You’ve probably heard the claim that sleep training—especially methods like “cry-it-out”—can flood babies with toxic stress. But is that actually what the science says? In this episode, I sit down with a leading developmental expert to unpack the research on cortisol, stress, and infant development. We cover how the stress response system works, what truly qualifies as toxic stress, and why common fears about sleep training may be missing important context. Whether you’re team sleep-train or not, this episode offers clarity, compassion, and evidence-backed guidance.

Key Takeaways:

• Cortisol is a normal, necessary hormone that helps us respond to stress.

• Not all stress is toxic—especially when it’s brief and supported by a caregiver.

• There’s no evidence linking sleep training with long-term harm.

• Misinterpreting small or flawed studies can create unnecessary fear for parents.

• Sleep training, when developmentally appropriate, can be a positive and adaptive experience for both babies and parents.

00;00;00;04 – 00;00;23;26

Dr. Mona

Hello, it’s Doctor Mona and you’re listening to the follow up. The only part of your Monday that won’t involve a tantrum or a snack negotiation. Or someone yelling your name from the bathroom. Today’s episode is the one you send to every person who says sleep training is harmful because cortisol. We’re breaking down the stress hormone that gets a bad rep online, but is actually vital to development.

 

00;00;24;03 – 00;00;45;25

Dr. Mona

My guest, doctor Brie Reid, who holds a doctorate in developmental psychology, helps us unpack the difference between toxic, tolerable and normal stress. Plus, she sets the record straight on that one infamous and deeply flawed cortisol sleep training study. And yes, I sleep train both of my kids full cry it out with my son. And by the way, he’s securely attached, emotionally intelligent and thriving.

 

00;00;45;25 – 00;01;08;05

Dr. Mona

Thank you very much. And a little further finesse during regressions with my daughter. She didn’t need sleep training to get to 12 hours, but when the wheels came off, she needed some guidance during those regressions. That’s real life. This isn’t about guilt. It’s about science, sanity, and doing what works for your family. If sleep training, crying included, is your cup of tea, and even if it’s not, it’s still important.

 

00;01;08;05 – 00;01;15;23

Dr. Mona

We don’t spread misinformation. Let’s get to it.

 

00;01;15;25 – 00;01;34;08

Dr. Mona

So you you’re a lot of your research looks at cortisol, which obviously for anyone who’s listening. Cortisol is, stress hormone. That is good in some amount. But obviously in toxic amounts or large amounts, it can be detrimental to the the developmental system. So tell me more about this concept of cortisol and how it impacts development.

 

00;01;34;10 – 00;01;55;18

Dr. Brie Reid

Yeah. So I’m so glad you asked because I think this is a huge misconception. Just everywhere for parents and non-parents alike about cortisol and stress. So I love what you said about good in little amounts, maybe not so much in toxic amounts because, it is a hormone created by our body that really helps us in day to day life.

 

00;01;55;19 – 00;02;15;28

Dr. Brie Reid

It rises when we wake up in the morning to help us wake up and go look for food. And then before we go to sleep, it falls to help us kind of fall. And it follows a daily rhythm. And it also helps us respond to threat. So, no human in the history of ever has ever experienced no stress or no threat in their life.

 

00;02;15;28 – 00;02;40;07

Dr. Brie Reid

So it’s wonderful that, you know, we’ll say the unscientific term of Mother Nature provided us with, a system to help respond to that, and to kind of mobilize our body’s resources to respond to threats. We often think of it in terms of a fight or flight response. And, so cortisol is there’s two parts of that response.

 

00;02;40;07 – 00;03;08;28

Dr. Brie Reid

The first response is what we know as adrenaline. Right? Our heart’s racing, our hands are shaking. And then cortisol is a product of, the hypothalamic pituitary adrenal cortical system, which we won’t get into in detail, but it’s just with stress, what we consider the stress response system, that produces cortisol, that helps us kind of maintain our response to a little more of a chronic threat, that we experience over a longer period of time.

 

00;03;08;28 – 00;03;29;12

Dr. Brie Reid

So we’re adrenaline is a few minutes. Cortisol is kind of more of like the 20 minutes to a couple of hours sort of response. And the really cool thing about it is that it helps change our brains. It kind of helps signal our brains to help us respond to a similar threat. The next time we experience it.

 

00;03;29;14 – 00;03;57;07

Dr. Brie Reid

But what makes it tolerable is that there is, an attachment figure, a caregiver in their life that can care for them and help their body and brain learn. Okay, I’m still safe. Scary things can happen. I’m still safe and kind of help that stressor response regulate and down regulate after experiencing a stress like that. So it’s kind of a time limited stress and it’s buffered by an adult.

 

00;03;57;09 – 00;04;16;27

Dr. Mona

Look there are many methods of sleep training. And I in my training in in residency, I actually didn’t get a lot of sleep training and residency was my first job that actually, you know, my mentor there taught me a lot about sleep training, and that’s when I kind of created my own practice on how I looked at sleep and, you know, infant sleep, toddler sleep.

 

00;04;16;29 – 00;04;37;03

Dr. Mona

In terms of the research, though, would you say, I mean, in general is if a family does decide to use a cried out method and maybe they don’t want to, and I’m 100% okay with that. That is obvious. Is that considered an early life stress that would be impacting their development? Because I know there’s a lot of, negativity around cried out methods, but what would the research kind of show?

 

00;04;37;03 – 00;04;39;17

Dr. Mona

Is there just not enough research? Like you said?

 

00;04;39;20 – 00;05;03;11

Dr. Brie Reid

So a few things for from my personal opinion. No, I would not consider that a toxic stressor. I don’t know that I would even consider it a tolerable stressor. Right. I wouldn’t consider it on the level of losing a loved one or losing a limb. That needs buffering from a supportive caregiver. I would consider that probably a positive stress response.

 

00;05;03;11 – 00;05;27;13

Dr. Brie Reid

There’s probably a stress response because an infant at that time is learning how to self-regulate and learning the skill of putting themselves to sleep. And so, in the interest of full disclosure, we just finished sleep training my daughter and, you know, she we started that at around five months when it was clear that she was developmentally ready.

 

00;05;27;13 – 00;05;51;19

Dr. Brie Reid

And, it was, you know, picking her up and intervening in her sleep is actually making her more upset. She wanted the opportunity to try to figure it out on her own, and she wasn’t ready before, you know, she was probably ready. She probably could have been ready at around, like, maybe a little before that. But, you know, five months seemed to work for her.

 

00;05;51;19 – 00;06;12;00

Dr. Brie Reid

And there might be individual differences there. So I don’t consider it a toxic stress. I’ve done it with my child. It is difficult as a parent to hear your child cry. I’m not going to lie. And say that it wasn’t. You know, we were kind of sitting in the basement waiting and it’s like, wow, it’s very difficult to hear your child cry.

 

00;06;12;00 – 00;06;36;13

Dr. Brie Reid

And this is a normal physiological response because I’m a functioning human who just as a child. And of course, of course, we are adapted to respond to a child. And we’re also adapted to let the child, when developmentally appropriate, you know, build their skill set and different things like self-regulation and putting themselves to sleep. And that’s a huge skill.

 

00;06;36;19 – 00;07;05;08

Dr. Brie Reid

Putting themselves to sleep is a huge skill development, especially in that first year. So from the research, as you could probably tell our listeners, there have been no studies that have found negative long term effects from sleep training methods. And I think every parent needs to find their own level of comfort. You know, it’s usually a parent distress that really predicts what sleep training about that they do.

 

00;07;05;10 – 00;07;22;24

Dr. Brie Reid

You know, for us, we didn’t want to just like close the door and walk away for 12 hours. That didn’t feel right to us, but I don’t it didn’t feel wrong to us because we thought, oh, this will damage your child. It was just distressing for us to do that. And so we kind of did a graduated extinction approach.

 

00;07;22;26 – 00;07;50;24

Dr. Brie Reid

And for a cortisol perspective, I think from what I see in parenting boards and the internet, which I try to avoid in general when looking for parenting advice and interpretations of the scientific literature, I see people reference two kinds of studies to support the claim that cry it out is damaging children and the level of toxic stress to their brain.

 

00;07;50;27 – 00;08;27;03

Dr. Brie Reid

So the first uses one study on cortisol that was done in a very small population of children. And I would say that the methods used in that study were inappropriate and the conclusions drawn were misleading. As the study is written in its current form and the second part is inappropriately using studies of the previously institutionalized children who spent their infancy in orphanages and around the world, and using that as a way as like, an analogy for this is cry it out.

 

00;08;27;03 – 00;08;50;20

Dr. Brie Reid

And so I’ll start with the first study that is referenced. This is the only study that I know of that really looks at a cry it out in cortisol together. There really don’t seem to be that many studies, probably because long term studies have found no negative impacts of of cry it out or of sleep training methods for children’s development.

 

00;08;50;22 – 00;09;13;22

Dr. Brie Reid

And so it would be very difficult to secure funding from the government to say, let’s look at cortisol when there are no negative side effects, because we don’t need to see the mechanism there when there aren’t negative outcomes. So, the first study is by Middlemiss and other colleagues and I believe she’s, oh, maybe at UT Austin or something.

 

00;09;13;22 – 00;09;44;14

Dr. Brie Reid

I’m not sure. But the study was done in 25 mother infant pairs. There was no control group, so there was no group of children who weren’t undergoing sleep training. And, this is the way that the study did their cortisol research is just not how we conduct high quality cortisol research. For one, you need to have a baseline measure of what is normal in a normal day.

 

00;09;44;14 – 00;10;05;12

Dr. Brie Reid

What is the level of cortisol. Because again, there are individual differences. What might be high for me might not be high for you. And what be what might be normal for me might be low or high for you. And so we always need to know, okay, what where is that individual’s baseline? This study didn’t have that for either the mothers or the children.

 

00;10;05;14 – 00;10;34;07

Dr. Brie Reid

They just said children exhibited high cortisol, but didn’t really give us the what that was and didn’t really characterize it as a response, you know, from their normal levels. And that’s challenging. For one, there’s timing issues. There was no information about whether or not mothers breastfed their infants right before cortisol was collected, because cortisol passes through breast milk is a normal part of what our systems do.

 

00;10;34;07 – 00;10;58;22

Dr. Brie Reid

Not that that’s bad. But that could influence the cortisol levels and saliva. And then, you know, the statistical analyzes performed were incorrect based on the methods. There’s a huge amount of missing data. So they started with 25 infant pairs. And then by the end of the study, they only they made their conclusions based on ten infants, which is not a lot of infants to go off of.

 

00;10;58;22 – 00;11;25;12

Dr. Brie Reid

If you really want a larger sample of infants to understand, okay, what’s normal for a population? Because, you know, you could ask ten parents and you get answers all over the board, right? What? Yeah. What worked for them, what’s stressful, etc.. And so because of all of these methodological questions that come up from this one study, it just makes interpretation of her findings and conclusions really impossible.

 

00;11;25;12 – 00;11;47;23

Dr. Brie Reid

And so I would not use this study as a way to say it’s either good or bad. Because really, when I read the study, I say, we don’t know and there’s not enough information. And I would point to the other studies on sleep training. So the other set of science that people reference is the studies of children growing up in institutional care or orphanage care as infants.

 

00;11;47;23 – 00;12;20;19

Dr. Brie Reid

And this context is not the same as your infant going to sleep in their crib with you as a caregiver day after day, night after night. The levels of psychosocial and cognitive deprivation in these institutional contexts are very severe. And there is, you know, the caregivers in these situations are obviously paid not well, they’re trying their best, but it’s really an impossible task of caring for, you know, 12 to 20 infants at a time.

 

00;12;20;19 – 00;12;44;17

Dr. Brie Reid

You know, you really have to systematize the process. And it’s kind of, it’s just it’s not the kind of responsive caregiving that we would anticipate. And so these children often just don’t get the kind of stimulation either from their physical environment or from their social environment that we know that children need in order to develop and thrive.

 

00;12;44;17 – 00;13;35;01

Dr. Brie Reid

And so as a response, yes, or cortisol increases initially and then it becomes downregulated because their body says, oh, there’s too much stress in this environment to handle. And too much cortisol is toxic. And so I’m going to down regulate it way below normal. Because I can’t afford to keep mounting this stress response. And that’s, those outcomes from those children that we see, you know, behavior issues kind of, externalizing or aggression issues or kind of like ADHD symptoms, really indications that they’re not really able to regulate their emotions and that, again, when you have a supportive caregiver, it’s just a very different context from institutional care.

 

00;13;35;01 – 00;14;02;26

Dr. Brie Reid

And I cannot emphasize that enough that the levels of toxic stress that these children experiences in the institution are without, that caregiver support, without that buffer. And just like totally different from the normal human infant, the adult relationship that we would expect. So that’s why I don’t from the literature. I don’t think that from my opinion, cry it out.

 

00;14;02;26 – 00;14;27;28

Dr. Brie Reid

Methods of sleep training or sleep training in general is a negative thing. I actually think that it can be very positive depending on the family context. It can reduce rates of maternal and paternal depression and really help caregivers be there, fully responsive selves for the infant. Very difficult to, you know, operate on sleep deprivation for multiple years or months at a time.

 

00;14;27;28 – 00;14;49;05

Dr. Brie Reid

And so, yeah, the child, the opportunity to learn how to put themselves to sleep and cycle through those more adult patterns of sleep can be really adaptive for them, because more sleep is great for children, linked to a lot of positive outcomes and really good for adults.

 

00;14;49;08 – 00;15;10;19

Dr. Mona

And that’s your follow up. Just a small dose of the real relatable and eye opening conversations we love to have here. If you smiled, nodded, or had an moment, go ahead and download, follow and share this episode with a friend. Let’s grow this village together for more everyday parenting wins and real talk. Hang out with us on Instagram at the PedsDocTalk podcast.

 

00;15;10;26 – 00;15;26;08

Dr. Mona

Want more? Dive into the full episode and more at Pedsdoctalk.com. Because parenting is better with support. And remember, consistency is key. Humor is medicine and follow ups are everything. I’m Doctor Mona. See you next time for your next dose.