric care. Then Hiscock and colleagues checked up on the families five years later to see if the sleep training had any detrimental effects on the children's emotional health or their relationship with their parents. The researchers also measured the children's stress levels and accessed their sleep habits.

In the end, Hiscock and her colleagues couldn't find any long-term difference between the children who had been sleep trained as babies and those who hadn't. "We concluded that there were no harmful effects on children's behavior, sleep, or the parent-child relationship," Hiscock says.

In other words, the gentle sleep training didn't make a lick of difference — bad or good — by the time kids reached about age 6. For this reason, Hiscock says parents shouldn't feel pressure to sleep train, or not to sleep train a baby. "I just think it's really important to not make parents feel guilty about their choice [on sleep training]," Hiscock says. "We need to show them scientific evidence, and then let them make up their own minds."

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Does Sleep Training Your Baby Cause Long Term Harm?

Here’s what you need to know about the latest research on sleep training.

Almost every exhausted new parent has wondered about the pros and cons of sleeping training their baby. Will it work? What method should I use? And the big question: Will it cause harm? While it’s still unclear which method will work best for each baby and family, mounting research suggests that the practice of letting a baby cry for short intervals while learning to put herself to sleep is not inherently harmful —and does not seem to cause long term emotional problems for the baby or disrupt the parent-child bond. However, there are some caveats, explains Kimberly Schneider, M.D. pediatrician at Indiana University Health. Here’s what you need to know about the latest research on sleep training.

In a recent study published in the journal Pediatrics , researchers evaluated 43 sets of parents and babies in Australia. In one group, the parents didn’t follow a particular sleep training method, and instead were given basic sleep information. In a second group, parents used a method called bedtime fading in which they delayed bedtime by prescribed increments each night to land on a time for sleep when their babies were tired enough to doze off easily. (Some proponents of the bedtime fading method also say it’s key to keep a consistent wake time.) A third group followed a method called graduated extinction, which involves letting the baby cry for a short interval, then coming back to check on the baby, and then increasing the intervals between check ins. This is done over several nights.

When the researchers measured the stress levels of the babies by analyzing their saliva for the stress hormone cortisol, the babies in the sleep training groups showed slightly lower cortisol levels than the babies who had no sleep training. This suggests that in the bedtime fading group and the graduated extinction group, the babies had less stress and anxiety. What’s more, the babies that did follow a sleep training method feel asleep more quickly and woke up less frequently in the middle of the night.

The results were positive 12 months later as well. The study authors found that after a year, there was no difference among the groups in the children’s emotional and behavioral health or in the parent-child attachment. “It is an encouraging study and should help parents feel less guilt about sleep training,” says Dr. Schneider. “Though the study is too small to say definitely that there are no long term consequences to the crying, it supports what pediatricians have thought for a long time.”

It’s important to point out, though, that graduated extinction, which is often called “crying it out,” does not mean that you simply let your baby cry indefinitely. “It’s a misconception that ‘crying it out’ means you don’t ever go in and check on your baby,” says Dr. Schneider. “You should not leave a baby in the nursery crying for hours, and not check to be sure he is okay.” This can cause severe stress and could be unsafe as well. “With graduated extinction, you’re letting your baby know with each check in: ‘I’m still here, do you really need me?’” adds Dr. Schneider. “If you see your baby is okay, you let her know you’re going to leave again.”

So what should parents take away from the latest research? “Parents have to decide for themselves if and how much they can listen to their baby cry, but this study suggests that as long as you are there, persistently and gently guiding the way, it’s okay to let your baby cry for short periods of time as he learns to self soothe and put himself to sleep,” says Dr. Schneider. Once he masters that skill, he’ll be able to fall asleep more easily at bedtime and put himself back to sleep when he wakes in the middle of the night. This can, of course, minimize sleepless nights and improve overall wellbeing for babies and parents.

Before you start a sleep training plan, Dr. Schneider recommends that you check with your pediatrician to make sure that your baby is healthy, growing well, and able to skip nighttime feedings. “This usually happens when a baby is around 6 months,” she says. It’s also important to develop a consistent bedtime routine (such as a bath, book, and lullaby) that your baby learns to associate with getting drowsy and going to sleep. Also, keep the room dark for sleep and naps, which will cue your baby that it’s sleep time.  

Finally, one of the best things you can do to set the stage for sleep training, says Dr. Schneider, is to lay your baby down for sleep when she is drowsy but awake, from the very beginning of her life. “That way, your baby learns early on that she doesn’t need you to put her to sleep,” says Dr. Schneider.

-- By Rachel Rabkin Peachman

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What Does Science REALLY Say About Sleep Training?

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My Exhausted Year in Instagram’s Anti–Sleep Training Rabbit Hole

I still don’t know who’s correct about “cry it out.”.

In late September, professional sleep consultant Chrissy Lawler, known by the Instagram handle the.peaceful.sleeper , livestreamed herself sleep training an infant named Charlotte. According to the posts, the baby—newly 5 months old, but born five weeks early—belonged to a longtime friend, who had taken the rest of her family to Disneyland for the weekend. In the videos, Lawler uses a version of the Ferber method: putting the baby down to cry in a crib for lengthening intervals, before returning to reassure her. Between the check-ins, the camera zooms in on the baby monitor, which shows Charlotte splayed and wailing in a crib that we’re told has been set up in Lawler’s toy closet. “24 minutes of protest night one,” went one update. “Not bad for learning a skill that will benefit her forever. Protest is uncomfortable but it is part of growth and it is worth it!”

These stories captured the attention of the growing anti–sleep training movement active on Instagram. Even parents who didn’t necessarily have a problem with sleep training were perturbed by this episode, the details of which accumulated into something that felt villainous: a very young baby, separated from her family, crying alone in a space not her own, her anguish captured for a wide audience as a kind of advertisement. (“We can tailor a plan to you and your babe to get great sleep,” Lawler interjects midtraining, with a link to her consultations, the most intensive of which start at $499.)

When I finally watched the video, I was surprised by my own reaction. I had seen a lot of anti–sleep training videos on Instagram by then. Yet, strangely, after consuming so much content about the horrors of “cry it out,” in watching Lawler’s video I found myself more weirded out than horrified. Lawler’s peppy enthusiasm for the task was bizarre, and her use of the euphemisms protesting and sleep learning felt like clever, if spurious, rebranding. But the baby’s recorded cries, which I played on the lowest volume so as not to attract my own child’s attention, did not incite in me the same world-ending feelings of doom that his do. Of course, it was not my child, and I wasn’t there. That’s why, after all, Charlotte’s parents had let someone else do this for them (or perhaps paid her to do so).

Right after my child was born, my Instagram feed, responding to my browsing, was overtaken by posts about baby sleep. Blond women, not unlike Lawler, doled out commands about schedules and swaddles while a mysterious, if fetching, lump dozed on my lap. This was a time of effortless newborn slumber that I would quickly come to miss. Soon, my baby was waking every couple of hours, a habit he continued for most of his first year.

A wakeful baby is a tale as old as time, but a parent up at night with a glowing world of information at their fingertips isn’t. Once confined to child-rearing books and unsolicited remarks from relatives, sleep advice has become a lucrative business. Recently, at the Cut, Laura Hazard Owen, whose kids are a bit older, delved into the world of TikTok sleep advice. I think it’s fair to say that Owen’s piece tilts toward the pro-training side of the dial. She spoke with several authors of sleep-training manuals as well as to parents who’d sleep trained (those she quotes are well rested, happy) and those who hadn’t (tired, and sleeping in uncomfortable configurations). I’m here not to make a wholly anti-training argument—I’m still not entirely sure what I think—but rather to explain how anti-training accounts spoke to me in the middle of the night, when everyone else was asleep, except for me and my baby.

And it’s not just me. The social media scene that seemed like foreign terrain to Owen was just the water where the parents I interviewed about social media sleep advice this past summer were swimming. Like me, they were mothers in their 30s who’d had their first child in the past couple of years and were finding information on Instagram—what Owen calls “the social network for old millennials” (that’s me)—where sleep specialists (a designation that is not regulated) offer free content as a portal to paid courses, guides, and coaching services.

As with many phenomena located in the place where parenting philosophies and social media overlap, there is little middle ground: On one side are the specialists who say you must sleep train your baby or face a lifetime of sleep disturbance; on the other is the “gentle” or “holistic” camp, who argue that leaving a child to cry themselves to sleep shouldn’t be a rite of passage. As my baby grew and my own REM sleep receded into memory, I began to feel that this fight was a microcosm of American parenthood. Faced with a profound lack of social support, parents became fixated on the choices within their control, creating a rigid ideology around them. In the absence of help, sleep, or mental health, you could at least have the solace of knowing you were right.

The ubiquity of sleep training in parenting advice for infants can make it seem as natural as cooing at a newborn, as necessary as a diaper change. “Join me in loudly singing the praises of good old cry-it-out!” went an essay on Romper , an endorsement that might seem gratuitous when CIO, in mom group parlance, and its variants are routinely recommended by pediatricians, and a recent survey found that 63 percent of American parents had tried sleep training (only 23 percent didn’t plan to). None of the Instagram accounts that oppose the practice— HeySleepyBaby is the biggest, with a following that approximates Lawler’s, but there’s also IslaGraceSleep , Sarah Ockwell-Smith , Resting_in_Motherhood (formerly known as Lilahby Sleep), and Kaitlin Klimmer —have the audience of celebrity sleep trainers like Taking Cara Babies (2.2 million), but they are a growing voice in parenting circles. Rarely is a sleep question posted in a mom group these days without a commenter making a referral to HSB in reply.

What makes wading through the sleep-training discourse challenging—besides lack of sleep itself—is that the relevant research is not terribly good. Helen Ball, director of the Durham Infancy and Sleep Centre in the U.K., received so many questions from parents and providers in search of solid info that she started a website to summarize her findings. Though she believes that the research is improving, Ball said that until the past decade, most studies looked at parental perception of babies’ sleep; this is different from studying what physiologically or neurologically happens to a baby during the night. In the sleep-training chapter of her popular book Cribsheet , for example, much-read economist and parenting writer Emily Oster cites research that suggests that “babies seem happier after sleep training than before.” But that happiness is parent-reported—a 4-month-old can’t fill out a survey—as is evidence of longer stretches of sleep. Ball noted that more recent studies that use ActiGraphs (wearable sensors, similar to Fitbits, that capture movement to suggest patterns of wakefulness) rather than parental reporting tend to show that “sleep-trained” babies don’t really “sleep better,” they just wake their parents less. This is a good illustration of how little clarity the research provides. Sleep trainers say that when parents stop responding to cries, babies put themselves back to sleep. Opponents of the practice deem this not self-soothing but the end of signaling; having learned that their cries go unanswered, babies still wake but stop reaching out. To one group, this is a feature; to the other, a bug.

Studies have not shown that sleep training damages babies in the short or long term, and it’s unlikely a study could ever decisively prove such harm. As with research on other parenting decisions—breastfeeding, school choices, almost everything —it’s impossible to separate out the effects on children of the innumerable factors that lead parents to make certain decisions from the effects of the decisions themselves. Still, sleep-training opponents counter that the absence of evidence is not the same as the absence of harm and that the wide body of research on attachment can be extrapolated from to assume that sleep training has negative effects. I’m sympathetic to this inclination: It can feel as if, because an infant’s mental health is difficult to discern—let alone study—it is assumed not to exist or matter, and plenty of history’s cold-seeming child-rearing advice has been predicated on the idea that it doesn’t. But ultimately, I suspect that whom you choose to believe about sleep training may simply come down to which of the keywords from this debate, as they filter down to social media, strike more of a chord with you: “randomized trial” and “methodologies,” for instance, or “co-regulation” and “nurture.”

“They’re just trying to sell you something!” is a popular refrain on the anti-training pages, which refute the idea that the wakeful baby is a problem to be solved. Of course, they also have offerings for sale: HSB, for instance, sells courses ($24–$89) and consultation packages (up to $529). (Instead of CIO, they advise on crib transfers, changing sleep associations, tweaking schedules, and sometimes co-sleeping.) But there is some truth to their claims that sleep training is a market-driven solution to a modern problem. As the scholar Cecília Tomori has written , infant sleep wasn’t mentioned in baby manuals at all until the mid-19 th century. The sleep advice genre emerged as people migrated away from their families, taking on factory and office work in urban settings, and a continuous night of parental sleep became more critical. The term cry it out famously comes from an 1894 manual by Dr. L. Emmett Holt that claimed, “At five months a child should not be fed or nursed between 10 P.M. and 6 A.M.” Though some of Holt’s other advice has fallen out of favor—he also warned against kissing babies for fear of spreading disease—his claims that night feeds are detrimental past a certain age and that with each night of crying a child will learn to cry less are still basic tenets of sleep training.

Online opponents of the practice take sleep training’s history as discrediting. A post by one of the more extreme anti-training Instagram accounts, @nurture_neuroscience_parenting , shows four white men—Drs. Holt, Spock, Ferber, and Weissbluth—with a long caption proclaiming: “The doctors pictured above founded sleep training and withholding nurture from babies.” While to advocates a child’s crying in service of sleep is like getting skinned knees while learning to ride a bike—“I can think of several things that involve 24 minutes of protest that do not permanently damage your relationship with your baby!” claimed Lawler in her Charlotte stories—the anti-training “specialists” argue that CIO is harmful to babies’ (and, secondarily, parents’) mental health. In one story, HSB said, “With what we know about attachment and the infant brain, sleep training is likely not IDEAL for most.” Others are less measured: “Teaching children doesn’t happen via fear and separation,” wrote Kaitlin Klimmer.

New to the morass of parenting social media, I initially found such stridency appealing. It stood in contrast to the placating but unserious “do you , Mama” vibe of many momfluencers. By naming parenting decisions as ethical ones, these accounts endowed care work with meaning; rousing repeatedly to pacify a wailing baby was awful, but calling what you were doing responsiveness made it righteous. When even the AAP handouts given at well-baby visits contain sleep-training advice—instructing parents to “check on, but do not pick up the baby, if she cries at night” (though also, confusingly, to “help your baby when she needs it”)—this defiance of the mainstream felt radical. Or at least as radical as anything marketed on Instagram to desperate, sleep-deprived parents can be.

My child slept like a baby: poorly, then worse. In his first months, we cycled through strategies and setups—bassinet, co-sleeping, crib, various routines, and an army of sleep associations—and though he sometimes “protested,” as Lawler might put it, we didn’t leave him alone to cry, a line that seemed both random and essential. My feed thrummed with contradictory strategies: Follow cues, nurse to sleep, respond, repeat. Others said to deposit the baby in his crib at appointed times “drowsy but awake”—a state I’d rarely achieved myself—and not to pick him up when he woke. For a long time, the most expedient and only reliable strategy for getting him to go to sleep was to nurse him until his eyes closed, which is what I did.

According to the sleep trainers, this approach meant my baby would never learn to sleep. But the holistic camp assured me his wakefulness was by design, and that sleep is a biological function that can’t be taught. According to a BBC deep dive on the science of baby sleep shared widely by these accounts last winter, babies wake regularly as protection against SIDS; their frequent nursing, a necessity for newborn stomachs, also builds supply for nursing parents. Sleep varies wildly between babies and throughout the first year: One study found that at 6 months babies woke between zero and 15 times per night, and by 8 months some woke even more. But by age 2, studies show, there’s no difference between sleep-trained and non–sleep trained kids’ sleep, making this a question of short-term strategy—except that each day, let alone each year, is an eternity if you’re sleep-deprived.

Because so many parents sleep train as early as 4 months—a time frame I suspect has as much to do with the outer limit of parental leave as with the end of the newborn phase—it can be incredibly isolating to still be up with a baby every few hours, months beyond that. One of the benefits of a discourse on infant sleep that goes beyond “cry it out,” parents I spoke with told me, is a reality check on what that sleep actually looks like: Your baby isn’t broken if they’re waking often; they’re just a baby. “I think this whole concept of ‘normalizing infant sleep’ is fairly recent,” a parent named Kara told me, “and I’m grateful to have access to these resources. I might have done the same things anyway, but I might have had more anxiety about them or guilt that I was doing something wrong.”

Other parents told me they started out following anti–sleep training accounts, intending to take their prescribed approach, but eventually sleep trained anyway. None of them regretted it, and afterward, they could see how the anti–sleep training messaging in their feeds exacerbated their suffering. One of them, Helen, said, “I think equating ‘normal’ infant sleep with acceptable infant sleep,” as these accounts do, “is, in present day, in a country without paid leave and without affordable child care, ultimately not going to resonate with many parents.” Another parent, Kristen, saw these accounts as “preying on women when they’re most vulnerable, sleep-deprived, and unsure of themselves.” But, she said, even though she was confident in her choice, “the mom accounts f—ed with my head and made me feel bad about using ‘cry it out’ methods.”

To these parents, baby sleep seemed fraught, maybe even political, in a way it hadn’t for their friends who, like Laura Hazard Owen, had kids earlier in the social media era and sleep trained them without much angst. But the parenting pendulum swings fast on social media. Now, “gentle” and “respectful” parenting tips dominate, and philosophies that suggest asking your pre-verbal child’s consent for each diaper change seem incompatible with leaving them to cry at night. (Interestingly, Janet Lansbury, the grande dame of “respectful parenting,” is not opposed to sleep training.) The Instagram advice industry, which rewards more decisive and provocative posts over ambiguity or indifference, has loomed large for those of us who became parents during the pandemic, consigned to Zoom parenting classes and unable to find IRL camaraderie. Social media offers something that can feel like community but is actually the monetization of agreement. No one craves validation like a new parent; it feels the same, even if it’s an algorithm ferreting out consensus to keep you scrolling.

The intensity with which people sought sleep advice derived not only from desperation but also from a drive for “evidence-based” decision-making. Maybe we had the popularity of Emily Oster to blame for new parents moonlighting as researchers. It wasn’t enough to do what feels right, or even to do what your own parents did: Every choice must be backed by data. This quest for evidence about a topic for which the research is inconclusive often leaves parents more confused. The “gentle” accounts periodically have to assure followers that a baby fussing in their car seat while the parent drives, unable to soothe them, isn’t on par with CIO. People wonder if anything sleep trainers suggest—basics like a bedtime routine or white noise—is a harmful intervention. And both proponents and opponents of sleep training appeal to new parents’ lack of confidence. For every parent like me who despaired over the sleep-training messaging that responding to a baby’s cries would create “bad habits,” there’s a parent whose extreme worry around separation or their child’s experiencing any distress—concerns that can indicate postpartum anxiety —gets validated by the messaging of sleep-training opponents.

I found something perturbing, and distinctly American, about staunch sleep-training advocates: their dogma of independence, aversion to empathizing with the helpless (no eye contact with newborns at bedtime!), the equating of crying with manipulation and extending care with overindulgence. But the anti–sleep training accounts seemed to embody the other extreme: the expectation of self-sacrifice in a system of paltry support, the spinning of your suffering into some saccharine story ( they won’t be babies forever! ), a belief in the supremacy of the baby’s well-being over that of the caretaker, usually a mother, that failed to acknowledge the sheer interdependence of early parenting. Did this really help people get any rest?

Babies may be designed to wake frequently, but adults are not, and after six months of sleep deprivation, I’d begun to fantasize about walking through our apartment’s giant windows. I’d once enjoyed the light that streamed in, but now it only marked the arrival of another thankless day. What was a day when you never slept more than three hours at a stretch? Maternal mental health is often cited as a reason to sleep train, and surely mine was suffering. Yet I found myself, despite my depletion, increasingly disgruntled by the sleep advice I could locate.

While the holistic accounts have a progressive posture, in reality what they propose—keeping babies near, following rhythms, not schedules—is traditional, the norm for most of human history. Yet this glorification of the past didn’t sit right with me. A post by Resting_in_Motherhood evoked old images of mothers carrying sleeping babies on their backs while they worked, with the text: “Mothers of the past (and many mothers today all over the world) didn’t stress about the perfect nap.” This may be true, but in most other ways, I would prefer to be a mother with 21 st -century amenities. Though this global mother was often alluded to in the anti-training accounts I followed—independent baby sleep is not the norm worldwide—these accounts are run primarily by, and presumably for, Westerners, and they trend white.

Kara, who appreciated these accounts, told me she nonetheless thought a lot about what she called the “unbearable whiteness” of the anti-training movement, which reminded her of “other things, like baby-led weaning” (the practice of feeding babies small amounts of adult food, rather than specialized purees) or “drinking while breastfeeding, that get considered lazy, neglectful, passive, indulgent, or selfish when anyone other than rich white women do it.” But another interviewee, Helen, found these accounts’ appeal to the “traditional” unpersuasive: “I think it’s OK that in America we’ve adapted parenting styles that suit our cultural context,” she said.

Not to mention that all the “normalizing” in the world didn’t seem to dispel parents’ fixation with their child’s sleep, linked as it was to their own sleep deprivation. The HSB Facebook group was awash in posts from people seeking, through iron testing, floor beds, and the right wake windows, to crack the code of sleep without resorting to CIO. These accounts’ oft-used term biologically normal , to describe how infants sleep without intervention, was off-putting to me. Vulnerability to disease and injury is also normal in babies, but most of us correct for that by vaccinating and using car seats. The sweeping inferences about attachment sometimes felt like a boogeyman, and the anxiety over avoiding harm produced philosophical inconsistencies among the anti-trainers: HSB had an entire guide on transferring your sleeping infant to a crib, but Sarah Ockwell-Smith suggested that such maneuvers were “unsettling.”

As my parental confidence grew, I began to suspect I’d gravitated to these accounts not because I found their evidence superior but simply because they affirmed an instinct I already had, which was quite personal: The period during which we might be able to meet all of our child’s needs was terribly short; why cut it shorter? My husband and I both had early memories—positive ones, for us—of retreating to our parents’ beds. On a level I wanted to think was ethical but may have been straightforwardly emotional, we weren’t convinced our availability should end at bedtime. Although we pretended to wrestle with the choice—I was not the kind of beneficent mother who “soaked up the snuggles” and assured myself this was just “a season”—I see now that my ambivalence precluded sleep training, which to be effective requires a consistency predicated on the conviction that it’s correct.

At around 10 months, more exhausted than ever, we moved our baby to his own room, and he immediately began sleeping for longer stretches, sometimes through the night. (When he was born, the AAP recommended room sharing until 12 months; this advice was recently revised down to 6.) Knowing he could do this, even when he didn’t, put to rest our lingering anxiety about our choices. The antis were right: You didn’t need to “teach” a baby to sleep! But it was also true that my first year of motherhood had been irrevocably marked by an exhaustion that sometimes bled into suicidal ideation.

Helen had told me that prior to trying Ferber, she’d agonized about the idea of following a sleep trainer’s advice, until she registered that the anti–sleep trainers were also strangers telling her what to do with her baby. I’d had a similar revelation. Maybe this was a moment all new parents had: the realization that, whatever edicts issued from your screen or doctor or friends, you were the closest thing to an expert on your child that there was going to be.

A couple of weeks before baby Charlotte was made Instagram infamous, the anti–sleep training camp scored a major public relations win. Author and doctor Gabor Maté went on Joe Rogan’s extremely popular podcast and, in the opening minutes of a lengthy interview, decried CIO. The topic of the conversation, and of Maté’s newest book, was the sources of toxicity in our culture, one of which Maté identifies as our child-rearing mores. “We actually tell parents not to pick up the kids when they’re crying,” he said, which “has an impact on the child’s trust in the world, sense of safety, sense of belonging, and how they feel about themselves.”

Maté doesn’t use the term sleep training in the interview, but he does talk about Ferber in a blog post from 2017 in which he said he regretted using the method on his own children and recommending it as a family physician. He had come to believe, through reading “neuropsychological research” (he doesn’t cite specific work), that the practice was harmful, and that just because a young baby wouldn’t have “narrative memories” of being sleep trained didn’t mean the experience wouldn’t imprint on them. “The implicit message an infant receives from having her cries ignored is that the world—as represented by her caregivers—is indifferent to her feelings,” he wrote.

If the gentle camp, with the help of people like Maté, gets its way, it may succeed in positioning sleep training as something like spanking: a parenting practice, once ubiquitous, that time, research, and changing sentiment eventually made unfashionable (which is not the same thing as a practice’s being eradicated). The histories of child rearing and pediatrics are indeed full of practices later widely understood to have been ineffective or even harmful. Holt, the grandfather of sleep training, also advised against feeding salads to anyone under age 10. The effects of sleep training are harder to study than those of disciplinary tactics, and whereas practicing gentle discipline instead of spanking shouldn’t significantly negatively impact parents beyond requiring a mental paradigm shift and different strategies for handling problems, the sleep deprivation you may face by eschewing training makes a serious mark. And even if sleep training is, as some suggest, an unfortunate byproduct of capitalism, a world in which parents have adequate support to survive prolonged sleep deprivation doesn’t appear in sight.

It might be true that CIO is no big deal, as Lawler suggests; it may also be true that one day we’ll learn that the body does, in fact, “keep the score” in the way Maté describes. Very plausibly, this depends on the baby, its caregivers, and the particular circumstances of each family unit, particularities for which blanket advice makes little allowance. Recently, some holistic sleep accounts have allowed that sleep training is OK in “extreme circumstances.” What exactly those circumstances are—would my old fantasy of walking through the windows, while I was still ultimately able to care for my child, qualify?—isn’t specified, creating more questions than answers. You can find this kind of lack of clarity across the sleep advice landscape: see, on the other “side,” the perplexed questions in mom groups from parents whose sleep-trained infants have become sleep-resistant toddlers.

The parents I talked to who opted not to sleep train were not the fringe crunchies of TikTok who believe that cribs are prisons; they were interested in gentle parenting and how the small and large ways we regard our children when they’re little might have an effect on the people they become. This was a worldview shared by the parents I talked to who sleep trained, for whom better nights allowed them to be better parents by day.

My child is now teetering into toddlerhood, at an age and level of cognition when leaving him to cry at night seems genuinely cruel, not to mention pointless. He sometimes sleeps great, and at other times our nights are derailed by teething, illness, or the vagaries of a rapidly developing brain. I despair for sleep when it’s scarce, of course, but as my child is more visibly his own person, my anxiety about my role in creating whomever he becomes recedes a little. Instead of seeking perfect, data-backed, harm-proof choices at every step, I endeavor to remember that try as we might, most people do not remain eternally unscathed. My own mother, of whom I have only glowing childhood memories, was by all accounts responsive, bed-shared for years, and nursed me forever, yet I nonetheless became an adult with a vast profile of neuroses. If it’s not your handling of sleep that messes up your kid, it’ll be something else. These days, it’s that, more than anything else, that helps me sleep.

Does Sleep Training Actually Improve Infants' Sleep?

A summary of the research on the effectiveness of sleep training..

Posted September 21, 2023 | Reviewed by Michelle Quirk

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• Sleep training may result in modest improvements in at least parent-reported sleep for children over 6 months.
• Sleep training is unlikely to result in long-term improvements in sleep.
• Most research on sleep training uses parent-report measures, which may be inaccurate or biased.

In the intense debate over sleep training, even parenting books offer conflicting advice, with about two-thirds advising parents to use sleep training and one-third advising against it. But what does the research actually say? Is sleep training effective?

Research broadly finds that sleep training methods improve sleep for infants according to parent report, yet it is unclear whether they actually improve sleep according to objective measures of actual sleep time. A 2006 review study found that 82 percent of children show clinically significant improvement in sleep with sleep training. However, most of these studies (77 percent) used parent-report measures, which may be biased or inaccurate.

Randomized Controlled Trials of Sleep Training

Fortunately, we have a few randomized controlled trials that use objective measures of sleep, called actigraphy (translation: data from monitors that the infants wear that show whether or not they wake up). One randomized controlled trial of sleep training with 6- to 8-month-olds who had a parent-reported “sleep problem” randomly assigned parents to get instruction on infant sleep or safety. The instructions on infant sleep involved a description of the "checking in" method but also other important information such as the importance of having a bedtime routine. Interestingly, the researchers found that, although parents reported that their babies were waking up less frequently, sleep actigraphy found that the babies in the sleep-training group were waking up just as often. However, the actigraphy found that sleep-trained babies slept longer for their first period before waking—yet, on average, only 16 minutes longer.

After the intervention, 4 percent of the sleep-training group reported their child still had a sleep problem, while 14 percent of the control group did. The parents who received instruction on sleep training also reported improved mood, sleep quality, and fatigue.

This study had some important limitations. Although the intervention group received information about sleep training, it is unclear whether they actually followed these instructions, and researchers did not determine whether any parents in the control group used sleep training. It is also unclear whether it was the sleep training or learning other important sleep information such as bedtime routines that resulted in slightly longer sleep times.

Another randomized controlled trial assigned parents to one of three groups: (1) checking in, (2) bedtime fading, or (3) sleep education . The researchers found that both children in the "checking in" and "bedtime fading" groups slept better after treatment according to parent report but found no differences according to objective measures of sleep.

Although parent report may be biased, these data are still important because it may mean that the parents were sleeping better. There did not seem to be a significant difference in the sleep training group at the end of the intervention for wake after sleep onset, number of awakenings, or total sleep time. Sleep training also did not result in infants “sleeping through the night.” However, the lack of differences among groups may have been because some percentage of parents in the intervention groups did not use the sleep-training methods advised by researchers, and some percentage of the "sleep education" group might have used sleep training even when they were not advised to do so.

A question commonly asked with sleep training methods is whether they lead to any long-lasting changes. One randomized controlled trial followed children for 5 years and focused only on 8- to 10-month-olds with reported “sleep problems.” They allowed mothers to choose either the "checking in" or "camping out" method and taught parents how to use the strategy of their choice as well as positive sleep strategies, such as bedtime routines.

The first report of this study found that mothers were less likely to report their child still had a sleep problem by 10 and 12 months. Yet, 56 percent of mothers at 10 months and 39 percent of mothers at 12 months still reported a sleep problem even after sleep training. A follow-up study found that the difference between the intervention and control groups faded by age two. In the final follow-up study at 6 years , the researchers found no difference in sleep between the two groups, including whether parents reported sleep problems or differences in children’s sleep habits. These findings suggest that the benefits of sleep training may be temporary and not necessary for a child to develop independent sleep skills.

It is very important to mention that we do not have sufficient evidence that sleep training is effective before 6 months. One of the only randomized trials of young infants found no impact of educating parents about infant sleep before 12 weeks. Another larger randomized controlled trial of educating parents about infant sleep before 6 months found that the intervention only decreased night awakening by 8 percent and that the babies only slept for 6 minutes longer during the day.

Translation

Sleep training may provide moderate sleep improvements but is unlikely to result in long-term improvements in sleep or guarantee a child will be a “good sleeper” as a toddler or a preschooler. Two randomized controlled trials suggest that sleep training increases the first stretch of sleep by about 15 minutes when compared to a control group. Some parents may conclude that parent-reported improvements in sleep and the possibility of 15 minutes of extra sleep for their baby is very significant to their quality of life and decide to attempt sleep training. However, other parents may conclude that sleep training may not be worth it without consistent evidence for objective and long-lasting improvements in sleep.

Cara Goodwin, Ph.D., is a licensed clinical psychologist who specializes in translating scientific research into information that is useful, accurate, and relevant for parents.

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Follow-up patients and procedures, sample size and analyses, conclusions, acknowledgments, five-year follow-up of harms and benefits of behavioral infant sleep intervention: randomized trial.

FINANCIAL DISCLOSURE: All authors had financial support from the Foundation for Children for the submitted work (see Funding, below); no financial relationships with any organizations that might have an interest in the submitted work in the previous 3 years; no other relationships or activities that could appear to have influenced the submitted work.

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Anna M.H. Price , Melissa Wake , Obioha C. Ukoumunne , Harriet Hiscock; Five-Year Follow-up of Harms and Benefits of Behavioral Infant Sleep Intervention: Randomized Trial. Pediatrics October 2012; 130 (4): 643–651. 10.1542/peds.2011-3467

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Randomized trials have demonstrated the short- to medium-term effectiveness of behavioral infant sleep interventions. However, concerns persist that they may harm children’s emotional development and subsequent mental health. This study aimed to determine long-term harms and/or benefits of an infant behavioral sleep program at age 6 years on (1) child, (2) child-parent, and (3) maternal outcomes.

Three hundred twenty-six children (173 intervention) with parent-reported sleep problems at age 7 months were selected from a population sample of 692 infants recruited from well-child centers. The study was a 5-year follow-up of a population-based cluster-randomized trial. Allocation was concealed and researchers (but not parents) were blinded to group allocation. Behavioral techniques were delivered over 1 to 3 individual nurse consultations at infant age 8 to 10 months, versus usual care. The main outcomes measured were (1) child mental health, sleep, psychosocial functioning, stress regulation; (2) child-parent relationship; and (3) maternal mental health and parenting styles.

Two hundred twenty-five families (69%) participated. There was no evidence of differences between intervention and control families for any outcome, including (1) children’s emotional ( P = .8) and conduct behavior scores ( P = .6), sleep problems (9% vs 7%, P = .2), sleep habits score ( P = .4), parent- ( P = .7) and child-reported ( P = .8) psychosocial functioning, chronic stress (29% vs 22%, P = .4); (2) child-parent closeness ( P = .1) and conflict ( P = .4), global relationship ( P = .9), disinhibited attachment ( P = .3); and (3) parent depression, anxiety, and stress scores ( P = .9) or authoritative parenting (63% vs 59%, P = .5).

Behavioral sleep techniques have no marked long-lasting effects (positive or negative). Parents and health professionals can confidently use these techniques to reduce the short- to medium-term burden of infant sleep problems and maternal depression.

Behavioral techniques effectively reduce infant sleep problems and associated maternal depression in the short- to medium-term (4–16 months’ postintervention). Despite their effectiveness, theoretical concerns persist about long-term harm on children’s emotional development, stress regulation, mental health, and the child-parent relationship.

Behavioral sleep techniques did not cause long-lasting harms or benefits to child, child-parent, or maternal outcomes. Parents and health professionals can feel comfortable about using these techniques to reduce the population burden of infant sleep problems and maternal depression.

Infant sleep problems are prevalent, reported by up to 45% of mothers in the second 6 months of life, and double the risk of maternal depression symptoms. 1 , 2 As a common driver of health care use during infancy, they are also costly for families and health systems. 3 Fortunately, they are often readily treatable. From 6 months of age, extinction-derived behavioral techniques like “controlled comforting” (see D1 in Guide for Fig 1 ) help infants learn to self-settle and sleep independently. 4 , 5  

Graphical depiction (“Perera diagram” 30 ) of the components of the trial shared and unique to the intervention and control groups. MCH, maternal and child health.

Mindell et al’s 2006 systematic review of behavioral interventions for child sleep problems found that 49 of 52 programs led to clinically significant reductions in bedtime resistance and night waking 3 to 6 months later. 4 Secondary benefits included better parent sleep, mental health, and child-parent relationships. No studies, including the longest follow-up to date (3 years’ postintervention), 6 have reported detrimental effects. 3 , 4 , 7 , 8 The American Academy of Sleep Medicine subsequently classified behavioral techniques as “standard” practice for managing infant sleep problems, 9 and a recent expert working party convened by the Australian Research Alliance for Children and Youth concluded that behavioral approaches are safe, at least in the short term. 10  

Despite strong evidence of the short- and medium-term benefit and cost-effectiveness of behavioral sleep techniques, unproved concerns about their long-term harm are limiting their uptake and provoking vigorous debate. For example, a 2011 review by Blunden et al 11 notes that behavioral techniques could prevent parents from responding consistently and sensitively to their child, thereby leading to long-term adverse impacts on child-parent bonding, child stress regulation, mental health, and emotional development. These concerns originated with pure extinction (“crying-it-out”), which is not usually recommended nowadays because of the distress it causes parents and infants. However, the concerns have extended to extinction derivatives like controlled comforting and “camping out,” 11 which are recommended for best practice. 4 , 9 In response to Blunden et al, 11 Sadeh et al 12 countered that there is no evidence that behavioral techniques cause harm. Researchers from these opposing perspectives are calling for a rigorous longitudinal study of the long-term effects of behavioral sleep interventions to resolve this controversy. 11 , 12  

Interestingly, this debate is largely framed around possible harms rather than the potential for lasting benefits. In the absence of long-term follow-up studies, it is entirely possible that benefits to maternal mental health may extend beyond the medium-term already demonstrated. 7 Furthermore, teaching parents to regulate their children’s sleep behavior is a form of limit setting that, combined with parental warmth, constitutes the optimal, authoritative, parenting style for child outcomes. 13 , 14  

In 2003–2005, Hiscock and colleagues 3 conducted the Infant Sleep Study. Designed to improve Australian infants’ sleep problems at 8 to 10 months of age, it was a large, community-based, secondary-prevention randomized trial of a behavioral intervention comprising positive bedtime routines and teaching either controlled comforting or adult fading (also known as camping out), should parents choose to use them. In comparison with controls, intervention parents reported fewer sleep problems at infant age 10 months (56% [intervention] vs 68% [control]; adjusted odds ratio [aOR] 0.6 [95% confidence interval 0.4–0.9]) and 12 months (39% vs 55%; aOR 0.5 [0.3–0.8]), 3 with a sustained reduction in maternal depression at 2 years (15% vs 26%; aOR 0.4 [0.2–0.9]). 7  

To determine long-term harms and/or benefits of this infant behavioral sleep intervention, we now report our 2009 follow-up at age 6 years. We hypothesized that there would be no evidence of intervention versus control group differences in: (1) child emotional and conduct behavior (primary outcomes), sleep, psychosocial health-related quality of life, and diurnal cortisol as a marker of stress; (2) child-parent relationship, disinhibited attachment; or (3) maternal mental health or parenting styles.

The Kids Sleep Study is the 5-year follow-up of the Infant Sleep Study, a randomized controlled trial (International Standard Randomized Controlled Trial Number 48752250) for which we have previously reported methods for outcomes at ages 12 3 and 24 7 months. In brief, the Infant Sleep Study aimed to recruit all mothers with children born in June to July 2003 who attended the free, universal 4-month well-child check with their maternal and child health nurse in 6 sociodemographically diverse local government areas ( n = 982). Of these, 782 (80%) expressed interest in participating; 692 (70%) returned the 7-month questionnaire. Mothers who responded “Yes” to the 7-month screening questionnaire item “Over the last 2 weeks, has your baby’s sleep generally been a problem for you?” were eligible for the trial ( n = 328, 47%). Maternal and child health nurses excluded infants born <32 weeks’ gestation and mothers with insufficient English to complete questionnaires.

After baseline recruitment, we randomized the 49 maternal and child health nurse centers (clusters) which, in turn, determined participant allocation. 3 Because nurses were responsible for delivering the intervention, randomizing clusters rather than participating families minimized the likelihood of contamination between trial arms. Centers were ranked within each stratum according to the number of infants recruited at 4 months, randomizing the largest center and alternately allocating subsequent ones to avoid a marked imbalance in cluster sizes between trial arms. Because all the centers were recruited before randomization and ranked by using a criterion that could not be influenced by the investigators, allocation concealment was achieved. Researchers involved in data collection and entry were blinded; nurses and parents, however, could not be blinded to group allocation.

Intervention nurses were trained to deliver a brief, standardized behavioral sleep intervention at the routine 8-month well-child check to mothers reporting infant sleep problems ( Fig 1 and Guide show details). Based on their needs and preferences, each family chose which (if any) type or mix of strategies they would use to try and manage their infant’s sleep. 3 One hundred of the 174 intervention mothers attended their nurse well-child check visits to discuss infant sleep problem management for an average of 1.52 visits, with mean duration for the first and subsequent visits of 25 and 19 minutes, respectively. Control families received usual care, which meant they were free to attend the scheduled 8-month visit and ask for sleep advice; control nurses, however, were not trained to deliver specific sleep management techniques.

From April to October 2009, we recontacted all families. Of the original 328 Infant Sleep Study children, 3 326 were eligible at age 6, whereas 2 met our prespecified exclusion criteria of intellectual disability or developmental delay ( Fig 2 ). Parents who returned written informed consent were mailed a questionnaire and phoned to arrange a 40- to 60-minute home-based assessment as close as practicable to the child’s sixth birthday, during which the trained researchers (1) administered the Pediatric Quality of Life Inventory 15 to the child and (2) showed families how to collect salivary cortisol (see Table 1 ).

Participant flow for the original Infant Sleep Study to 6-year-old outcomes. All clusters were trained (so 0 “did not receive intervention”), but not all individuals received the intervention. †Take-up of the intervention was voluntary. One hundred families reported receiving the intervention. *All lost to follow-up because of failure to return questionnaires. ‡Did not return the 10- or 12-month follow-up questionnaire (were not sent 2-year questionnaire). §Did not return 2-year follow-up questionnaire. MCH, maternal and child health.

Families selected a nonschool day (weekend or holiday) to collect 2 cortisol samples: (1) 30 to 40 minutes after waking to avoid the postawakening rise, because its meaning in relation to the diurnal cortisol profile or psychosocial stress is unclear, 16 and (2) before lunch. We based our collection protocol on the standardized procedures provided by the pathology laboratories responsible for testing samples. Children avoided brushing teeth, eating or drinking for 30 minutes before collection, then thoroughly rinsed their mouth with water 3 times, chewed a piece of Wrigley’s sugarfree gum, EXTRA peppermint, and collected 4 mL of saliva in a plain tube. Families recorded children’s waking and saliva collection times. Families stored samples at room temperature before mailing them back within 1 to 2 weeks of collection, 17 when we froze them at −18°C. Cortisol levels were measured by 2 local laboratories owing to an unexpected company merger (by using the Roche Modular and Avida Centaur systems, respectively). Interassay coefficients of variation fell below 5.3% ( n = 113 samples) and 15% ( n = 54) for the 2 laboratories, respectively. No saliva-based intraassay reliabilities were available. The proportion of intervention samples analyzed by each laboratory was similar (55% vs 46%, respectively).

Table 1 shows details of the outcome measures. For all variables but cortisol, we selected potential confounding variables a priori based on existing research. 18 Throughout childhood, child gender, temperament, maternal depression, and socioeconomic status (maternal education and Socioeconomic Indexes for Areas 19 Index of Relative Disadvantage) are associated with and predict most outcomes examined in the Kids Sleep Study. 1 , 20 Socio-Economic Indexes for Areas is a national index derived from census data for all individuals living in a postal code, with higher scores indicating less disadvantage. We controlled for all 5 potential confounders in the adjusted analyses, except some analyses of binary outcomes in which the sample size was too small to include all 5 without causing instability in the resulting estimates 21 (see “Sample Size and Analyses” below). For Strengths and Difficulties Questionnaire (SDQ) continuous scores, we additionally adjusted for financial stress (6-point quantitative item, “Given your current needs and financial responsibilities, how would you say you and your family are getting on?”; responses range from “prosperous” to “very poor”), because Longitudinal Study of Australian Children data indicate that financial stresses are associated with a doubling of the risk of behavior problems in 2- to 7-year-olds. 22 In the absence of a strong conceptual framework for choosing cortisol confounders, we used exploratory analyses to identify variables associated with “abnormal” cortisol levels at P < .1. 18 This applied to the laboratory at which testing occurred only.

6-Year-Old Outcome Measures; Parent Report Unless Otherwise Specified

The original Infant Sleep Study was powered to detect a difference of 20% between the proportions of mothers reporting infant sleep problems at each of the 10- and 12-month follow-ups with 80% power at the 5% level of significance, with an assumed cluster size of 11 and intracluster correlation coefficient of 0.02. 3 For the Kids Sleep Study follow-up (not considered at the original sample size calculation), we anticipated retaining at least 75% of the 2-year-old participants (99 of 132 control and 110 of 146 intervention families, total n = 209). A sample size of 99 per group would give the study 80% power to detect a difference of 0.4 SD units (ie, effect size) between groups at the 5% level of significance. We did not allow for intracluster correlation, because we expected any cluster effects to fade over the 5 years since the intervention.

We compared trial arms by fitting random effects linear regression models estimated by using maximum likelihood for quantitative outcomes, and marginal logistic regression models by using generalized estimating equations, assuming an exchangeable correlation structure with information sandwich (“robust”) estimates of SE for binary outcomes. 23 Both methods allow for correlation between outcomes of participants from the same cluster. We conducted analyses unadjusted and adjusted for the potential confounders, with the exception of analyses of (1) SDQ binary outcomes, which was not adjusted for maternal education, and (2) child “moderate/severe” sleep problem, which was not adjusted for child gender, maternal depression, or education, because there were potentially too few subjects with clinically high SDQ scores or a sleep problem to obtain stable estimates from models with all potential confounders included as predictors. The omitted variables were not strongly related to the respective binary outcomes.

All retained participants were analyzed in the groups to which they were randomized, applying the intention-to-treat principle. Confidence intervals from analyses of quantitative outcomes were validated by using the bootstrap method. 24 Intracluster (intra–maternal and child health unit) correlation coefficients from adjusted analyses are reported according to the CONSORT recommendations for cluster-randomized trials. 25 , 26 All data files were analyzed by using Intercooled Stata, version 11.1 for Windows (Stata Corp, College Station, TX).

Both the original trial (23067B) and 6-year-old follow-up (28137F) were approved by the Human Research Ethics Committee of The Royal Children’s Hospital, Melbourne.

At age 6 years, 225 of 326 children (69%) participated (see Fig 2 , participant flow). Of these, 193 (86%) participated in the home visit and 177 (79%) agreed to collect cortisol. Of the latter, 167 (94%) provided at least 1 cortisol sample and 149 (84%) provided the 2 cortisol samples and the collection time data required to categorize the diurnal profile as “abnormal” versus “normal.” We were unable to contact 49 of 326 families (15%), and 52 of 326 (16%) families declined for reasons including “too busy” ( n = 26), “not interested” ( n = 6), “personal reasons” ( n = 6), “child illness” ( n = 1), or no reason ( n = 13).

Table 2 shows the sample characteristics. In the control arm, children of mothers who completed a university degree were overrepresented, and children from disadvantaged backgrounds were underrepresented among those retained versus lost to follow-up; children of families who spoke a language other than English at home were underrepresented in both arms. Follow-up occurred at a mean age of 6.0 years (SD 1.9 months). Of the retained families, those who did and did not collect at least 1 cortisol sample had similar baseline characteristics (data available from authors on request), with the exception that those who did were less likely to speak a language other than English at home (13% vs 26%).

Baseline Characteristics According to Follow-up Status (ie, Retained or Lost to Kids Sleep Study) at Age 6 Years

All values are percentages, except where otherwise stated. EPDS, Edinburgh Postnatal Depression Scale, where EPDS >9 is the community cut point for depression; SEIFA, Socioeconomic Indexes for Areas, 2002 Australian census data for socioeconomic status by postal code.

There was little evidence of unadjusted or adjusted differences between trial arms on the child, child-parent, and maternal outcomes ( Table 3 ). Mean scores were almost identical between groups for the parent-reported child emotional, conduct behavior, and total mental health difficulties; Child Sleep Habits Questionnaire; psychosocial health-related quality of life; the child-parent relationship measures; and maternal mental health. The proportions of children with mental health problems, “moderate/severe” sleep problems, and authoritative parenting were also similar between trial arms. Consistent with these findings, the mean scores for children’s self-reported health-related quality of life and the proportions of children classified with chronic stress according to the objective physiologic cortisol measure were similar between intervention and control groups, providing little evidence that the early intervention harmed or benefited the intervention group with respect to child, child-parent, or maternal outcomes at 6 years.

Results of Regression Analyses Comparing the 2 Trial Arms on Child, Child-Parent, and Maternal Outcomes at Age 6 Years

CI, confidence interval; CPRS, Child-Parent Relationship Scale; CSHQ, Child Sleep Habits Questionnaire; DASS, Depression, Anxiety, Stress, Scale; ICC, intracluster correlation coefficient; PedsQL, Pediatric Quality of Life Inventory.

Summary statistics are quantitative (mean [SD]) except where specified as dichotomous (%).

The comparative statistic is the mean difference for quantitative outcomes (intervention minus control) and odds ratio for dichotomous outcomes (the risk of receiving the intervention compared with receiving usual care).

Negative ICCs for SDQ Total and Emotional clinical scores, and permissive parenting were truncated at zero.

Reference group for parenting styles is authoritative parenting. Authoritarian, permissive, and disengaged parenting styles (all negative outcomes) were similar between groups, and were therefore collapsed into a single category for analysis.

There was no evidence that a population-based targeted intervention that effectively reduced parent-reported sleep problems and maternal depression during infancy had long-lasting harmful or beneficial effects on child, child-parent, or maternal outcomes by 6 years of age. Thus, this trial indicates that behavioral techniques are safe to use in the long-term to at least 5 years postintervention.

The study had several strengths. This 5-year follow-up of a rigorously conducted randomized trial (the gold standard for assessing causality) 18 may represent the only opportunity to provide objective evidence investigating any lasting harms or benefits of behavioral infant sleep interventions. This is because, with their known short- and medium-term effectiveness, it is unlikely that new trials with true nonintervention controls and 5-year follow-up could now be ethically conducted. Where possible, we used well-validated, reliable outcome measures 15 , 27 , – 31 collected from multiple sources, including parent report, child report, and objective physiologic biomarkers. Although details of the 30% (290/982) of families originally excluded from the population sample were unknown, the enrolled participants covered a broad socioeconomic range and were similar to Australian and US normative data for maternal well-being and child temperament characteristics, 32 meaning that our findings should generalize to English-speaking families.

The study also had some limitations. Because 31% (101/326) of the original sample was lost to follow-up at age 6 years, the lower and upper bounds of the 95% confidence intervals did not rule out smaller long-term harms or benefits of the intervention that could be meaningful in public health research. 7 Nonetheless, the precision of the confidence intervals make clinically meaningful group differences unlikely. Loss to follow-up can also introduce internal bias and reduce generalizability. Regarding bias, the retained intervention and control participants were fairly balanced ( Table 2 ); however, as more non–English-speaking and disadvantaged families were lost to follow-up, our findings may be less generalizable to these participant groups. Finally, no validation studies of the categorical cortisol variable were available, but our own exploratory analyses within the combined cohort showing that abnormal cortisol was associated with poorer child and maternal well-being suggests that it was indeed functioning as a stress biomarker (A.P., M.W., H.H., unpublished data).

Our findings were entirely consistent with the longest follow-up study before the Kids Sleep Study, 6 , 20 which reported no differences between intervention and control arms on child internalizing and externalizing problems, sleep, or maternal mental health at child age 3 to 4 years (3 years postintervention). Thus, these new data, when interpreted with shorter follow-up data from >50 intervention studies (including 9 randomized controlled trials), suggest that behavioral sleep interventions have short- to medium-term benefits that fade beyond 2 to 3 years’ postintervention.

In the context of potential harm, it is unknown whether there are subgroups of infants (eg, those who have previously been maltreated, experienced early trauma, or are anxious children) for whom the techniques are unsuitable in the short- or long-term. 12 If supported by empirical investigation, there could be a case for using more gradual interventions such as adult fading instead of the more intensive graduated extinction (controlled comforting) to manage infant sleep. Along with trials like ours demonstrating that sleep problems can be effectively treated in older infants, recent efficacy trials for children younger than 6 months suggest that parent education programs that teach parents about normal infant sleep and the use of positive bedtime routines could effectively prevent later sleep problems. 4 , 8  

Our findings highlight the importance of access for parents to effective sleep management strategies and training for the health professionals in such strategies. Currently, the information available to parents about the effects of behavioral sleep strategies is inconsistent and out of date. For example, peak bodies including the Australian Infant Mental Health Association and the Australian Breastfeeding Association, which work to influence policy and practice but argue against the use of behavioral techniques like controlled comforting, have not updated position statements since the mid-2000s. Thus, there is a pressing need to deliver evidence-based information to parents and health care providers, which could be achieved, in part, by updating position statements, policy documents, and training curricula to reflect our current findings that behavioral sleep techniques are both effective in the short- and medium-term and safe to use in the long-term.

The intervention achieved all of its original aims (better infant sleep and lower maternal depression and health care costs in the short- to medium-term). The 6-year-old findings indicate that there were no marked long-term (at least to 5 years’ postintervention) harms or benefits. We therefore conclude that parents can feel confident using, and health professionals can feel confident offering, behavioral techniques such as controlled comforting and camping out for managing infant sleep.

adjusted odds ratio

Strengths and Difficulties Questionnaire

Drs Wake and Hiscock conceived the original study; Dr Price led the 6-year-old data collection phase; Drs Price, Wake, Ukoumunne, and Hiscock wrote the manuscript; all authors had full access to all of the data (including statistical reports and tables) in the study and take responsibility for the integrity of the data and the accuracy of the data analysis; Dr Price is the guarantor.

This trial has been registered with the ISRCTN Register ( http://isrctn.org ) (identifier ISRCTN48752250).

FUNDING: The Infant Sleep Study was funded by the Australian National Health & Medical Research Council (NHMRC) Project grant 237120 and the Pratt Foundation, and the follow-up Kids Sleep Study by the Foundation for Children (Project grant 180 2009) and the Victorian Government’s Operational Infrastructure Support Program. The authors’ work was independent of the funders (the funding source had no involvement). Dr Price was supported by a Melbourne Research Scholarship (The University of Melbourne) and the Murdoch Childrens Research Institute (MCRI), Dr Wake was supported by NHMRC Population Health Career Development Awards 284556 and 546405, and Dr Hiscock’s postdoctoral position was supported by NHMRC Population Health Capacity Building grant 436914 and Career Development Award 607351. The MCRI administered the grants and provided infrastructural support to its staff but played no role in the conduct or analysis of the trial.

We thank all the parents and children who took part in the Infant and Kids Sleep Studies; the Maternal and Child Health nurses from the cities of Bayside, Darebin, Hobson’s Bay, Manningham, Monash, and the Shire of Yarra Ranges who helped recruit and deliver the intervention in the Infant Sleep Study; and Lisa Quinn and Emily Roberts for their help with recruitment and data collection.

Competing Interests

Unethical and unscientific conclusions ignore how infants are harmed.

This article shows a lack of ethical monitoring by reviewers and editors. The authors state: "Behavioral sleep techniques have no marked long-lasting effects (positive or negative)." This is an unconscionable and unscientific conclusion since there is no way that the authors studied all possible effects nor did they examine exactly what the control group was doing (so, what are they comparing against?). They apparently ignored the vast amount of mammalian research showing that distressing young offspring leads to long term negative effects on mental and physical health. By allowing these unconscionable conclusions, you are encouraging irresponsible parenting behavior that will do great harm to children.

Conflict of Interest:

None declared

Sleep Training Not Harmful? Methodological Concerns Question Conclusion

The conclusion drawn by Price and colleagues that behavioral sleep techniques did not cause lasting harms (Five-Year Follow-Up of Harms and Benefits of a Behavioral Infant Sleep Intervention: Randomized Trial) can be challenged on several levels.

Treatment Integrity

Reliability of conclusions drawn in longitudinal research rests on treatment integrity of the initial design. In this Infant Sleep Study, initial treatment integrity was irreparably confounded when 40% of mothers in the treatment group did not engage in treatment (behavioral sleep intervention). This invalidates drawing statistically sound conclusions related to treatment effect initially and longitudinally. How can one draw conclusions about the efficacy or safety of an intervention when almost half of the treatment group declined treatment? Furthermore, the authors did not collect or report information on intensity or duration of treatment use or infant distress for those mothers engaged in the advised interventions.

Neither can the authors say for certain that control group mothers did not engage in a behavioral sleep intervention, since they did not collect that information either. Indeed, given the acceptance in the study location of use of behavioral sleep interventions, there is good reason to suspect that the control group might have been contaminated with subjects who used controlled crying.

Compromised Design

The research design is presented as a randomized controlled study. However, those directly involved in the intervention itself, i.e., nurses and the families, were aware of group membership. This introduces an expectancy effect (see Adair, 1984 for review) in which changes in participants' behavior following an intervention can be associated with the expectation of benefit rather than from the intervention itself.

Cortisol Protocol

The author's method of using diurnal cortisol patterns as an indicator of chronic stress caused by the behavioral intervention is highly questionable. The protocol for salivary collection as outlined -- 30 minutes post waking and noontime -- is not supported in the literature as a means of interpreting diurnal patterns of stress. There is no basis in scientific literature for expecting cortisol levels to be elevated five years after a stressor event, i.e., behavioral intervention, unless the child was subject to ongoing stress in the interim.

Need to Reconsider Conclusions

The authors have no valid basis for their assertion that behavioral sleep interventions cause no long-term harm. Thus, this article cannot and should not be presented as evidence of the long-term safety of behavioral sleep interventions that involve leaving infants to cry for varying periods of time. Given the author's own admission of no evidence of long- term benefit to the children in the intervention group - neither in terms of sleep quality nor measures of family mental health -- they and others who promote the use of behavioral sleep interventions should reconsider their assumptions that such treatments are necessary in order to prevent long-term sleep problems or other negative outcomes purported to be caused by untreated night waking. This is a particularly important reconsideration given the plethora of literature supporting synchrony, responsiveness, and breastfeeding--all of which are compromised in behavioral sleep interventions.

Re:Unethical and unscientific conclusions ignore how infants are harmed

Even as a lay person, I can see that this study proves nothing. The "control" group, if it even qualifies as control, could have actually gotten frustrated and just left their babies to cry to sleep (CIO)at some point. We don't know. If some or many of them did and if we hold the affects against the mammal studies Dr. Narvaez mentions, the test group who used "controlled crying" methods would actually be BETTER off in terms of unregulated stress (which is the concern of leading neuropsychological thought). So there is really no comparison happening here. In other words, you'd have a similar amount of harm in both groups, as Dr. Narvaez indicates. If these researchers are making the claim that everything that happened crying-wise must have been safe, because "all the kids seemed ok" at 6, that's not good science. I wish Allan Schore, one of the leading researchers of our time on the profound effects of early unregulated distress, would respond to this. One point I'm sure he would make, is that you can't necessarily see the effects of a brain wired for stress until later in life when adversity tests our core resilience.

Five Year Follow-up of Harms and Benefits of Behavioral Sleep Intervention: Randomized Trial

The recently reported paper Five Year Follow-up of Harms and Benefits of Behavioral Sleep Intervention: Randomized Trial.1 claims to show that the use of 'controlled comforting' more typically referred to as 'controlled crying' does not cause long-lasting harms or benefits to child, child-parent or maternal outcomes. We are concerned that these claims go beyond what this paper has reliably demonstrated. One of the main concerns about the use of such techniques is their impact on cortisol, and in this study the measure of 'abnormal' cortisol was only available for 46% of the sample, of whom 29% of the intervention group had abnormal cortisol levels compared with 22% in the control group. This difference would probably have been statistically significant had they been able to follow-up more infants. This study also did not utilise a good measure of infant attachment security using only a brief 5-item parent-report of 'disinhibited' attachment, which is typically only identified in children who have experienced abuse or severe neglect.2-3 The study also provides inadequate information about the extent to which these techniques were actually used. One of the main concerns about elevated cortisol levels during the first two years of life is the impact of 'toxic' levels of stress on a number of the developing neural systems, and the 'architecture of regions in the brain that are essential for learning and memory'.4 The current study made no attempt to measure the impact of such techniques on child development or learning. There has been no research to date that has examined the impact of the use of these 'extinction' techniques with infants less than 6 months of age, and the overall research at the current time strongly suggests that young infants should not be left to cry themselves to sleep5 This study does not show that there is no long-term impact of controlled comforting on infants, and more scientific research is needed about the potential benefits and harms before parents can be confidently reassured about the extent to which this technique should be used. In the meantime, there is extensive evidence available concerning the effectiveness of other techniques for promoting sleep and suggesting that parent education/prevention 'may set the standard as the most economical and time -efficient approach to behaviorally-based pediatric sleep problems'.6 1. Price AMH, Wake M, Ukoumunne OC, Hiscock H . Five-year follow-up of harms and benefits of behavioral infant sleep intervention: Randomized Trial. Pediatrics. 2012, 130(4), 643-651. 2. Zeanah CH. "Disturbances of attachment in young children adopted from institutions". Journal of Developmental and Behavioral Pediatrics. 2000, 21 (3): 230-36. 3. Zeanah CH, Scheeringa M, Boris NW, Heller SS, Smyke AT, Trapani J. "Reactive attachment disorder in maltreated toddlers". Child Abuse and Neglect. 2004, 28 (8): 877-88. 4. National Scientific Council on the Developing Child. Excessive Stress Disrupts the Architecture of the Developing Brain: Working Paper 2005, No. 3. p.3. 5. Middlemiss W, Granger DA, Goldberg WA, Nathans L (2012). Asynchrony of mother-infant hypothalamic-pituitary-adrenal axis activity following extinction of infant crying responses induced during the transition to sleep. Early Human Development . 2012, 88: 227-232. 6. Mindell JA, Kunh B, Lewin DS, meltzer LJ, Sadeh A (2006). Behavioral Treatment of bedtime problems and night wakings in infants and young children. Sleep. 29(10): 1263-1276.

Long-term effects of sleep training: A flawed methodology

The question of the long-term impacts of sleep training methods is one that is paramount given the preponderance of resources recommending such action. I was quite excited to read Price et al.'s article discussing research looking at this understudied issue. However, after reading the article I admit I'm rather confused as to how the authors can claim that they even addressed the question of interest given the major flaws in the research. Given the space constraints I will only address three of the largest methodological flaws.

Arguably the most serious problem is the lack of control in the control group. Despite randomizing the groups, little to nothing is known about either what the parents in the control group actually did vis-a-vis sleep behaviour or what the nurses discussed with the control group families. Apparently the researchers assumed that these families did not take part in any sleep training with no evidence to support such an assumption (especially when myriad resources suggest sleep training as a remedy for infant sleep problems). As is, the control group is not a true control group with respect to sleep training outcomes.

The second concern pertains to the misuse of the intention-to-treat principle. Although there was an element of self-selecting in the experimental group, that self-selection would not have unfairly biased the outcomes being measured. If indeed there are long-term effects, they have ostensibly been masked by the inclusion of the nearly 43% of the experimental group who refused the experimental protocol (i.e., sleep training). A parallel would be examinations of breastfeeding outcomes. Researchers do not examine these outcomes based on what women intended to do (despite that being important in many ways) but rather what the actual behaviour was. In these instances it is better to collect data on the possible confounds and control for them statistically than to utilize the intention-to-treat principle. Currently, we have outcomes for those who did not sleep train included in the outcomes of those who did which only serves to muddy the waters.

The third concern is that the measures used to assess child outcomes are parent-report. What the authors have presented is an assessment of parental perception of child attachment and behaviour; there is no objective or child-report measure included (with the exception of child health). Parents' perceptions may be colored by their choice (to take part in sleep training or not) and feelings of having intervened rather than the intervention itself and should be supplemented with other measures, especially as the researchers did do a home visit, making this type of assessment possible.

Overall it seems that the authors tried to make their data fit a pressing research question. Unfortunately, what has resulted is a study that has no bearing on the question of interest, and thus more research remains needed. Despite what the authors would like us to believe, we are no closer to knowing the long-term effects of sleep training than we were prior to the publication of this article.

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The Data All Guilt-Ridden Parents Need

What science tells us about breast-feeding, sleep training and the other agonizing decisions of parenthood.

Credit... Illustrations by Karolin Schnoor

Supported by

By Emily Oster

Dr. Oster is an economist.

• April 19, 2019

In 1980, 8.6 percent of first births were to women over 30 ; by 2015 this was 31 percent. This is more than an interesting demographic fact. It means that many of us are having children much later than our parents did. By the time a baby arrives, many of us have been through school, spent time in the working world, developed friendships, hobbies. And through all of these activities, we have probably grown used to the idea that if we work harder — at our jobs, at school, at banking that personal record in the half marathon — we can achieve more.

Babies, however, often do not respond to a diligent work ethic. Take, as an example, crying.

When my daughter, Penelope, was an infant, she was typically inconsolable between 5 and 8 p.m. I’d walk her up and down the hall, sometimes just crying (me crying, that is — obviously she was crying). I once did this in a hotel — up and down, up and down, Penelope screaming at the top of her lungs. I hope no one else was staying there. I tried everything — bouncing her more, bouncing her less, bouncing with swinging, bouncing with nursing (difficult). Nothing worked; she would eventually just exhaust herself.

I wondered whether this was normal. I’m an economist, someone who works with data. I wrote a book on using data to make better choices during pregnancy; it was natural for me to turn to the data again once the baby arrived.

[The topics new parents are talking about. Expert guidance. Personal stories that matter. Sign up to get NYT Parenting in your inbox every week .]

And here, faced with crying, I found that the data was helpful. We often say babies are “colicky,” but researchers have an actual definition of colic (three hours of crying, more than three days a week, for more than three weeks) and some estimates of what share of babies fit this description ( about 2 percent ). But the same data can also tell us that many babies cry just a bit less than that, and almost 20 percent of parents report their baby “cries a lot.” So I was not alone. The data also told me the crying would get better, which it eventually did.

But I also found, more so than in pregnancy, that there are limits to the utility of general information. Parenting is full of decisions, nearly all of which can be agonized over. You can and should learn about the risks and benefits of your parenting choices, but in the end you have to also think about your family preferences — about what works for you.

Breast-Feeding

Take breast-feeding . When I was pregnant and I imagined myself breast-feeding, I usually pictured myself out to brunch with some friends. When the baby was hungry I’d pop on my color-coordinated nursing cover, and she’d latch right on while I enjoyed my mascarpone French toast.

This is not what it was like at all . Like many women, I found breast-feeding incredibly hard. I have one particularly vivid memory of trying to nurse my screaming daughter in a 100-degree closet at my brother’s wedding.

These struggles are made worse by the societal, familial and medical testimonies to the many benefits of breast-feeding. Here, for example, is a partial list of supposed benefits to breast-feeding, culled from medical sources and less official parenting resources: smarter babies with less diarrhea and asthma, fewer ear infections, and a lower risk of obesity and diabetes, and thinner, happier moms with better friendships.

Better friendships? Don’t get me wrong — motherhood can be lonely and isolating, and meeting other moms is a great idea. That’s what stroller yoga is for. But I’m hard-pressed to figure out which of my friendships were enhanced by my attempts to feed a screaming baby in a closet.

Many of the benefits cited here do, however, have some basis in evidence, just not always especially good evidence. And even when the evidence is good, the benefits are smaller than many people realize. This is where being an economist comes in handy.

Most studies of breast-feeding are biased by the fact that women who breast-feed are typically different from those who do not. In the United States, and most developed countries, more educated and richer women are more likely to nurse their babies. This is the result of a host of factors, chief among them a lack of universal maternal supports.

Having more education and resources is, of course, linked to better outcomes for infants and children independent of breast-feeding. This makes it very difficult to establish the causal effect of breast-feeding — whether, for an individual woman, nursing her baby will make the child better off.

Some of the best evidence on breast-feeding comes from the Promotion of Breast-Feeding Intervention, or Probit , study , a large randomized trial from the 1990s run in Belarus, in which some of the mothers received breast-feeding guidance and support and some didn’t. Based on this data, the most well-supported benefits of breast-feeding are lower risks of gastrointestinal infections (with symptoms like diarrhea or vomiting) and of rashes and eczema early in life. To put some numbers to it, the study found that of the babies of a group of mothers encouraged to breast-feed , 9 percent had at least one episode of diarrhea, compared with 13 percent of the children of mothers who weren’t encouraged to breast-feed. The rate for rashes and eczema was 3 percent versus 6 percent.

Yet the study found no effect on respiratory infections, including ear infections, croup and wheezing. So why do we continue to see the “evidence-based” claim that breast-feeding reduces colds and ear infections? The main reason is there are many observational studies that do show that breast-feeding affects these illnesses.

For example, an observational study of nearly 70,000 Danish mothers and their children published in 2016 found that breast-feeding more than six months reduced the risk of an ear infection from 7 percent to 5 percent. This study was very careful, with excellent data that allowed the authors to adjust for a lot of differences across mothers and children.

But observational studies are less convincing than randomized trials because they have a harder time establishing causality. Should we give any weight to this evidence if we have the Probit trial?

On one hand, randomized evidence is clearly better. On the other hand, the Probit trial is only one study. If there are small benefits from breast-feeding, they might not show up as significant effects in a randomized trial, but we would still like to know about them. Given the weight of the evidence, I’d put the link between breast-feeding and a small reduction in ear infections in the “plausible” category. But there is nothing as compelling on colds and coughs.

What about long-term benefits, and the claims that breast-fed kids will grow up to be thinner, healthier and smarter? One woman told me her doctor had warned her that by quitting breast-feeding, she was costing her child three I.Q. points.

Let’s return from the land of magical breast milk to reality. Even in the most optimistic view about breast-feeding, the impact on I.Q. is small. Breast-feeding isn’t going to increase your child’s I.Q. by 20 points. How do we know? Because if it did, it would be really obvious in the data and in everyday life.

The question, really, is whether breast-feeding gives children some small leg up in intelligence. If you believe studies that just compare kids who are breast-fed to those who are not, you’ll find that it does. There is a clear correlation here — breast-fed kids do seem to have higher I.Q.s.

But again, this isn’t the same as saying that breast-feeding causes the higher I.Q. One study of Scandinavian 5-year-olds found that children who nursed longer had cognitive scores that were nearly 8 points higher on average. But their mothers were also richer, had more education and had higher I.Q. scores. Once the authors adjusted for even a few of these variables, the effects were much smaller.

In fact, the most compelling studies on this compare siblings, one of whom was breast-fed and the other not; these find no significant differences in I.Q. This same type of sibling study has also looked at obesity and, again, found little to no impact.

The good news for guilt-ridden moms is that there is little convincing evidence for any long-term effects like these. The Probit researchers followed the children in the trial through the age of 6½. They found no change in allergies or asthma , cavities , height, blood pressure, weight, or indicators for being overweight or obese .

If you’re a mother trying to decide whether breast-feeding is worth it or not, there’s one more piece of data you should take into account: the possible effects on your own health.

A lot of the claimed benefits of breast-feeding are about mothers, and many are bogus. Breast-feeding doesn’t seem to promote much additional weight loss or provide free birth control. There is no evidence linking breast-feeding and friendship quality.

However, there is real evidence for a link between breast-feeding and cancers, in particular breast cancer. A cross a wide variety of studies , there seems to be a sizable effect — perhaps a 20 percent to 30 percent reduction in the risk of breast cancer for women who breast-feed for longer than 12 months . In addition, the case for causality is bolstered by a concrete set of mechanisms. Researchers suggest that breast-feeding changes some aspects of the cells of the breast, which make them less susceptible to carcinogens.

After all that focus on the benefits of breast-feeding for kids, it may be that the most important long-term impact is actually on the health of the mother. Moms often feel selfish for thinking about their own wants and needs when faced with decisions about their kids. In this case, the data gives you permission to put yourself first for once.

Sleep Training

There are other fraught parenting decisions for which the evidence is much easier to understand than it is for breast-feeding. One example is sleep training.

Sleep training — colloquially, the “cry it out” technique — refers to any system where you leave the baby in his crib on his own at the start of the night, and sometimes let him fall back to sleep on his own if he wakes during the night. The name refers to the fact that if you do this, your baby will cry some. Pediatricians often recommend sleep training, and many parents do it.

But go on the internet, and you’ll find many articles detailing the extensive long-term damage sleep training will do to your child. At its core, the concern from the opponents of “cry it out” is that your baby will feel abandoned and, as a result, struggle to form attachments to you, and ultimately to anyone else.

This idea comes, perhaps surprisingly, from 1980s Romania, where thousands of children lived in orphanages with very little human contact for months or even years. One of the things visitors noticed in these places was the eerie quiet. Babies didn’t cry, because they knew no one would come. The argument is that “cry it out” does the same thing.

This is absurd. Sleep training methods do not leave the infant for months without any human contact, nor do they suggest subjecting children to the other types of physical and emotional abuse that occurred in those orphanages.

To learn about the impact of sleep training, we need to study it in the way it is actually used. Fortunately, many people have, and in a lot of those cases they used randomized trials.

Consider an Australian study of 328 mothers whose 7-month-old babies were having problems sleeping. Approximately half were assigned to do a sleep-training regime n, and the others were not. In the short term, the authors found significant benefits: The intervention improved sleep for children and also lowered parental depression. But they didn’t stop there.

They returned to evaluate the children a year later and five years later, when the children were 6. In this later follow-up , which included a subset of the original families, the researchers found no difference in any outcomes, including emotional stability and conduct behavior, stress, parent-child closeness, conflict or parent-child attachment. Basically, the kids who were sleep-trained looked exactly like those who were not.

These results are not an outlier. Review studies of sleep-training interventions do not find negative effects on infants . And many show sizable improvements in maternal depression and family functioning. Sleep affects mood, and parents who sleep less feel worse. The evidence paints a pretty pro-“cry it out” picture.

Nonetheless there are academic articles that argue against it. One small study that gets a lot of play shows that in the few days after sleep training, mothers are less stressed, but the same is not true of infants. The researchers interpret this as a signal that the mothers and children are losing emotional touch with each other, but this is a stretch. Why not interpret the evidence to say that cry-it-out relaxes parents without hurting children?

Fundamentally, the argument against sleep training is theoretical : that some children are devastated, even if those results don’t show up in the data, or that the damage may not manifest until babies are adults.

I think it is fair to say that it would be good to have more data. It’s always good to have more data! However, the idea that this uncertainty should lead us to avoid sleep training is flawed. Among other things, you could easily argue the opposite: Maybe sleep training is very good for some kids — they really need the uninterrupted sleep — and there is a risk of damaging your child by not sleep training.

Does this mean you should definitely sleep train? Of course not — every family is different, and you may not want to let your baby cry. But if you do want to sleep train, you should not feel shame or discomfort about that decision.

‘Working Moms’

Finally, there are some parenting decisions where the data just isn’t much help at all, and family preferences have to take the front seat. One example is the question of whether to work outside the home.

This decision is stressful. It often seems to define your whole parenting persona: What kind of mom are you? Are you a “stay-at-home mom” or, as the child of one of my friends once described her, a “stay-at-work mom”? Language like this is never helpful, and even less so when it frames this decision in such a gendered and heteronormative way. What if Dad stays home? What if there are two moms? Or only one parent?

Really, this decision could be better stated as: “What is the optimal configuration of adult work hours for your household?” Less catchy, but more helpful.

If you try to look to the evidence on what is “best” for children, you’ll be disappointed. There are studies of this, of course, but they’re hard to learn anything from, because it is extremely difficult to separate a family’s circumstances from decisions about employment. A 2008 meta-analysis found that children in families where one parent worked part-time and the other full-time performed best in school — better than children with two parents working full-time and better than those with one parent who didn’t work at all.

But again this is probably a result of many differences between those families, not just the mothers’ career decisions. There is really no compelling evidence that proves that having a stay-at-home parent affects child outcomes, positively or negatively.

(There is reliable evidence that time at home in a baby’s first few months is beneficial, but that is an argument for longer maternity leave, not for not working at all.)

This means that the decision really comes down to what works for your family. One part of this is obviously your budget, but the other part is your preferences.

I work because I like to. I love my kids! They are amazing. But I wouldn’t be happy staying home with them. It isn’t that I like my job better — if I had to pick, the kids would win every time. But the “marginal value” of time with them declines fast. (“Marginal value” will be familiar to anyone who remembers their Econ 101. There may not be any useful data on this question, but economic theory still comes in handy.) The first hour with my kids is great, but by the fourth, I’m ready for some time with my research. My job doesn’t have this nose-dive in marginal value — the highs are not as high, but the hour-to-hour satisfaction declines much more slowly.

It should be O.K. to say this. Just like it should be O.K. to say that you stay home with your kids because that is what you want to do. In our attempts to focus so much on what is best for our kids, it is a good idea to step back and think about what works for you.

And Everything Else

These decisions — breast-feeding, sleep training, working — are just three of many that will come up in the first year of a child’s life. More await, from co-sleeping to screen time and more.

One day, your child will have a temper tantrum. How on earth do you deal with that? Exorcism? And what about potty training? You may find your child is one of a surprisingly large share ( about 1 in 5 ) who refuse to poop in the toilet (it has a name: “stool toileting refusal”). In your pre-child life, you probably never thought about the question of how to encourage someone to poop in a particular location. But there you are, needing to find your way.

That lady on the internet comment board wants to tell you what to do, but she doesn’t live in your house, and she cannot know what is right for your family.

I’m not trying to give advice. I’m just arguing that in many cases the data can be helpful. But if the data falls short and you still want advice, let me pass along something our pediatrician once told me. It was our 2-year-old’s checkup, and I had my usual list of neuroses.

“We are going on this vacation, and there are bees,” I said. “It’s kind of isolated. What if Penelope is stung? She’s never been stung before. What if she’s allergic? How will I get her to a doctor in time? Should I bring something to be prepared for this? Should we test her in advance? Do I need an EpiPen?”

In other words, I had built up this elaborate and incredibly unlikely scenario in my head. I needed someone to remind me that yes, this could happen. But so could a million other things. Parenting is not actually about planning for every possible disaster.

The doctor paused. And then she said, very calmly:

“Hmm. I’d probably just try not to think about that.”

Emily Oster , an economics professor at Brown, is the author of “Expecting Better” and the forthcoming “Cribsheet: A Data-Driven Guide to Better, More Relaxed Parenting, From Birth to Preschool,” from which this essay is adapted.

The Times is committed to publishing a diversity of letters to the editor. We’d like to hear what you think about this or any of our articles. Here are some tips . And here’s our email: [email protected] .

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Fifteen years of research suggests that sleep training for babies can cause them more distress

True responsive care means adjusting to what babies need.

For parents all around the world, the scope of child-rearing practices, tips and guidance have long been a source of much conflict – especially when it comes to raising babies.

As trends rise and fall, one of the most divisive issues still seems to be whether or not “sleep training” – leaving babies alone to cry themselves to sleep – is as helpful as it’s often presented to be by advocates of the practice.

It used to be an accepted fact that babies tend to be easily distressed and struggle to sleep through the night. But these days many parents take a different approach, with little, if any intervention if their child wakes up crying.

Sleep training is often encouraged by authors, bloggers and some doctors, who claim it helps a baby to learn to calm themselves. But as researchers of the biological and psychological needs of infants for the past 15 years, we can confidently say this is an illusion as sleep training actually violates what early childhood experts call the need for safe, stable, and nurturing relationships.

It also violates the instincts of parents to comfort their young one. Indeed, from an evolutionary perspective , sleep training goes against our mammalian heritage – which emphasises companionship care from multiple responsive caregivers who provide extensive affection and constant comforting presence.

As social mammals, babies need affectionate touch and soothing care as they learn self-regulation and how to live outside the womb. If caregivers are not cuddling and physically present with their young for at least several hours a day, multiple systems can go awry because stress responses can be set to be overreactive, meaning that the brain will always be on the lookout for threats, even when such threats aren’t really there (e.g. when someone accidentally bumps into you but you take it as intentional provocation).

A big part of the problem with trying to sleep train a baby is that it undermines key aspects of the child’s development: brain function, social and emotional intelligence, trust in self, others and the world. Experiments carried out with isolated baby monkeys, depriving them of maternal touch (they could still smell, hear and see other monkeys), for example, found that when untouched, the baby monkeys developed all sorts of brain and social abnormalities . Humans are social mammals too and need responsive and affectionate care , at the very least.

Postnatal care experts who act as ‘safety net’ are concerned about wellbeing of babies born in Covid pandemic

Human offspring are particularly immature at full-term birth — 40-42 weeks — with only 25 per cent of adult brain volume in place. This is because when humans evolved to walk on two legs, the female pelvis narrowed .

As a result, human infants look like fetuses of other animals until around 18 months, when the upper skull bones finally fuse. The brain of a human baby triples in size by age three and during the early months and years, the child’s brain and body establish the functioning of multiple systems, in response to the care received. And the stress response can become overactive if babies are not kept content most of the time – which can cause long-term physical and mental health problems.

Ongoing biobehavioral synchrony with parents (i.e. the requirement of physical presence, the coupling of heart rhythms and autonomic function, coordination of brain oscillations, and coordination of hormone release like oxytocin) is critical in a baby’s life, and it lays the foundations for the child’s future self-regulation and social-emotional intelligence.

Because of this “cry-it-out” sleep training can be damaging to a rapidly growing brain – and to a growing psyche. Researchers have documented how, with sleep training, infants’ fight and flight instincts activate in the face of extensive distress, such as being left without comforting physical touch. When the distress of separation and lack of response goes on too long, the infant may quiet down but it is to reserve limited energy. This withdrawal into numbness can manifest as an impairment in social trust that can be carried into adulthood . These patterns can continue in adulthood when things become too stressful, shutting down thinking and feeling in situations where the individual is triggered into panic or anger.

Children’s brains and bodies are deeply shaped by caregiving practices and such moulding lasts a lifetime – unless therapy or other intervention occurs. In other words, parents have great influence on their child’s personality and socio-emotional intelligence. And when parents are comforting and calming , this facilitates children’s healthy development.

True responsive care means adjusting to what babies need, helping them stay calm, attending to the gestures and facial expressions that indicate discomfort and moving in to gently restore equilibrium. Crying is a late signal of need, so ignoring it all together may mean you’ve waited too long.

Darcia Narvaez is Professor of Psychology Emerita at the University of Notre Dame and Cathriona Cantio is Assistant Professor in the Faculty of Health Sciences at the University of Southern Denmark

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What Science Tells Us About Co-Sleeping vs. Sleep-Training

Awake again with a baby in the middle of the night, watching heinous reruns of Keeping Up with the Kardashians (What else is on a 3 am?), you dream of the nights when you slept more than 2 consecutive hours in a row.

You’re exhausted.

You’re a tired mom .

After months of sleep deprivation and looking at endless baby sleep tips, you know it’s not realistic to continue on this path of epic exhaustion. And yet, you aren’t really sure how to help both you and your baby come to terms with this whole sleep thing.

You’re friends dole out advice like tootsie rolls falling from a piñata. One friend recommends co-sleeping as the magic cure. Another friend recommends sleep training as the fix to all your sleep woes.

But…How do you make the “right” choice?

How do you know what’s right for you and your baby?

What if there was an easier way?

What if we stopped listening to what everybody told us was the “right” thing to do?

What if we simply looked at what scientific research says about co-sleeping and sleep training and everything in between and then looked at our personal family situation to make the best decision?

Parenting is filled with fear mongering. We are all up to our eyeballs in opinions, but I think it’s time to look at the real facts and put this great sleep debate to bed once and for all.

Of course there’s a book.

Parenting based on actual facts and the bigger scientific picture (not just one study, but a multitude) is a win-win for me. The best part of the book is Callahan’s attempt to share factual information with readers without prescribing one specific method over another. After presenting all of her research, she reminds parents to take the knowledge learned, combine it with real life, and make common sense decisions.

Now that you know the source, let’s dive in and talk about Callahan’s baby sleep research and the conclusions she draws.

What does science say about bed sharing?

Many parents choose to bed-share due to a specific parenting philosophy or because the physical closeness of the baby makes night waking easier on parents. Most studies that Callahan examined show that bed-sharing babies and moms tend to wake up more often and may experience a shorter duration of nighttime sleep than babies and moms who sleep in separate beds.

The tricky part comes as the baby gets older and enters into the toddler years. One study cited by Callahan found that 2 year olds who breastfed and bed-shared slept for an average of 4.8 hours at a time, while those who breastfed but sleep alone averaged a stretch of 6.9 hours. And 2 year olds, who no longer breastfed and slept alone, averaged a 9.5 hour stretch at night.

So what is better for babies—consolidated sleep or frequent waking and feeding?

The answer is we don’t know yet. Looking at the current evidence, there is no difference among growth rates or attachment regardless of parental choice.

Bottom line:

Whether you choose solo sleeping or bed sharing, emotional availability seems to be the most important factor towards healthy development. This means being sensitive to your baby’s cues and responding appropriately.

What does science say about bed sharing safety?

If you do choose to bed share, there are several important recommendations based on science to safely protect your child.

• Bed sharing with your baby before the age of 3 or 4 months increases the risk of Sudden Infant Death Syndrome (SIDS). It is recommended to use a bassinet or safe co-sleeper next to the bed during the initial months of life.
• Always put your baby to sleep on his back.
• Sleeping in a couch or chair with your baby dramatically increases the risk of SIDS and suffocation. If you decide to co-sleep, sleeping with your baby in a bed is the safest option.
• Avoid bed sharing if either parent smokes or drinks alcohol or the baby is premature, as this increases the risk of SIDS as well.
• Ensure your mattress is firm and flat.
• Remove the mattress from the bed frame and place it on the floor and away from walls.
• Avoid side rails since the can entrap the baby.
• Minimize all pillows and blankets and keep them away from baby.
• If bed sharing with a baby, keep other children, non-parents, and pets free from the bed.
• Keep your baby warm using a safe sleep sack rather than loose blankets or a hat.

It’s important to note that outside of Western cultures, bed sharing is very common; however, their bed sharing environments are vastly different. Many countries, where bed sharing is commonplace, use a pallet or very firm futon on the floor to ensure safety.

What does science say about self-soothing?

Basically, a baby is considered a self-soother if he or she wakes during the night and is able to return to sleep independent of parental intervention. According to Callahan, “It’s as if they wake up, look around, and think, ‘Oh yes, here I am in my crib still. Nothing interesting going on here. Yawn. I guess I’ll go back to sleep.’” (p. 124).

Several studies show that when parents are given tools to help their babies gently self-soothe, babies will sleep longer and cry out for their parents less often during the night as early as a few months of age.

Best ways to help your baby learn to self-soothe:

• Laying the baby down awake, but drowsy for naps and bedtime.
• When your baby wakes during the night, wait a moment before responding, especially if the baby is making quiet noises.

What does science say about sleep-training?

Depending on who you ask, sleep training involves various methods, which may be abrupt or gradual. All sleep training involves letting your baby learn to self-soothe so he or she can fall asleep without parental help.

Studies show that sleep training leads to “reduced bedtime struggles, fewer night wakings, and longer sleep for both baby and parents, better maternal mental health, and even improved baby temperament and mood.” (p. 133).

Sleep training isn’t a perfect fit for every baby and family. Science teaches us that not every baby will respond well to sleep training. As a parent, it’s important to use common sense to determine if sleep training is working for your baby, knowing when to “throw in the towel” if things are going poorly.

It’s important to note that sleep training does not eliminate night waking altogether, but rather it reduces it over time. If your baby wakes during the night and experiences a legitimate need, parents should meet those needs.

What does science say about self-soothing and sleep-training safety?

There is no scientific evidence that responsible sleep training will hurt your child. Experts and parents against sleep training often cite studies that claim sleep-training will damage or hurt your child.

It’s important to note in Callahan’s research that all of those studies are about “babies who were subjected to chronic neglect or abuse or raised in orphanages, lacking strong attachment figures. Or they’re about nonhuman primates or rodents separated from their mothers for extended periods of time. These are examples of chronic, toxic stress. ” (p. 133).

Callahan further explains that there is no evidence demonstrating sleeping training as harmful when parents utilized responsible techniques, gentle boundaries and employed positive parenting interactions.

The big picture.

Baby sleep solutions are not a perfect science. Whatever sleep choices you make for your child and family, do it mindfully, lovingly and intentionally. Making responsible, common sense choices comes from listening to your gut, doing your research, understanding actual facts, and avoiding much of the negative fear mongering opinions in the parenting community.

Rest easy mama. A good night’s rest is just around the corner.

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About Lauren Tamm

I'm Lauren, a military spouse and Language of Listening® master parent coach. I write about my crazy parenting adventures, discovering happiness in motherhood and navigating the ups and downs of military life. I spend my days re-heating coffee while chasing my kids around the house. Hang around for a bit and join the fun!

Reader Interactions

Great post! I love well-researched articles like this, so thank you for taking the time to write it. I particularly like the part about the “Experts and parents against sleep training often cite studies that claim sleep-training will damage or hurt your child.” Exactly. I know some people who are SO against sleep training or letting a baby cry at all because of these studies and they often make anyone who does otherwise feel like crap.

Sleep training for the win in my family!

I’m so glad you liked it! I tried to stay as unbiased as possible. I truly believe each family needs to find what works for them. There isn’t a right or wrong answer, so long as we make an informed decision.

There are plenty of studies about sleep deprivation for adults. If your child sleeps longer, you get to, too!

I think that co-sleeping is wonderful!? But we can’t sleep with our kids forever. I shared my bed with my baby girl for the first 9 months – as long as I was breastfeeding. When she turned 9 months she didn’t want to eat my milk anymore and I decided that it’s the best time to teach her to fall asleep on her own in her crib. I used the HWL method by Susan Urban from her guide “How to teach a baby to fall asleep alone”. It worked BRILLIANTLY on my daughter. Can recommend it to anybody who wants to sleep train.

I’ve never responded to one of these before but I’m so impressed with How to teach a baby to fall asleep alone guide that I wanted to share it with you. I shared my bed with my LO for more than a year and I decided to change it. I’ve followed the instructions from Urban’s guide and after 2 days my son was able to fall asleep and sleep all night long in his crib. It happened so fast and easy that I’m still a bit shocked 🙂 Big thanks for sharing.

It’s fantastic – I wasn’t sure about following books or guide or things like this but Urban’s guide made me happy 🙂 I still can’t really believe that it took us only 3 days to stop rocking our son to sleep! pretty amazing!!!

love this book. after 11 months of not getting much sleep it finally made me to convince my self to try this technique and it worked during 4 days

Preach! What a well written and thoroughly researched piece! I’m always warry when clicking on an article that talked about sleep training, since the AP movement is in full-swing and there is so much woo out there

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No Need for Guilt, Sleep Training Doesn't Ruin Your Baby Bond

Anna Bizon / Getty Images

Key Takeaways

• A new study shows babies who are sleep trained slept better and longer than babies who were not sleep-trained.
• Sleep training did not affect the bonding between parents and infants.
• The decision to sleep train is up to each individual family, but this study can help parents ease parents anxious minds about sleep training.

If you're a parent, chances are you've been there—we all have. You have a baby that won’t sleep when expected, who then cries incessantly because they are overtired. The exhausted parent in turn also gets cranky and the cycle seems to be continuous and torturous. Sleep training may seem like the obvious answer but some parents worry the process will break the parent-child bond , and possibly damage the child’s mental health.

New research should help calm some of those fears. It not only showed that sleep training worked, but it didn't impact the parents' bond with their babies. This study was conducted in collaboration with Nanit Lab, the research arm of Nanit—a company that makes high-tech baby monitors . The monitors use technology to help track the baby's sleep and growth.

In the study published in the Journal of Pediatrics , 2,090 Nanit users were surveyed about their experience with infant behavioral sleep interventions (BSIs). This is also known as sleep training. Participants were all parents of U.S. infants between the ages of 3 and 18 months. Approximately 64% of parents reported using BSIs.

Sleep Training Doesn't Break Your Bond With Baby

Sleep training is a safe, effective way to help your baby get the sleep they need to set them up for a lifetime of sleep health. ”Babies who were sleep trained slept better and longer than babies who were not," says Natalie Barnett, PhD and vice president of clinical research at Nanit .

Not only are sleep-trained babies sleeping better, but researchers found no correlation between sleep training and negative outcomes such as depression, sleepiness, or damage to parent-infant bonding. This is great news for parents concerned about the connection and safety of sleep training methods. 

“There was no evidence of sleep training interfering with the parent-child bond," Dr. Barnett explains. "There was no difference in attachment between the babies who were sleep trained and the babies who were not,”

Jessica Madden, MD , a board-certified pediatrician, neonatologist, and International Board-Certified Lactation Consultant (IBCLC) agrees. She says she doesn't believe sleep training interferes with the bonding of parents with older infants or children.

Dr. Madden however has one caveat.  She doesn’t recommend sleep training before 4-5 months of age . Babies should get comfortable falling asleep on their own at this age before the separation anxiety phase which usually starts around 8 months old. "It's really important to not initiate sleep training for any babies who have current problems with growth, weight gain, and nutrition or other chronic health problems," she adds.

Babies Who Are Sleep Trained Get More Zzz’s

Sleep training teaches children how to fall asleep faster, stay asleep longer, and the ability to get themselves back to sleep when they wake. These are vital healthy habits that help children feel their best.

“We often don’t realize how impactful sleep training can be for parents as well," says Sydney Lucas , a certified sleep training consultant with Wee-Sleep. "Having guidance and support helps ease parents' stress, anxiety, and exhaustion that comes with lack of sleep and frustration around what to do and how.”

Lucas says having a plan helps parents feel in control and can be life-changing for many families. Children who sleep better are emotionally adjusted , have less difficulty learning , less fussiness, and have a reduced risk of health problems as they grow. Restorative sleep is crucial for the development and overall well-being of the whole family.

From a developmental standpoint, infants do not sleep through the night, on average, until they are at least 6 months old. Dr. Madden advises parents to have realistic expectations and goals if they start to sleep train. “Sleeping through the night means having one stretch of sleep that is at least 6 hours long—so sleeping from 10 p.m. until 4 a.m. is considered to be sleeping through the night," advises Dr. Madden.

It's important to remember there's no 'one size fits all' approach to sleep training. The decision whether or not to start to sleep train, and when, needs to be made from a holistic standpoint. Dr. Madden says parents should factor in the baby’s temperament, sleep environment, method of feeding, age and size of baby, and also parents’ goals and desires. 

Types of Sleep Training Studied

• Unmodified extinction (“cry it out”): Parents leave their baby’s room at bedtime without soothing them when they cry until they can fall asleep on their own. 
• Modified extinction (“controlled crying”): Similar to “cry it out”, but gradual. Parents soothe their babies when they cry, but gradually increase the amount of time until they soothe.
• Parental presence: The parent stays in the room with the baby as they fall asleep, but gradually moves farther away until the baby can fall asleep without them.

Different Methods Yield Different Outcomes

In the Journal of Pediatrics study, babies who were left to cry it out (unmodified extinction) or experienced controlled crying (modified extinction) got the equivalent of an extra night of sleep per month compared to babies who were not sleep-trained.

Controlled crying was the most common approach. "Unmodified extinction was the method that was the fastest to see improvements and took the shortest time to complete, while parental presence took significantly longer to see improvements and to complete,” says Dr. Barnett.

Critics of the unmodified extinction method worry that letting their baby cry it out without comfort will elevate the baby's stress levels.

Dr. Barnett says the benefit of the parental presence method was it was the easiest method for parents to implement. It was significantly easier on the parents than modified or unmodified extinction. However, the study found that it took parents more than 50% longer to see improvements in infant sleep using parental presence compared to unmodified or modified extinction.

What if I Don’t Want To Sleep Train My Baby?

Ultimately, the decision to sleep train is up to the parents. The most common concern parents have is causing emotional stress and damage to the baby. Lucas shares a combination method she often recommends.

“Putting your baby to bed while he or she is still awake, and a parent stays nearby to support them when needed until their baby falls asleep. This is a gentle, supportive way to help your baby learn to sleep without leaving them to cry it out or do it all on their own,” she says.

Parents who did not implement sleep training visited their infants’ cribs 37 times per month more than parents who sleep train their babies. Additionally, parents who did not implement sleep training or relied on parental presence were more likely to perceive their infants' sleep as problematic.

“Sleep training, if done in a developmentally appropriate manner, can help older infants and toddlers start to sleep through the night,” adds Dr. Madden. “To my knowledge, there are not any scientific or research studies showing any real benefits of sleep training. The main benefit I can tell is for both parents and children to get longer stretches of sleep at night."

What This Means For You

Sleep training your baby is safe and can be beneficial for both the baby and the parents. Having guidance and support helps ease parents' stress, anxiety, and exhaustion from lack of sleep and frustration around what to do and how to do it. Speak with your child’s pediatrician before attempting sleep training. The use of a certified sleep training expert can also help to answer any questions and guide you.

Kahn M, Barnett N, Gradisar M. Implementation of behavioral interventions for infant sleep problems in real-world settings .  The Journal of Pediatrics . 2022:S0022347622010009. doi:10.1016/j.jpeds.2022.10.038

Mindell JA, Kuhn B, Lewin DS, Meltzer LJ, Sadeh A, American Academy of Sleep Medicine. Behavioral treatment of bedtime problems and night wakings in infants and young children . Sleep. 2006;29(10):1263-1276.

Mindell JA, Leichman ES, DuMond C, Sadeh A. Sleep and social-emotional development in infants and toddlers .  Journal of Clinical Child & Adolescent Psychology . 2017;46(2):236-246. doi:10.1080/15374416.2016.1188701

Magee CA, Gordon R, Caputi P. Distinct developmental trends in sleep duration during early childhood .  Pediatrics . 2014;133(6):e1561-e1567. doi:10.1542/peds.2013-3806

Pennestri MH, Laganière C, Bouvette-Turcot AA, et al. Uninterrupted infant sleep, development, and maternal mood. Pediatrics . 2018;142(6):e20174330. doi:10.1542/peds.2017-4330

Gradisar M, Jackson K, Spurrier NJ, et al. Behavioral interventions for infant sleep problems: a randomized controlled trial . Pediatrics. 2016;137(6):e20151486. doi:10.1542/peds.2015-1486

Mindell JA, Williamson AA. Benefits of a bedtime routine in young children: Sleep, development, and beyond . Sleep Med Rev . 2018;40:93-108. doi:10.1016/j.smrv.2017.10.007

By Taayoo Murray Taayoo is a New York City-based writer and boy mom who writes about family, health & wellness, and lifestyle. Her work has been published in national publications like Parents, Health, Huffpost Well, Verywell Health, Yahoo Life, Business Insider, New York Times Kids, Giddy, and others.

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Psychological and Physical Approaches for Sleep Disorders: What the Science Says

Clinical Guidelines, Scientific Literature, Info for Patients:  Psychological and Physical Approaches for Sleep Disorders

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Current clinical practice guidelines from the  American Academy of Sleep Medicine (2021) recommend psychological and behavioral interventions in the treatment of chronic insomnia disorder in adults. 

• The American Academy of Sleep Medicine guidelines state: “We recommend that clinicians use multicomponent cognitive behavioral therapy for insomnia (CBT-I) for the treatment of chronic insomnia disorder in adults (strong recommendation). We suggest that clinicians use relaxation therapy as a single-component therapy for the treatment of chronic insomnia disorder in adults (conditional recommendation).” The authors of the guidelines also noted that there were fewer than three studies meeting their inclusion criteria for the use of cognitive therapy, paradoxical intention, mindfulness, biofeedback, and intensive sleep retraining; as a result, no recommendations were made about these treatments.

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• Clinical practice guidelines  issued by the American Academy of Sleep Medicine in 2021 recommend psychological and behavioral interventions for the treatment of chronic insomnia disorder in adults. The guidelines state: “We recommend that clinicians use multicomponent cognitive behavioral therapy for insomnia (CBT-I) for the treatment of chronic insomnia disorder in adults (strong recommendation).”
• A 2018 analysis of pooled data from 4 randomized controlled trials of 546 peri- and postmenopausal women with insomnia and bothersome vasomotor symptoms found that CBT-I produced the greatest reduction in Insomnia Severity Index (ISI) from baseline compared to an education control. 
• A  2014 randomized controlled trial  examined the comparative efficacy of cognitive behavioral therapy, tai chi, and a sleep seminar education control in 123 older adults with chronic and primary insomnia. The study found that cognitive behavioral therapy performed better than tai chi and sleep seminar education in remission of clinical insomnia. The cognitive behavioral therapy group also showed greater improvement in sleep quality, sleep parameters, fatigue, and depressive symptoms than the tai chi and sleep seminar education groups.

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• CBT-I is considered safe.

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There is a small amount of low-quality evidence that relaxation techniques by themselves can help with chronic insomnia.  Relaxation techniques may be recommended in certain situations, depending on individual preferences, health provider qualifications, and treatment availability. 

Current clinical practice guidelines from the American Academy of Sleep Medicine (2021) conditionally recommend relaxation therapy as a single-component therapy for the treatment of chronic insomnia disorder in adults. 

• Clinical guidelines from the American Academy of Sleep Medicine (2021) made a conditional recommendation to use relaxation therapy as a single-component therapy based on “a small body of low-quality evidence from five studies showing clinically meaningful improvements in one critical outcome, consideration that some patients prefer relaxation therapy, the fact that mental health providers are trained to deliver this form of treatment, and the potential for relaxation therapy to require only limited resources.”
• A 2018 systematic review looked at 27 studies of psychological interventions to try to improve sleep. The studies involved 2,776 college students who ranged from healthy sleepers to those with a diagnosed sleep disorder. About 22 percent of the studies investigated “relaxation, mindfulness, hypnotherapy” treatments. This review recommended cognitive behavioral therapy to improve sleep in college students. The review also found that relaxation approaches helped somewhat with sleep quality and sleep problems but especially with mental health. The authors recommended that “relaxation, mindfulness, hypnotherapy” treatments be combined with cognitive behavioral therapy as a way to enhance mental health benefits.
• Relaxation therapies for insomnia are considered safe.

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Yoga has been shown to be helpful for sleep in several studies of cancer patients, women with sleep problems, and older adults and in individual studies of other population groups, including people with arthritis and women with menopause symptoms. However, a 2019 clinical practice guideline from the U.S. Department of Veterans Affairs and U.S. Department of Defense said there was insufficient evidence to recommend for or against yoga for treating insomnia.

• A  2020 systematic review and meta-analysis of 19 studies involving a total of 1,832 participants found positive effects of yoga in 16 randomized controlled trials, compared with the control group, in improving sleep quality among women using Pittsburgh Sleep Quality Index (PSQI); however, 2 studies revealed no effects of yoga compared to the control group in reducing insomnia among women using ISI. Seven studies revealed no evidence for effects of yoga compared with the control group in improving sleep quality for women with breast cancer using PSQI, while four studies revealed no evidence for the effects of yoga compared with the control group in improving the sleep quality for peri/postmenopausal women using PSQI.
• A  2020 secondary analysis of a randomized controlled trial involving 320 adults with chronic low-back pain and poor sleep quality prior to the intervention found modest but statistically significant improvements in sleep quality in the yoga (12 weekly yoga classes) and physical therapy groups.
• A  2019 systematic review of 11 studies that evaluated the use of yoga to manage stress and burnout in health care workers concluded that yoga is effective in improving physical problems and quality of sleep, as well as reducing stress levels and burnout. However, the authors of the review noted that it would be necessary to broaden the subject further and acquire more robust scientific evidence by designing and implementing research studies equipped with a solid methodological structure on bigger sample groups.
• A  2013 multicenter, randomized controlled trial evaluated the effect of yoga on sleep quality in 410 cancer survivors suffering from moderate or greater sleep disruption between 2 and 24 months after surgery, chemotherapy, and/or radiation therapy. The study found that compared with standard care, yoga participants demonstrated greater improvements in global sleep quality and subjective sleep quality, daytime dysfunction, wake after sleep onset, sleep efficiency, and medication use at postintervention.
• A  2022 randomized controlled trial  investigated the effects of yoga (duration of 20 weeks) on menopausal symptoms and sleep quality across menopause statuses in 208 women. Based on participant responses to questionnaires, the study found that yoga decreased menopausal symptoms, with the strongest effects noted in postmenopausal women, followed by perimenopausal women. In addition, yoga significantly improved sleep quality in postmenopausal and perimenopausal women after controlling for social support, depression, anxiety, stress, and menopausal symptoms; however, yoga did not affect sleep quality in premenopausal women.
• Yoga is generally considered a safe form of physical activity for healthy people when performed properly, under the guidance of a qualified instructor. However, as with other forms of physical activity, injuries can occur. 
• The most common injuries are sprains and strains, and the parts of the body most commonly injured are the knee or lower leg. Serious injuries are rare. The risk of injury associated with yoga is lower than that for higher impact physical activities.
• Hot yoga has special risks related to overheating and dehydration.
• Pregnant women, older adults, and people with health conditions should talk with their health care providers and the yoga instructor about their individual needs. They may need to avoid or modify some yoga poses and practices. 

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Results of several studies, using objective and subjective measures, have shown that tai chi may be helpful for people with sleep problems. However, a 2019 clinical practice guideline from the U.S. Department of Veterans Affairs and U.S. Department of Defense said there was insufficient evidence to recommend for or against using tai chi to treat insomnia.

• A 2020 systematic review and meta-analysis of 20 randomized controlled studies from 5 countries involving a total of 1,703 patients found that compared with nontherapeutic and other active treatments, tai chi has a positive effect on improving sleep quality. An in-depth analysis showed that 24-form and 8-form Yang-style tai chi had significant positive effects on sleep quality, as assessed by the Pittsburgh Sleep Quality Index (PSQI).
• A 2021 randomized controlled trial assigned 320 participants 60 years or older and with chronic insomnia to three groups: 12-week tai chi training, 12-week conventional exercise, and no intervention control. The study found that compared with the control group, the exercise and tai chi groups showed improved sleep efficiency, reductions of wake time after sleep onset, and reduced awakenings as measured by actigraphy. However, there were no significant differences between the exercise and tai chi groups.
• Tai chi appears to be safe. A 2019 meta-analysis of 24 studies (1,794 participants) found that the frequency of adverse events was similar for people doing tai chi, another active intervention, or no intervention. 

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A 2019 clinical practice guideline from the U.S. Department of Veterans Affairs and U.S. Department of Defense said there was not enough evidence to know whether mindfulness meditation is helpful for people with insomnia, and a 2021 clinical practice guideline from the American Academy of Sleep Medicine said there was not enough evidence to make recommendations on using mindfulness by itself for insomnia. 

• A 2022 review of 20 studies and 2,890 participants found that mindfulness-based stress reduction might be ineffective for improving sleep quality in people with insomnia, but the authors noted that the studies were small and showed bias.
• A   2019 systematic review and meta-analysis of 18 studies (1,654 total participants) found that mindfulness meditation practices improved sleep quality more than education-based treatments. However, the effects of mindfulness meditation approaches on sleep quality were no different than those of evidence-based treatments such as cognitive behavioral therapy and exercise.
• Results from a  2015 randomized controlled trial  involving 60 adults aged 75 years and over with chronic insomnia suggest that the mindfulness-based stress reduction program could be a useful treatment for chronic insomnia for this age group. 
• Meditation and mindfulness practices usually are considered to have few risks. 

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A 2022 review of 13 studies with 1,007 adult participants found that listening to music may lead to improved reports of sleep quality among people with insomnia. However, there was not enough good-quality evidence to determine the effect of listening to music on the severity of insomnia or the number of times a person wakes up. 

• A  2022 review of 13 studies with 1,007 adult participants found that listening to music may lead to improved reports of sleep quality among people with insomnia. However, there was not enough good-quality evidence to determine the effect of listening to music on the severity of insomnia or the number of times a person wakes up. The results showed that listening to music may slightly improve sleep-onset latency, sleep duration, sleep efficiency, and daytime effects.
• In general, research studies of music-based interventions do not show any negative effects. However, listening to music at too high a volume can contribute to noise-induced hearing loss. 
• Because music can be associated with strong memories or emotional reactions, some people may be distressed by exposure to specific pieces or types of music.

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A 2019 clinical practice guideline from the U.S. Department of Veterans Affairs and U.S. Department of Defense said there was not enough evidence to recommend for or against using acupuncture for insomnia, except for a weak recommendation for auricular acupuncture, which involves specific points on the outer ear. Results from some studies suggest that auricular acupuncture may help improve insomnia; however, many of the studies conducted on acupuncture for sleep disorders are small and are of low quality.

• A  2021 review of 11 studies and 775 participants suggested that acupuncture may help improve insomnia, but the studies were small, differed from each other in many ways (e.g., treatment dosage, acupoint selection), and judged to be low quality. 
• A  2019 clinical practice guideline from the U.S. Department of Veterans Affairs and U.S. Department of Defense said there was not enough evidence to recommend for or against using acupuncture for insomnia, except for a weak recommendation for auricular acupuncture, which involves specific points on the outer ear. 
• A  2020 evaluation of 7 systematic reviews (10,001 participants) on auricular acupuncture for insomnia found that the reviews suggested auricular acupuncture may be beneficial, but the quality of most of the reviews was low or critically low and the quality of the studies within the reviews was poor.
• Relatively few complications from using acupuncture have been reported.  However, complications have resulted from use of nonsterile needles and improper delivery of treatments.  When not delivered properly, acupuncture can cause serious adverse effects, including infections, punctured organs, and injury to the central nervous system. 

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A scoping review of sleep education and training for nurses

Affiliations.

• 1 Division of Science Integration, National Institute for Occupational Safety and Health, Centers, for Disease Control and Prevention, 1090 Tusculum Ave, Cincinnati, OH 45226, USA; University of Cincinnati, College of Nursing, 3110 Vine St, Cincinnati, OH 45219, USA. Electronic address: [email protected].
• 2 Division of Science Integration, National Institute for Occupational Safety and Health, Centers, for Disease Control and Prevention, 1090 Tusculum Ave, Cincinnati, OH 45226, USA; Oak Ridge Institute for Science and Education, P.O. Box 117, Oak Ridge, TN 37830, USA; Division of Environmental Health Science and Practice, National Center for Environmental, Health, Centers for Disease Control and Prevention. Mailstop S106-5, 4770 Buford Highway, Atlanta, GA 30341, USA. Electronic address: [email protected].
• 3 Division of Science Integration, National Institute for Occupational Safety and Health, Centers, for Disease Control and Prevention, 1090 Tusculum Ave, Cincinnati, OH 45226, USA. Electronic address: [email protected].
• 4 Division of Science Integration, National Institute for Occupational Safety and Health, Centers, for Disease Control and Prevention, 1090 Tusculum Ave, Cincinnati, OH 45226, USA. Electronic address: [email protected].
• PMID: 37080122
• PMCID: PMC10180237 (available on 2024-06-01 )
• DOI: 10.1016/j.ijnurstu.2023.104468

Background: Shift work and resulting sleep impairment among nurses can increase their risk for poor health outcomes, occupational injuries, and errors due to sleep deficiencies. While sleep education and training for nurses has been recommended as part of a larger fatigue risk management system, little is known about training programs designed specifically for nurses.

Objective: Investigate the literature for current sleep education or training programs specifically for shift working nurses, with intent to assess training content, delivery characteristics, and outcome measures.

Design: A scoping review conducted October 2020 through September 2021.

Methods: The bibliographic databases Cumulative Index of Nursing and Allied Health (CINAHL), Scopus, PubMed, and NIOSHTIC-2 were searched using words such as "nurse," "sleep hygiene," "shift work," and "education". Studies were included if they: 1) were original research; 2) discussed sleep education, training, or sleep hygiene interventions; 3) included a study population of nurses engaging in shift work; 4) focused on sleep as a primary study measure; 5) were written in English language; and 6) were published in 2000 or later.

Results: Search results included 17,237 articles. After duplicates were removed, 14,620 articles were screened. Nine articles were found to meet established criteria. All studies included sleep hygiene content in the training programs, with five studies adding psychological and/or behavior change motivation training to support change in nurse sleep habits. Three studies added specific training for nurses and for managers. Delivery modes included in-person training of various lengths and frequency, mobile phone application with daily engagement, an online self-guided presentation, and daily reading material coupled with audio training. Pittsburgh Sleep Quality Index and Epworth Sleepiness Scale were the outcome measures most frequently used. Although studies demonstrated improved sleep measures, most were pilot studies testing feasibility.

Conclusion: Although there is a paucity of studies focused on sleep education and training for shift working nurses, we found the inclusion of sleep hygiene content was the only common characteristic of all nine studies. The variability in training content, delivery methods, and outcome measures suggests further research is needed on what constitutes effective sleep education and training for nurses.

Keywords: Healthcare worker; Nurse; Shift work; Sleep education; Sleep hygiene; Sleep training.

Copyright © 2023 Elsevier Ltd. All rights reserved.

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• Perspective
• Published: 22 December 2023

Optimizing the methodology of human sleep and memory research

• Dezső Németh   ORCID: orcid.org/0000-0002-9629-5856 1 , 2 , 3   na1 ,
• Emilie Gerbier 4   na1 ,
• Jan Born 5 ,
• Timothy Rickard 6 ,
• Susanne Diekelmann 5 , 7 ,
• Stuart Fogel   ORCID: orcid.org/0000-0002-3227-5370 8 ,
• Lisa Genzel 9 ,
• Alexander Prehn-Kristensen 10 , 11 ,
• Jessica Payne 12 ,
• Martin Dresler   ORCID: orcid.org/0000-0001-7441-3818 13 ,
• Peter Simor 2 , 14 ,
• Stephanie Mazza 15 ,
• Kerstin Hoedlmoser 16 ,
• Perrine Ruby 1 ,
• Rebecca M. C. Spencer 17 ,
• Genevieve Albouy 18 ,
• Teodóra Vékony 1 ,
• Manuel Schabus   ORCID: orcid.org/0000-0001-5899-8772 16 &
• Karolina Janacsek 2 , 19   na1  

Nature Reviews Psychology volume  3 ,  pages 123–137 ( 2024 ) Cite this article

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• Human behaviour
• Learning and memory
• Long-term memory

Understanding the complex relationship between sleep and memory consolidation is a major challenge in cognitive neuroscience and psychology. Many studies suggest that sleep triggers off-line memory processes, resulting in less forgetting of declarative memory and performance stabilization in non-declarative memory. However, the role of sleep in human memory consolidation is still under considerable debate, and numerous contradictory and non-replicable findings have been reported. Methodological issues related to experimental designs, task characteristics and measurements, and data-analysis practices all influence the effects that are observed and their interpretation. In this Perspective, we review methodological issues in sleep and memory studies and suggest constructive solutions to address them. We believe that implementing these solutions in future sleep and memory research will substantially advance the field and improve understanding of the specific role of sleep in memory consolidation.

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Acknowledgements

The authors thank K. Schipper for her help and comments on the manuscript. This research was supported by the ANR grant awarded within the framework of the Inserm CPJ ANR-22-CPJ1-0042-01 (to D.N.); Hungary’s National Brain Research Program (project NAP2022-I-2/2022); NKFIH-OTKA PD 124148 (Principal Investigator K.J.); NKFI FK 142945 (Principal Investigator P.S.); Janos Bolyai Research Fellowship of the Hungarian Academy of Sciences (to K.J. and P.S.); and the French National Agency for Research (ANR, grant number ANR-15-CE33-0003, Principal Investigator S.M.).

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These authors contributed equally: Dezső Németh, Emilie Gerbier, Karolina Janacsek.

Authors and Affiliations

Centre de Recherche en Neurosciences de Lyon CRNL U1028 UMR5292, INSERM, CNRS, Université Claude Bernard Lyon, Bron, France

Dezső Németh, Perrine Ruby & Teodóra Vékony

Institute of Psychology, ELTE Eötvös Lorand University, Budapest, Hungary

Dezső Németh, Peter Simor & Karolina Janacsek

Institute of Cognitive Neuroscience and Psychology, Hun-Ren Research Centre for Natural Sciences, Budapest, Hungary

Dezső Németh

Laboratoire Bases, Corpus, Langage (UMR 7320), CNRS, Université Côte d’Azur, Nice, France

Emilie Gerbier

Institute of Medical Psychology and Behavioral Neurobiology, University of Tübingen, Tübingen, Germany

Jan Born & Susanne Diekelmann

Department of Psychology, University of California San Diego, La Jolla, CA, USA

Timothy Rickard

Department of Psychiatry and Psychotherapy, University Hospital Tübingen, Tübingen, Germany

Susanne Diekelmann

School of Psychology, University of Ottawa, Ottawa, Canada

Stuart Fogel

Donders Institute for Brain Cognition and Behaviour, Radboud University, Nijmegen, Netherlands

Lisa Genzel

Institute for Child and Adolescent Psychiatry, Center for Integrative Psychiatry, University Hospital Schleswig-Holstein, Kiel, Germany

Alexander Prehn-Kristensen

Department of Psychology, Faculty of Human Sciences, MSH Medical School Hamburg, University of Applied Sciences and Medical University, Hamburg, Germany

Department of Psychology, University of Notre Dame, Notre Dame, IN, USA

Jessica Payne

Donders Institute for Brain, Cognition and Behavior, Radboud University Medical Center, Nijmegen, The Netherlands

Martin Dresler

Institute of Behavioural Sciences, Semmelweis University, Budapest, Hungary

Peter Simor

Forgetting Team, Centre de Recherche en Neurosciences de Lyon CRNL U1028 UMR5292, INSERM, CNRS, Université Claude Bernard Lyon, Bron, France

Stephanie Mazza

Department of Psychology, Centre for Cognitive Neuroscience, University of Salzburg, Salzburg, Austria

Kerstin Hoedlmoser & Manuel Schabus

Department of Psychological and Brain Sciences, University of Massachusetts, Amherst, MA, USA

Rebecca M. C. Spencer

Department of Movement Sciences, Katholieke Universiteit Leuven, Leuven, Belgium

Genevieve Albouy

Centre for Thinking and Learning, Institute for Lifecourse Development, School of Human Sciences, University of Greenwich, London, UK

Karolina Janacsek

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D.N., E.G., J.B., T.R., S.D., S.F., L.G., A.P.-K., J.P., M.D., P.S., S.M., K.H., P.R., R.M.C.S., G.A., T.V., M.S. and K.J. contributed substantially to discussion of the content. All authors wrote the article. All authors reviewed and/or edited the manuscript before submission.

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Németh, D., Gerbier, E., Born, J. et al. Optimizing the methodology of human sleep and memory research. Nat Rev Psychol 3 , 123–137 (2024). https://doi.org/10.1038/s44159-023-00262-0

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• v.38(1); 2021 Mar

Effects of resistance training intensity on sleep quality and strength recovery in trained men: a randomized cross-over study

Domingo jesús ramos-campo.

1 Faculty of Sports, Catholic University of San Antonio (UCAM), Murcia, Spain

Luis Manuel Martínez-Aranda

Luis andreucaravaca.

2 Chair of Sport Medicine, Catholic University of San Antonio (UCAM), Murcia, Spain

Vicente Ávila-Gandía

3 Department of Exercise Physiology, Catholic University of San Antonio (UCAM), Murcia, Spain

Jacobo Ángel Rubio-Arias

4 LFE Research Group, Department of Health and Human Performance, Faculty of Physical Activity and Sport Science-INEF, Polytechnic University of Madrid, Spain

Resistance training (RT) variables can affect sleep quality, strength recovery and performance. The aim of this study was to examine the acute effect of RT leading to failure vs. non-failure on sleep quality (SQ), heart rate variability (HRV) overnight and one-repetition maximum (1-RM) performance 24 hours after training. Fifteen resistance-trained male athletes (age: 23.4 ± 2.4 years; height 178.0 ± 7.6 cm; weight: 78.2 ± 10.6 kg) performed two training sessions in a randomized order, leading to failure (4x10) or non-failure (5x8(10) repetitions), with 90 seconds for resting between sets at 75% 1-RM in bench press (BP) and half squat (HS). The day after, the participants completed the predicted 1-RM test for both exercises. In addition, the subjective and actigraphic SQ and HRV during sleep were measured after each training session. The day after the training protocol leading to failure, the 1-RM of BP (MD = 7.24 kg; -7.2%; p < 0.001) and HS (MD = 20.20 kg; -11.1%; p < 0.001) decreased. However, this parameter did not decrease after a non-failure RT session. No differences were observed between failure and non-failure training sessions on SQ and HRV; therefore, both types of training sessions similarly affected the SQ and the autonomic modulation during the night after the training session. This study provides an insight into the influence of different training strategies on SQ, strength performance and recovery after moderate- to high-demand training. This information could be useful especially for professional coaches, weightlifters and bodybuilders, due to the potential influence on the programming processes.

INTRODUCTION

Sports performance in individual and team sports is determined by a high demand for maximum strength and power [ 1 ]. Hence, RT has been recommended as the main strategy to stimulate gains in muscle strength, power and muscle mass [ 2 ]. Thus, the optimization of strength training programmes is one of the main interests of researchers and coaches for the improvement of strength and power. Thus, manipulation of strength training variables and, in particular, the intensity of the training loads within a periodized programme, is a key factor to maximize strength training gains [ 3 ]. Several studies have investigated the effect of different training loads on the improvement of strength and power in active young people and elite athletes [ 2 , 4 , 5 ]. In this regard, the effect on hormonal responses, strength, and power muscular gain of training with exercises leading to failure compared to training that does not lead to failure is unclear [ 5 , 6 ].

Training exercises that lead to failure have been defined as the inability to complete a repetition in a full range of motion due to fatigue during workouts [ 5 ], and recently, researchers and coaches have shown an increased interest due to the greater gains in strength and/or power. It appears that training to repetition failure could increase motor unit activation and mechanical stress [ 7 ]. Drinkwater et al. [ 4 ] suggested that strength training that leads to repetition failure could be more efficient than non-failure training in elite junior team sport athletes. However, several studies have shown that training to failure is not critical to achieve significant neural and structural changes to skeletal muscle [ 5 ]. Martorelli et al. [ 6 ] observed that after 10-week RT to failure versus 10-week repetitions not to failure with equalized volume did not provide additional strength and muscle hypertrophy gains in young women. These disagreements of training effects on adaptations could be due to numerous factors related to exercise prescription and training experience Davies et al. [ 8 ] and Mitchell et al. [ 9 ] concluded that acute effects of muscle protein synthetic rates with a lower load lifted to failure resulted in similar hypertrophy as a heavy load lifted to failure. Thus, the differences in the effects of the training with or without leading to failure with a similar volume are not clear. In addition, the effects of training on recovery and sleep quality are a key factor in training adaptations, but to our knowledge, the acute effects of this type of training have not been studied yet.

There is evidence that exercise plays a crucial role as a nonpharmacological alternative to sleep disorders [ 10 ]. Adequate sleep duration and quality are important because they provide a recovery period where metabolic, hormonal and neural adaptations occur [ 11 ]. Several studies have shown that chronic sleep deprivation can lead to a reduction in muscle mass and thus a decrease in muscle strength [ 12 , 13 ]. In this sense, inadequate sleep can lead to a decrease in muscle strength in the post-night session [ 14 ]. Furthermore, sleep, post-exercise recovery and athletic performance seem to be significantly related [ 15 ] and it appears that vigorous exercise can intensify the negative relationship between sleep deprivation and recovery [ 14 ]. In line with this, on exercise days compared to rest days, acute exercise seems to cause earlier rising times and a decrease in the total sleep time. In addition, there is a decrease in the total sleep time on days when the training is more intense. However, changes in rise time, sleep onset latency, sleep efficiency and sleep quality are unclear [ 15 ].

Previous studies focused on studying the relationship between sleep and physical activity, suggesting that the manipulation of training variables could affect sleep quality and recovery, such as intensity of the training or training time [ 16 ]. In this way, Roveda et al. [ 17 ] showed that a single strength session at high intensity is able to improve the parameters related to both the quantity and the quality of sleep, particularly during the first night after exercise. Nevertheless, other authors conclude that exercise intensity and/or duration cause delayed recovery of nocturnal cardiac autonomic modulation, although long exercise duration was needed to induce changes in nocturnal heart rate variability (HRV). Increased exercise intensity or duration does not seem to disrupt sleep quality [ 18 ]. However, no studies comparing these two training types (to failure vs. non-failure) on sleep quality have been found, and the effect that it could have on recovery and HRV is not clear. Therefore, the objective of the study was: to examine the acute effect of RT to failure vs. non-failure on sleep quality, heart rate variability during the first night after the training and the performance at one-repetition maximum (1-RM) in the training session the following day.

MATERIALS AND METHODS

Fifteen male strength-trained athletes participated in this study (23.4 ± 2.4 years; 178.0 ± 7.6 cm; 78.2 ± 10.6 kg). Participants trained between 8.5 and 12 hours per week, with 4.3 ± 2.6 years of experience in strength training including CrossFit or Powerlifting competitions in some cases. All the volunteers signed the informed consent form before enrolling in the study. They received full information about the study purposes and possible risks associated with the training test sessions. The study protocol was approved by the Regional Ethical Review Board and by the University Institutional Research Ethics Committee. Likewise, the research study was conducted in accordance with the recommendations of the Declaration of Helsinki.

Experimental approach

A comparative and randomized cross-over experimental design was used to identify the acute effects of two different resistance-training strategies on the post-24 h 1-RM, actigraphic sleep quality, subjective sleep quality and nocturnal cardiac autonomic activity in trained sports sciences students. Volunteers performed the bench press and squat exercises using two different training sessions based on leading or not leading to failure separated by one week, performing a total of 5 sessions in the laboratory. The velocity-based training (VBT) methodology was used for monitoring all training sessions and tests. In addition, the sleep quality and actigraphy were monitored and evaluated the night after the training session. The next day after each training session, a 1-RM post-test based on movement velocity was performed to determine the changes in that variable.

Subjects performed a pre-programme training session in the laboratory to predict the 1-RM through the mean propulsive velocity (MPV) for two different exercises (bench press and half squat). During the following 2 weeks, the participants completed a total of 4 training sessions, one of them leading to failure (LF) and the other one not leading to failure (NLF), as well as a RM predictive 24 h post-test for each condition. A standardized warm-up protocol was performed (mobility, self-load exercises and several repetitions of the specific exercise with low loads). The order of the conditions (LF-NLF) for each training session was randomized. All sessions were monitored and supervised by researchers specialized in strength and conditioning training. Every session was performed at the same time of day for each individual (± 1 h), under constant environmental conditions (20–22ºC and 60% humidity). In addition, the control criteria for the participating subjects were to maintain a regular diet and hydration and not to ingest caffeine or alcohol for at least 24 hours prior to each training session. A demanding training session during the 48 hours prior to each test was not allowed.

1-RM calculation based on movement velocity

For the predictive RM session, each subject performed a standardized warm-up consisting of joint mobilization and self-load exercises for upper and lower body, with 2 sets of 5 repetitions per exercise (bench press and half squat) performed in the same way with 25–35 kg. Next, the measurements corresponding to load, MPV, calculated% 1-RM, estimated 1-RM, and training load were obtained for each subject for the subsequent training sessions. Participants completed an incremental loading test with the first load set at 18.5 kg (the bar without weights) and, from those starting loads, additional loads were set by adding 10–20 kg increments in each new repetition, with a complete resting time between repetitions. A consensus concerning the loads was agreed between the main researcher and the subject. The bar movement velocity was calculated using a linear encoder (Chronojump, Barcelona, Spain). The squat exercise was performed in a Smith machine (Technogym, Cesena, Italy). The calculated%1-RM and the estimated 1-RM in kg were calculated following the formulas by Loturco et al. [ 19 ] for the squat exercise and Jidovtseff et al. [ 20 ] for the bench press. The full repetition for achieving the nearest value to the 100% 1-RM with proper lifting by the subject was selected in order to establish the training load for the following sessions. In addition, both the 1-RM predictive tests (pre and 24 h post) were calculated using a two-point method as described in previous investigations [ 21 , 22 ].

Training sessions

After the 1-RM testing session, the participants performed four different sessions divided into two different blocks and in a randomized order, separated by a minimum of 72 h during the following weeks. (1) Strength training session predicting the 1-RM through the two-point method (50–80%) in both exercises, followed by one of the following routines: a) routine leading to failure in the last repetition composed of 4x10 repetitions, 90 s for resting between sets at 75% 1-RM in two different exercises (bench press, monitoring MVP at 0.53–0.55 m/s; and half squat at 0.75–0.76 m/s); b) routine not leading to failure composed of 5x8(10) – 2 repetitions in reserve, 90 s for resting between sets at 75% 1-RM in the same exercises (bench press and half squat) [ 23 ]. (2) The day after, the participants completed the predicted 1-RM test using the two-point method for both exercises. (3) One week later, the participants performed a strength training session predicting the 1-RM using the two-point method for both exercises, followed by the opposite routine of the one performed the previous week (4). The next day, the participants completed the predicted 1-RM test measured by the two-point method for both exercises ( Figure 1 ). All the tests and training sessions (routines focused on sets and repetitions) were monitored through the bar movement velocity using a linear encoder.

Experimental design and testing procedures.

Actigraphic sleep quality, subjective sleep quality and nocturnal cardiac autonomic activity

The actigraphic sleep quality and nocturnal cardiac autonomic activity (HRV) during sleep were measured after each training day (sessions 1 and 3), with a previous period of instruction to the participants. The actigraphic sleep quality was recorded using an Actiwatch activity monitoring system (Cambridge Neurotechnology, Cambridge, UK) which measures activity through a piezo-electric accelerometer. Each participant’s non-dominant wrist movement was monitored. A low threshold of actigraphic sensitivity was selected (80 counts per time period) and the data recorded by the actigraph were analysed with the Actiwatch sleep analysis software.

Data analysis started with the onset of nocturnal rest (bedtime) and ended with the onset of daytime activity (wake time). The following sleep parameters were measured: (I) sleep efficiency (%): percentage of time spent asleep; (II) time in bed (min); (III) actual sleep time (min); (IV) actual wake time (min); (V) number of awakenings; and (VI) average time of each awakening (min).

Along with the actigraph, during the night each subject wore an H7 strap Heart Monitor (Polar Electro, Kempele, Finland) to assess HRV. Variables of cardiac autonomic activity were analysed during the 4-hour sleep period that began 30 minutes after bedtime [ 18 ]. The R-R series were analysed using Kubios HRV software (version 2.0, Biosignal Analysis and Medical Imaging Group, University of Kuopio, Finland).

The following HRV variables were evaluated: (I) ratio of low frequency (LF) to high frequency (HF) band; (II) total power (TP); (III) percentage of differences between adjacent normal R-R inter-vals > 50 ms (pNN50); (IV) square root of the mean of the sum of the squared differences between adjacent normal R-R intervals (RMSSD); (V) standard deviation of all NN normal intervals (SDNN); (VI) mean heart rate; and (VII) R-R mean intervals.

In addition, the participants were instructed to assess the subjective sleep quality in the morning after waking up using the Karolinska Sleep Diary (KSD) [ 24 ], which addresses the following points: (I) sleep quality; (II) sleep comfort; (III) ease of falling asleep; (IV) awakening; (V) ease of waking up; (VI) feeling of rest; (VII) Did you have enough sleep?

Statistical analysis

Statistical data analysis was performed with SPSS software (SPSS 21.0, IBM Corp.) for Windows. For inferential analysis, the Shapiro–Wilk W-test was performed to establish the normality of the sampling distribution, and Mauchly’s W-test analysed the sphericity between measurements. Moreover, analysis of variance for repeated measures (ANOVA) was calculated (general linear model) to analyse the effects of load training (failure versus not to failure) as well as Bonferroni-adjusted pairwise comparisons on 1-RM test. In addition, a t-test or the nonparametric equivalent (Wilcoxon test) was performed to analyse the effect of the session training on HRV and sleep quality. The effect size was calculated using partial eta-squared ( η2p) for variance analysis. Values of 0.01, 0.06, and above 0.14 were considered as small, medium, and large, respectively. Cohen’s d was used to show the standardized difference between two means. Threshold values for ES were ≥ 0.1 (small), ≥ 0.3 (moderate), ≥ 1.2 (large), and ≥ 2.0 (very large) [ 25 ]. The level of significance was set at p ≤ 0.05.

Table 1 provides the main effects obtained from the ANOVA analysis for 1-RM test performance. Main effects significant on Time and Time*Group were observed on 1-RM of BP and HS test.

Main effects of ANOVA analysis for 1RM test

Note: BP: bench press; HS: Half-Squat

The analysis of the pair comparison ( Table 2 ) showed a significant decrease after the session to failure in the 1-RM test of the exercises of BP (mean difference = 7.24 kg; p < 0.001; d = 1.00) and HS (mean difference = 20.20 kg; p < 0.001; d = 1.43). In addition, differences between sessions were observed in 1-RM of BP (p < 0.001; d = 0.92) and HS (p = 0.03; d = 0.66).

Pair comparation on performance after Failure and Non-Failure sessions

Note: For the Student t-test, effect size is given by Cohen’s d; for the Wilcoxon test, effect size is given by the matched rank biserial correlation; BP: bench press; HS: half-squat; SD: standard deviation; CI: confident interval.

Table 3 shows the summary statistics for heart rate variability during the night and Table 4 compares the effects of sessions on sleep quality. No significant differences were observed between failure and non-failure sessions in any variable analysed in Tables 3 and ​ and4 4 .

Heart rate variability results

Note: SDNN: standard deviation of all normal NN intervals; HR: mean heart rate; RMSSD: square root of the mean of the sum of the squared differences between adjacent normal R-R intervals; pNN50: percentage of differences between adjacent normal R-R intervals > 50 ms; AR: autoregressive; LF: low-frequency; HF: high-frequency; SD: Standard Deviation; CI: Confident Interval

Sleep quality results after each session

Note: SD: standard deviation; CI: confident interval; ES: effect size.

This study aimed to analyse the acute effect of RT to failure vs non-failure on sleep quality, heart rate variability during the night and the strength performance (1-RM) one day after the training session. The results revealed that a single RT session leading to failure produces fatigue that decrease the 1-RM in bench press (7.2%) and half-squat (11.1%) on the following day. However, this parameter did not decrease after an RT session, with an intensity with two repetitions in reserve. In addition, to the best of our knowledge, this is the first study which analyses the effect of RT on sleep quality and, notably, in resistance-trained athletes. The results showed that both types of training sessions (failure and non-failure) had a similar effect on the sleep quality and quantity, perceived and measured by the questionnaire and actigraphy, as well as on the autonomic modulation during the night after the training session.

Several studies have analysed the time course of recovery following RT leading or not to failure [ 26 – 28 ], reporting that non-failure RT seems to speed up the recovery processes between 24 and 48 hours compared to training to failure. These findings are in accordance with the results of the present study, since we did not observe any changes in the values of bench press and half-squat strength performance (measured by 1-RM) 24 hours after non-failure session training. On the other hand, a significant decrease of 7.2% in bench press and 11.1% in half-squat was found 24 hours after RT to failure and is in accordance with the results reported by MoránNavarro et al. [ 28 ] in the attained velocity against the load that elicited 1 ms -1 and 75% of 1-RM loads in the same exercises. One possible reason for these findings may be related to the slow recovery of metabolic and hormonal homeostasis after training to muscle failure. Previous studies reported higher acute fatigue, determined by the levels of biochemical and hormonal markers (ammonia, GH, testosterone, cortisol, etc) and higher levels of muscle damage markers (creatine kinase – CK) after RT to failure. Consequently, RT to failure increases the amount of time needed for recovery and it could affect the volume of training, which is the most important factor to develop muscle mass [ 29 ]. In addition, non-failure training would be an especially interesting method in sport modalities in which there is a necessity to develop simultaneously strength, endurance and technical capacities due to its faster time course of recovery [ 30 ].

Sleep is considered the most important method for recovery from daily load [ 31 ] assisting in the recovery of the nervous and metabolic cost imposed by the waking state [ 32 ]. A good sleep is vital in the regulation of hormone secretion and in the restoration of metabolic processes in athletes [ 33 ]. Therefore, sleep problems can affect the recovery process and future physiological adaptations in the training process. In this way, sleep disturbance in athletes can impair glycogen re-synthesis and muscle damage repair, and it can also increase the mental fatigue and produce cognitive function impairment [ 16 ]. Specifically, some studies found that vigorous exercise, especially when performed close to bedtime, may impair sleep behaviour [ 34 ]. However, other studies reported that high-intensity training does not disrupt and may even improve subsequent nocturnal sleep when it is performed in the early evening [ 35 ]. Particularly, our results showed that both types of RT sessions produce the same effect on sleep quality and quantity. These findings agreed with the previous quantity range of 7–9 h of sleep per night recommended by the National Sleep Foundation for Healthy Sleep [ 36 ]. In addition, our participants reported 3.6/5 (failure session) or 3.9/5 (non-failure session) points in the first item of the KSD, which analysed the subjective sleep quality. Moreover, the sleep efficiency measured by actigraphy was 89% in both cases, leading to good values of sleep quantity and quality. Notably, although poor recovery processes that affected strength performance were reported after RT to failure, they did not seem to have an effect on the sleep quality.

Even though a similar sleep response was found after both types of RT session (failure vs non-failure), athletes did not obtain the same level of recovery 24 hours after the exercise, obtaining lower strength performance. As we explained above, these findings could be related to higher neuromuscular fatigue and muscle damage after a failure session [ 28 ], indicating that participants did not obtain total recovery and the same strength values as after a non-failure session. Also, fatigue factors (e.g. muscle damage or biochemical markers) may have a greater influence on strength performance than sleep quality. However, in most of the previous studies which analysed the effect of exercise on sleep quality, endurance training [ 16 , 31 , 35 ] was performed, or the subjects were older in those cases where they studied the effect of RT [ 37 ]. Therefore, it is necessary to continue analysing the effect of RT on sleep quality because previous studies found that lower sleep quality is related to higher prevalence of sarcopenia [ 38 ] and inadequate sleep impairs maximal muscle strength and muscle growth [ 14 ].

Concerning HRV variables, the sleep quality results reported in our study were in line with those obtained for HRV variables. Thus, both types of training sessions (failure and non-failure) stimulated the same autonomic response during sleep. However, there are no previous studies in analysing the effect of RT session on HRV during night sleep. Our HRV results are in accordance with some previous studies using endurance training sessions, reporting that late night moderate or high intensity training did not disturb the cardiac nocturnal modulation [ 16 , 31 ] and that the changes in HRV observed after exercise return to baseline after 5–15 min [ 39 ]. In addition, it is known that the fitness status affects parasympathetic recovery, showing that highly trained athletes were characterized by rapid recovery of parasympathetic balance after exercise [ 40 ]. Thus, the fitness level of the sample of the current study (i.e., highly trained resistance-trained athletes) may have an additional effect on the cardiac autonomic modulation result. From an applied perspective and, considering that a recent study reported that RT-LF and RT-NLF are similarly effective in promoting increases in muscle mass [ 41 ], strength conditioning specialists and athletic coaches should consider that athletes performing an RT session leading to failure will suffer from higher immediate fatigue and they will need a longer time in order not to compromise the recovery processes (≥ 48 h) in comparison to a non-failure RT session. This fact must be taken into consideration if athletes want to increase their training frequency in order to increase the training volume too.

Finally, this study has some limitations, since we did not include a control night in order to compare the results of sleep quality after training with one rest day. In addition, the sample size is limited and, for this reason, our results cannot be extrapolated to other types of resistance training (circuit training, cluster, and so on); nor can our findings be generalised to other athlete modalities (e.g., team sport athletes, endurance athletes, …) or gender (female athletes).

CONCLUSIONS

In conclusion, a single session of RT to failure produced fatigue that decreased the 1-RM in BP (7.2%) and HS (11.1%) on the following day. However, this parameter did not decrease after a non-failure RT session. In addition, both types of acute training sessions (failure and non-failure) seem to have affected in a similar manner the perceived and measured sleep quantity and quality as well as the autonomic modulation during the night after the training session.

Acknowledgments

There is no financial support for this project. No founds were received for this study from National Institutes, Welcome Trust, University or others. The authors thank to all the participants in this study and G. Sanz for the help in the proofreading process.

Conflict of interest declaration

No conflicts of interest, financial or otherwise, are declared by the authors.

CITATION: Ramos-Campo DJ, Martínez-Aranda LM, Andreu-Caravaca L et al. Effects of resistance training intensity on sleep quality and strength recovery in trained men: a randomized cross-over study. Biol Sport. 2021;38(1):81–88.