The Controversy over CIO

Sit down and cuddle up under a cozy blanket because this post is a long one!

Controversy accompanies any possible parenting decision, as is quickly evident if you read comments on a parenting article or even in mom groups on Facebook. There is always more than one way to do things, and it’s incredibly easy to believe your way is the right way.

One of these controversial parenting decisions is whether or not to sleep train babies and children. And if sleep training itself is even acceptable, what methods should (or shouldn’t) be used is next on the list of controversy.

Researchers and parents in favor of sleep training – even methods which allow for the child to cry – advertise the benefits for both parent and child. Children who are sleep trained are given the opportunity to learn skills like self-soothing and sleeping through the night, while their parents also get to benefit from a full night’s sleep, as well as peace of mind surrounding bedtime. On the other hand, those who oppose sleep training worry about the long-term effects for the emotional well-being of a child who is left alone to cry. They claim that the elevated stress levels of a crying baby can cause permanent detrimental changes to a baby’s brain, and they worry about how letting a child cry alone might affect the parent-child relationship.

So who is right? I researched the research, and here’s what I found.

There are a lot of opinions and research out there about the acceptability of sleep training and especially about letting your baby "cry it out." So I researched the research and my findings are in this blogpost. **Spoiler alert: the side effects of letting your child CIO are that your child will likely learn good sleep habits and they'll keep loving you during and after the sleep training process! Win-win!

Anti Sleep Training Studies and Articles


“The Effects of Excessive Crying” by Dr. William Sears

This article begins by explaining that when babies cry, they experience panic and anxiety and their bodies are flooded with stress hormones. It goes on to address many of the negative side effects of leaving a baby to “endure many nights or weeks of crying-it-out alone.” Some of the cited effects are chemical and hormonal imbalance in the brain; decreased intellectual, emotional, and social development; and harmful physiological changes.

However, upon further investigation into the studies cited in the article, I found that the studies aren’t actually based on letting your child cry it out as a method of sleep training. One of Sears’ examples is that, “Researchers at Pennsylvania State and Arizona State Universities found that infants with excessive crying during the early months showed more difficulty controlling their emotions and became even fussier when parents tried to console them at 10 months.” But this was a study about colic, and the sleep habits of the babies involved were not even examined. The study simply indicates that children with colic might take more time to learn how to handle their emotions than babies without colic. Even if the sample size is large and the age group includes human infants, the study is not relevant to the effects of using cry-it-out as a sleep training method. Other studies referenced in this article have the same problem of not actually being studies about sleep training.


“Dangers of ‘Crying It Out’” by Dr. Darcia Narvaez

This article delineates how dangerous it is to let your baby cry it out because that sort of distress “is a practice that can damage children . . . in many ways for the long term.” To illustrate, Narvaez points to a study on rats. The study says that rats who have low-nurturing mothers in the first 10 days of life end up experiencing anxiety towards new situations for the rest of their lives.

While I am not particularly opposed to using studies on animals to predict how certain actions will affect humans, I am opposed to using non-parallel studies. Narvaez specifically mentions that 10 days for rats are equivalent to six months for humans. In order for the study to predict effects for human children, parents would have to be low-nurturing toward their babies for six months. Sleep training involving cry-it-out methods typically lasts no longer than two weeks, and even during the sleep training, parents surely give their children love and attention during the appropriate hours that the baby is awake. Parents who sleep train should not automatically be assumed to be low-nurturing parents. On the contrary, most parents who sleep train do so because they recognize the importance of healthy sleep habits for their child.


“Why Cry-It-Out Can Be Bad for the Brain” by Kathleen Kendall-Tackett

In this article, Kendall-Tackett posits that “sleep training and cry-it-out parenting techniques are potentially damaging to long-term mental health.” The information she uses to support her theory is based on previous work of hers relating to the long-term effects of childhood abuse. In her work on child abuse, she found that, “Persons who have experienced traumatic events are often ‘primed’ to over-react to subsequent stressors, making them more vulnerable to these events.” She claims that chronic childhood stress changes brain chemistry and greatly contributes to health problems as an adult.

What is perplexing about this article is that it is not based on a specific study of sleep training, but rather, the author clearly mentions that her work was based on a review of many child-abuse cases. Informed sleep training in a loving environment is not child abuse. The “traumatic” part of sleep training is very brief (roughly two weeks in nearly every instance) and is sandwiched between many daily loving interactions.

Interestingly enough, she takes the time to mention that “milder forms [of sleep training] will probably not cause any long-term harm if they occur in the context of overall responsive parenting.”


Pro Sleep Training Studies and Articles


Behavioral Interventions for Infant Sleep Problems: A Randomized Controlled Trial

This study aimed to determine whether different methods of sleep training helped with sleep problems. Additionally, the study aimed to find out how these sleep training methods affected parent and infant stress, emotional/behavioral problems in the infant, and parent-child attachment.

Infants were randomized into three groups: graduated extinction, bedtime fading, and a sleep education control group (this group was just provided with general sleep information).

Parent stress was measured using self-reporting at various times throughout the study, and infant stress was measured by determining salivary cortisol levels in the morning and afternoon following a sleep training night. Emotional/behavioral problems were also measured by a parent report. Parent-child attachment was measured according to certain criteria, using standardized interactions between the parent, child, and a stranger.

The study found that both groups that used a specific sleep training method manifested in sleeping improvements for the infants involved, above the level of the control group. Additionally, they found no detrimental effects on parent or infant stress, emotional/behavioral problems, or parent-child attachment for the sleep trained group.

The sample size for this study was 43 infants, which isn’t a huge sample, but it is enough for a basic overview. Data was collected via parent reports of specified information, which was gathered at home. On the one hand, parent reports can be inaccurate if the parent chooses to falsely portray success, but on the other hand, parent reports can also be the most accurate since parents are organically in the home environment and can therefore best discern how any implemented changes affect the infant and home overall.


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

The objective of this study was to determine whether sleep training had long lasting effects, whether negative or positive.

The specific methodology was not given in the abstract that I found, so only basic information was available. The study looked at child mental health, sleep, psychosocial functioning, and stress regulation; the child-parent relationship; and maternal mental health five years after the initial sleep training was administered.

After their tests, they concluded that there were no long-lasting effects – positive or negative – to those children who had received sleep training as infants. They took this as a sign that it’s okay to go ahead with sleep training since that can reduce the burden of infant sleep problems and maternal depression.

The sample size for this study was 326 human children. The age of the children at the time of sleep intervention was eight to ten months old, while the study took place five years later. Of the infants surveyed, about half had received sleep intervention, while the other half had not (control group). This is quite a large sample, which makes the conclusion more convincing.


“The Ferber method: What does the evidence tell us about "cry it out" sleep training?” by Dr. Gwen Dewar

Dewar begins this article by saying that experts can agree that “studies leave important questions unanswered.” There are many variables when doing sleep training studies, and it’s hard to truly isolate cry-it-out methods to determine what the effects actually are. When studies are done, it’s impossible to know whether parents have followed the outlined behavior with exactness, as well as how families that dropped out of the study may have biased the results. It’s also difficult to determine what other factors might be influencing the results since all families are different, and long-term outcomes are difficult to measure with objectivity.

She goes on to list some arguments that support the Ferber method (timed checks), such as fewer bedtime tantrums and greater ability to settle down quickly at night. She also shares arguments against the method, including that leaving our children to cry “seems to violate our deepest instincts” and babies may still be distressed even after they’ve stopped crying.

Finally, she lists alternative sleep training methods (“positive routines with faded bedtime” and “extinction with parental presence”), and refers to a study that says there are “no significant differences in treatment outcomes” for any of the three methods mentioned, meaning that one training method is not better than another – you simply choose one that works for you and remain consistent until you get your desired results.

This article falls in line most with my own thoughts about cry-it-out studies, as Dewar basically claims that it is impossible to do an effective study due to all the possible variables. She takes a mostly objective approach, clearly stating the facts about both sides with little bias. She seems to be in favor of sleep training, though perhaps wary of letting a baby “cry it out” alone as a means for sleep training.



Controversy arises when answers are not black and white, so it is easy to see why there is controversy over sleep training. Everyone may be able to agree on the importance of both healthy sleep and emotional wellness for babies. However, people have a difficult time agreeing on what responsible parenting looks like and what the long-term results of certain methods of sleep training might be.

As I mentioned above, I agree with Dr. Dewar that doing a perfect study on sleep training would be incredibly difficult. However, the studies I found in support of sleep training actually used sleep training as part of the study, which tells me that, although imperfect, those results reveal some true information about sleep training and its effects. The studies I found in opposition to sleep training, on the other hand, were misleading because none of them were actually based on sleep training. Those studies were based on colic, low-nurturing rat mothers, and child abuse. While colic, low-nurturing mothers, and child abuse would all definitely affect sleeping habits and the emotional wellbeing of a child, none of those things could be categorized as “sleep training.”

What critics of sleep training need to remember (or perhaps learn), is that sleep training – even using cry-it-out methods – does not mean endlessly leaving your child to cry for weeks, months, or years. Sleep training lasts a short period (usually two weeks if done correctly), and during the sleep training, there is still love, comfort, and connectedness between parents and their children. In my opinion, and based on the lack of evidence to the contrary, a few hours of crying alone over two weeks’ time will not cause short- or long-term damage of any kind to a child. The child may experience some stress and sadness in the crying times, but those are emotions people go through all the time when they're learning hard things. Those feelings will pass like any other emotion, and the result will be a child who learns how to fall asleep and stay asleep without relying on a parent. Then, both children and parents who are well-rested will be much more able to handle the everyday stresses they encounter.

What proponents of sleep training need to do is to make sure that they’re informed about whatever method they’re choosing to use – for example, letting your baby cry it out does not mean putting them in their crib and letting them cry for three hours at naptime.

There will always be controversy over sleep training, so in the end, parents need to choose a method that works for them. However, more information and a more thorough investigation of some of the studies and facts that exist make it easier for parents to make an informed decision.


Personal experience

I used CIO with my own daughter, and though it was difficult to endure, I cannot deny that she quickly learned to fall asleep on her own, sleep through the night, and sleep at least one hour at each naptime using this method. Not only did she learn these essential sleeping skills, but she kept loving me throughout the process, and she still loves me today. 

My goal was not to “make her cry,” but rather to “teach her to sleep,” and I was successful with that goal: she’s been sleeping like a champ for the majority of her life thanks to sleep training. Her good sleep then enables me to be a much more sane and capable parent when those inevitable toddler tantrums occur ;)