Look, I'm about to tell you something you probably already know, but I want you to stick with me. Rest, you know, the act of slowing the motors, decreasing the daily surge, shutting down the auxiliary machinery of our bodies and brains, is so important. For many of us it's the only way to get a reprieve from the relentless stress we regularly endure. So, yes, when you haven't gotten your recommended 7 to 9 hours of sleep at night, you wake up more sluggish and irritated than you otherwise would. Your body can actually feel heavy and your brain just doesn't work as well as it could. The worst, of course, when a coworker or a friend or your mom says something like, Wow, you look tired. Ugh. But here's the thing, most of us don't actually notice how crucial being rested is until we're deprived of it. And even then, we're probably still undervaluing how inadequate rest really affects us personally, especially our brains. Did you know that even simply the process of getting ready for bed -- turning off the lights, setting the phone aside, crawling into the sheets -- even that alone changes our brains. We begin the process of slowing down.

What's going on in the brain, in layman's terms, is essentially our brain is getting a chance to not be consciously engaged in task switching all day long, and our cognitive function is going to improve as a result. And you'll you'll feel better the next day because our brain cells are having a chance to rest and regenerate and replenish.

That's Professor Victoria Garfield talking about how critical rest is to our overall health. But again, you kind of already knew that. The question is, is a good night's sleep the only meaningful way of resting your brain? How else might you give your brain a break?

We found a very clear effect of habitual daytime napping, so having a regular daytime nap, on the total size of the brain, so what we call total brain volume, as captured with a brain scan.

I have never been a napper. I'm going to get that out of the way right now. I can probably count on one hand the number of times I have actually napped. But I got to tell you, I felt pretty darn good every time I did. It was almost like I was cheating a little. And the idea that napping could actually change the size of my brain like the professor just said, well, that was pretty amazing. A little secret siesta doing all that. Again, I get it. I do. Life is busy and it's easy to think of naps as optional. And when I was thinking about this episode of the podcast, I was thinking we were going to focus on all the amazing things happening in your brain. This fire show of activity when you cycle through the stages of sleep. But the thing is this, after the conversation you're about to hear, you may rethink the idea of working through lunch. I know that I have definitely already recalibrated my own attitude about napping. So on today's episode, we're going to explore naps and the rested brain. I'm Dr. Sanjay Gupta, CNN's chief medical correspondent. And this is Chasing Life. Victoria Garfield is a senior research fellow at the Medical Research Council Unit for Lifelong Health and Aging and a professor at University College London.

One of my primary interests for the last ten years has been around understanding why we need to sleep properly, why sleep is so important for the brain and the body, especially as we get older.

How would you define a well-rested brain?

The things that we always say to people are, you know, the standard things like you, you want to be sleeping for 7 to 9 hours a night on average. That's half the battle won. And that really comes from the American Academy of Sleep Medicine. And they've been saying this for a long time now. The other thing is quality of sleep. So it might be that you you don't sleep for quite, say, 7 to 8 hours. You sleep for, say, six and a half. But the quality of sleep you're getting is good. So that is good. And that will help your your brain replenish. And then the other thing to think about that we that a lot of us don't do that helps your brain cells kind of recoup is to go to bed and go to sleep and wake up at the same time seven days a week, which again is difficult. A lot of us don't do it because there's, you know, fun things to be doing out there in society.

I have to say that you're quite right that people may often bemoan the idea of finding 7 hours at least to sleep every night. And look, I was one of those people as well, wrongly, as it turns out, believing that I could get by on far less. I'm a busy guy. I have three teenagers. I have jobs, you know all that, and I get it done now, you know, and and I mean, look, just- and I say this as a TV guy, but turning off the TV, you know, not watching TV in bed, all those things that sort of suck up your time that seem like they're giving you more benefit than just going to sleep. It doesn't pan out now. I'm telling you, as a guy in his early fifties. So it's it's really important. And I think I think people are starting to more fundamentally understand that. But, you know, Professor, my- trying to understand when you are actually well-rested, like what are the hallmarks of that, right? For me, I find that I'm I can focus better. I'm less likely to become snappy, you know, or short in terms of conversations. The other way that I was describing it recently to a friend of mine who's also a psychologist, was that every day we we have these challenges in our life, and on some days they feel like those challenges are going to crush us. We're just going to be crushed by it. And on other days it feels like, hey, it's a good workout. I don't know. That's just me. But aside from the things that we can do to get good sleep, how do you know, for example, when you are well rested just in your, you know, just your life? How do you know?

Very, very similar to the stuff you've just described for me. I'm probably not as as busy as you because I'm not on the telly, but I'm quite busy, you know, with family stuff and work and students and, you know, being a researcher, you've got to do lots of different things. Your brain has to engage in this task switching constantly when you when you're an academic. You know, just today, for example, I had to look through someone's thesis and comment and then prepare for this interview and also get some exercise and also call my mum. So, you know, your brain is is constantly, you know, switching between all these different things. And when we finish later, I have to finish writing a publication. So it for me, I think you're absolutely right that you just know when you're not sleeping well, you know. Firstly my friends are very honest and will say to me, You look really tired today, or this week. You look really tired.

Always love hearing that, right?

Yeah. Exactly. And you know, they'll say, you look really tired. Are you okay? And while that might be offensive to some people, I don't take offense to it because I know that maybe I've had a bad week and I've not slept as well. And people can tell. I think that there are there are lots of things that that, you know, show. And for me I can be quite snappy if I've not rested well. And it's great when we realize, okay, we can't, we should be doing as much as we can. But for people who maybe still can't, life is just a bit too difficult at the moment or they're too busy. It's important to remember there are lots of other things that interact with that as well. So, you know, other lifestyle modifications that, you know, if you're not sleeping as well, but you're having a really healthy lunch every day or you're able to fit in a bit of exercise that will still, still really, really benefit your brain, it's not going to make up for years of bad sleep, but it will still help.

Do you track your sleep in any way? Do you wear devices or anything to give you an idea?

I haven't done it other than when I took part in a study back in November for some colleagues, and I wore an ActiGraph, a wrist worn ActiGraph, and I had to keep a- keep a sleep diary. And I'll- I will confess, and I'm quite honest, I wasn't very good at the sleep diary. I did it. I completed it. But I in the morning I got, right, so what did I-? Oh, God. And then it really made me think, oh, God, the quality of some of this data is quite problematic, to be honest. And I did feed that back to them as well, you know, as somebody who's obviously in the field. So now I don't I don't track my sleep. I do go to sleep, go to bed I should say at the same time, roughly every week night, I don't do that at the weekend. So I roughly know how many hours I sleep. And like I say, I know when I've when I've not had a good night's sleep. And I think probably my mum is the one who gets the worst of it because she phones me and and then she said, Oh, you haven't slept well, you've got something going on you're, you're, you're a bit snappy and in one of your moods, she says to me.

You got to love moms and you appreciate the candor. Right? With all things considered.

Absolutely.

I have to tell you that I do track my sleep, you know, and I'm sort of a data guy, and I just do it off my watch. So, you know, what is interesting to me is I did find some insights, for example, even a very small amount of alcohol, like a little bit of wine or something that really throws off my sleep. And, you know, and I thought, okay, well, this is just a tiny amount with dinner, not a big deal. The insights are interesting. I think, you know, for people to do, I don't know, as you say, how good the data is to look at large populations. But for an individual, I did find it helpful. And I also found it motivating to to to not do things that were interfering with my sleep and to emphasize things that improve my sleep.

Hmm. Yeah, I agree with you. And it's a difficult one, I think, again, because with all of this stuff, we want to get the balance right. So if you're if you're somebody who is quite, you know, you're quite into data and I am for my work, I don't do that kind of stuff in my personal life. Probably just cause I'm a bit too lazy if I'm honest, to, to look at how I'm sleeping and what have you. But maybe after this, I'll I'll start doing it. I think that one thing that I think is really important to think about, though, for people is that that balance between not obsessing and creating anxiety and that again, absolutely, we know alcohol has, you know, negative effects on the brain and the body. We've shown quite recently, some colleagues have shown, that any amount of alcohol is not good for you. We all know this. However, a lot of us still consume alcohol. And here in the UK there's a very, very big culture of pubs and alcohol consumption. So again, I think it's an individual thing, Sanjay. I think that, you know, if you can take that data and make those small changes and and it's not going to make you anxious or obsessive, fine. But if we're then going to be causing ourselves other problems or, you know, mental health issues, then I think people need to be careful with those things.

Yeah, I think that's a really good point. And I try not to be obsessive about it. Everybody's going to be their own sort of, take it in their own way. But I do find it somewhat helpful for me, just in the same way that I might track my activity and things like that. Sometimes there's insights. You know, professor, I think one of the issues it seems with sleep is that people see it as sort of not necessarily wasted time, but time when nothing is happening. Right? And I could use that time for something else. How do you describe to a lay audience just the benefit of sleep? I mean, what is happening in our brains when we sleep?

Well, I mean, firstly, we know from decades of epidemiological evidence and now some experimental evidence and some causal studies that not sleeping sufficiently so or sleeping for too long and not getting good quality sleep is associated really strongly with increased risk of nasty things like diabetes, high blood pressure, having a heart attack, dementia, getting a sleep apnea diagnosis, you know, lots and lots of things that- anxiety, depression. It's a- it's quite a long list of things. So I think that those things should be enough to put people off, you know, and really think that, you know, they need to consider their sleep properly and think about it a bit more. When we go to sleep, our brains are not completely switched off, of course, that never happens and we know that we dream. Some of us remember our dreams and others don't. I don't really know what the hell I'm dreaming about, to be honest. But what's going on in the brain, in layman's terms, is essentially our brain is getting a chance to not be consciously engaged in those tasks that I was talking about earlier and task switching all day long. And our cognitive function is going to prove as a result and you'll you'll feel better the next day because our brain cells are having a chance to rest and regenerate and replenish. We know this from MRI studies and lots of lab lab work over the decades that it is important to just give your brain that rest. It's it's it's a fallacy that sleeping for 4 hours and then, you know, getting up earlier and being a person who starts work at 3, 4, 5 a.m. when you don't need to or you're not paid for it, that's not going to make you more productive and it's not going to make you, you know, be in a good mood and feel nice and be nice to your coworkers and your parents and your family members and friends. It's not going to work. You mentioned earlier TVs in bedrooms. I don't have a TV in my bedroom. Never have done. But again, it's another form of rest. Even if you just go to bed and you're just not doing anything before you sleep, it your brain is just is benefiting from all of that and the rest of your body as well, of course.

Poor sleep leading to diabetes, leading to hypertension, heart disease. What's the connection there?

So this is a very difficult question. There's two two parts. One, the epidemiological data where we do large scale observational studies, they show that, for example people who don't sleep sufficiently or sleep for too long, in what we call a U-shaped relationship, are more likely to have a diagnosis of high blood pressure, hypertension, diabetes or have a cardiovascular episode. So a heart attack, for example. Now, where it's a bit difficult is that we don't know whether these things are causal. That's one part of the issue that we don't actually know what all the pathways are, because if you think about let's go with, say, sleep duration, amount of hours you sleep per night and type two diabetes, which is a very common link that's been found for a long time, we know that people who sleep for too little, so that's normally under six or 7 hours, they are more likely to have a diagnosis of diabetes when you follow them up for, say, ten, 15 years. But what we don't know is if it's this lack of sleep per se or there's something else on the causal pathway, which we would call a mediating factor, which is in fact sleep is linked to that and that is what's causing the diabetes. Because, of course it's a very good question, because these outcomes that you've mentioned, they are vascular in nature and they are due to vascular damage in the brain and physiologically. But what we do know is that reverse- if you reverse it slightly, people who have diabetes and hypertension, for example, they have vascular damage to their brain. So we're we're doing a lot to disentangle the direction of these effects. The other problem is having multiple of these conditions and also whether they're causal and whether sleep itself, the lack of sleep itself is causing the problem or something else on that pathway. And we the truth is that we don't really know. We don't really know. It could be a number of different things, but these methods that that we're using now are somewhat easier than, as you can imagine, designing a randomized controlled trial to look at all of these things. It's a very, very complex question with a very complicated answer.

I want you to take a second to process what Professor Garfield just said there. I think this is a point worth highlighting. These types of studies are really challenging to do. You know, when you have outcomes that are rare, those are much easier studies to conduct because the cause and effect are much clearer. Poor sleep is connected to conditions like diabetes and hypertension, but scientists aren't sure if it causes those things. In part, that's because sleep is universal. People may get more or less of it, but everyone sleeps, which makes controlling for all the other factors Professor Garfield just discussed very, very hard. But I think having said all that, no matter what, it's still clear that sleep and rest more generally is really important for us and it can make us healthier. When we come back, though, a little catnap; what about that? Could it do your brain good?

What we did find that was really striking is that quite strongly habitual daytime napping seem to be linked to total brain volume.

We'll be right back. We're back with Chasing Life and Professor Victoria Garfield, who, by the way, coauthored a study on napping that was published just this past June. And when I read it, it reminded me of some reporting that I had done on stress a while back. What I basically learned was that not all stress is bad. In fact, some stress is necessary. I mean, it's what fires you up to meet a deadline to get out of bed to study for an exam, right? What is harmful, though, is when it becomes constant and relentless. Stress floods your body with the hormone cortisol. Again, you need some of this, but it also puts your body in fight or flight mode. It's good if you're trying to make a deadline or being chased by a saber tooth tiger, but constantly living in that high alert state, well, that wreaks havoc on the body. It's the constant, relentless nature of it. So sleep can be one of the only times we really get the chance to disconnect and de-stress. And that alone is hugely beneficial to our bodies and our brains. Also, it's a bit of a double whammy because when you don't get a good night's sleep, you even have higher cortisol levels the next day. So getting your Z's is another way to keep the cortisol levels in balance. And even though I thrive on stress, I need that stress to do the sort of work that I do, I realize now more than ever, there has to be this balance. There has to be these breaks. You can get those breaks in all sorts of different ways. But again, coming back to rest, coming back to sleep. It's one of the most reliable ways to actually break the cycle of stress. And napping can also be a way to give our brain a sort of reset. This is what Professor Garfield's study helped confirm scientifically.

So this idea came from essentially- there's there's a bunch of experimental American studies. And what they what they looked at was essentially whether people who napped versus didn't nap had any cognitive benefits. And these studies showed using quite a nice experimental design that it looked like people who took a nap that was fairly long actually did have better cognitive function. So their thinking skills improved, whether that be things like how quickly you process things, your memory, you know, those sorts of thinking skills that we need all day long essentially. And reaction time is very important one as well that we use, you know, when we're driving, when we're making decisions. So we took our study a step further because we wanted to look at whether daytime napping would have any effect on essentially some of these important markers that you get once you segment the brain after having undergone an MRI scan. Because some of these are hallmarks of of dementia. So the biggest takeaway is that we found a very clear effect of habitual daytime napping, so having a regular daytime nap on the total size of the brain, so what we call total brain volume as captured with a brain scan. The the effect size that we found was about 15 cubic centimeters, which again, for people's understanding, people ask, well, what does that mean? We we calculated that with previous studies to equate to about 3 to 6 and a half years of aging. So quite a big thing in terms of the age of the brain. And we think that's really important because a lower total brain volume is linked to certain diseases, earlier mortality and higher stress levels.

I want to highlight that particular point again. The study found that people who had regular naps saw an objective difference in brain size compared to those who didn't. And we don't know what that change in brain size really means. But there is an objective difference in the brain between those people who nap and those who don't. This is also important because we know that as we age, our brains shrink and that can be associated with cognitive decline. So what Garfield is saying is that the study found that regular nappers had a difference in brain volume that was equal to about 3 to 6 and a half years of aging. And what she's fundamentally saying is that people who napped regularly in many ways had younger brains than those who didn't.

I think from the research that we've been doing and I've been doing that for ten years, duration of sleep at night and quality of sleep at night, my opinion is that it can't be replaced or you can't make up for it with a nap in the day. And that's partly because also, you know, you feel that sleep pressure, you feel that pressure to sleep at night because that's when we're culturally and societally supposed to be sleeping and when everybody else is asleep. So that's when you, you know, you begin to feel tired. If you have a standard sort of day of 8 to 5, nine to six, whatever you're doing, then come the evening, once you've eaten and you've done all your evening activities that most of us do, you do feel that sleep pressure and that's due to the chemicals in the brain telling you it's now getting to that time. It's dark outside and everybody else is going to be thinking about sleeping. So I don't believe that a daytime nap can make up for it. It can help.

Is there a right length of a nap? And and is it is it possible to sleep or nap too much?

The previous studies, a lot of them have looked at cognitive function, so your thinking skills. And some of them have recommended that to get the benefits you want to be sleeping for 1 to 2 hours, having a nap for 1 to 2 hours. Now I think that's a bit problematic because we need to think about what samples those studies were looking at, for example, and if they were, say, in university students or a particular population, which might not be wholly general- generalizable to the population, we need to be careful about that. But I would say one of the issues that that people say often if you sleep for too long in the day is you wake up feeling groggy, you wake up feeling worse, and that's because you've gone into deep sleep. You're you're prepared, your brain is preparing, you know, and mimicking that sleep at night and thinks you're now ready to sleep for the rest of the day. So in order to avoid that, we've been quite conservative and said, well, maybe something up to about 30 minutes. If you if it takes you 20 to fall asleep, maybe go, you know, maybe maybe 40, but not too long. Because I think, you know, anecdotally and observationally, I don't think it's probably beneficial to sleep for 2 hours in a day.

I'm getting quite granular here because I'm fascinated by this, professor, and I'm probably going to incorporate some of this into my life. But along those same lines, is there an optimal time of day then to nap?

Very, very good question again. There's some evidence to suggest that the post-lunch period again for people we're talking, you know, vaguely a 9 to 5 type day, your average person, of course there are people working or all sorts of hours. There's evidence that the post-lunch period to take a nap is a good time to do it. So it could be that, for example, you know, because people have said, oh, what if my employer doesn't allow it or I can't do it if you have an hour for lunch, which again, thinking about resting, most of us should do, not all of us do. But if you have half an hour where you're having a nap or 20 minutes and then you eat and then you're kind of you have a few minutes and you're ready, ready to go again.

Curious, are are you a napper? I mean, did you begin napping as a result of your own your own research?

So very, very ironically, I'm not a napper. I've been asked this many times now, and it doesn't sound great, I suppose. But I in in the, you know, business of being honest, I am more likely to probably do some exercise than nap, or go for a walk. But it may be something that as I get older I think about a bit more.

Yeah. When you when you get to be like my age, you know, and much older in your early fifties perhaps. You know I have to tell you my my mom is an extraordinary person. She's in her early eighties now and I've been talking to her a lot more about things like this and just aging in general. A comment she made to me, professor, was that a change of activity can be a form of rest. And now she now she's not a psychologist, not a brain scientist, like like you or or me. But I thought that was such an interesting thing. And you sort of alluded to this a couple of times. I've noticed the word that you use is rest, not necessarily just sleep. And you even just said, you know, you might go for a walk instead of taking a nap. And I think it really does raise this question about rest and its relationship to brain health and how you define rest specifically. I mean, are there other things that we can do that maybe even seemingly are counterintuitive things to do to rest our brains?

Absolutely. Yeah, absolutely. Your mum has a very, very good point. I will always choose to take a break and have a rest, as in rest my brain, that doesn't mean literally lying down or going to sleep, by doing something which is completely unrelated to my work activities. Something that you know doesn't- that gives my brain that rest and my brain is not engaged in the same way. Of course, our subconscious is always working in the background and telling us you need to do that, you need to do this. But it's quite cool because you could have a eureka moment for a piece of research that we're doing, or you might come up with something that you want to do on your podcast, someone you want to speak to. I do things like housework, cleaning. I phone my mum and we talk about, you know, gossip. What's going on with the family in Uruguay? I might phone my partner. He's a chef, so he, you know, might phone him on my lunch break and just always have his day's going. And we talk about something else that's not work. Again, I might also put on a a 20 minute TV show, which is relaxing when I'm having my lunch on is not a documentary about brains or data or epidemiology. So I think- people here in the UK do a lot of gardening. I don't know if you know that. Very popular to do lots and lots of gardening. So, absolutely, it's a very individual thing and we can only recommend to the population, you know, what we see in the evidence. So we know that napping seems to be beneficial for the brain. But if there are other things that make you feel good and give you that rest, by all means, you know, clean the kitchen or cook a meal or call your mum or do you know, do some plants or, you know, go go into the woods or go for a run. Whatever works for you that I think is about doing a different activity, something that you're removing yourself from, from whatever you were doing before.

Well, I'll have to phone my mom and tell her that Professor Garfield agrees with her. One final question here, and this may be a short answer, but we talk a lot about sleep hygiene at night to get ready to go to sleep. Keep a cool, dark room, turn off devices, do all those sorts of things. Sleep hygiene for a nap. Is it is it the same? I mean, or do you think of it differently?

I would say probably quite similar. You want to find somewhere, you know, as quiet as you can to take your nap. Take a break from your phone, your iPad, whatever you, you know, emails, that's the big one, I think for everybody. Emails all the time, WhatsApp messages, those sorts of things. So yeah, I think quite similar. I think it can where it can be tricky, I suppose, is that if your- people have asked me this, if we're wanting to persuade employers to have a space for people to nap, how would we go about that? And of course that's difficult in the middle of a city busy office. But we do have, for example, where I work at UCL, we have prayer rooms for people, we have rooms for breastfeeding. So I think something similar where people can also nap and leave your devices behind and try to take that rest.

That was Victoria Garfield, a senior research fellow at the Medical Research Council Unit for Lifelong Health and Aging and a professor at University College London. I learned a lot from her. Let's all agree there is no shame in a nap. We can start there. It's even good for your brain. It can increase the volume of your brain and decrease your risk of certain diseases. But also, as you heard, napping is not going to make up for bad sleep habits. So you still need to get your 7 to 9 hours every night. Remember what Professor Garfield and my mom said, that rest is important, yes, but that rest doesn't necessarily have to be a nap either. There are other ways of giving our brains a rest from the constant stream of information that we're interacting with. Take a walk. Go for a run. Put your work down. Close your eyes. Maybe meditate. Do something that gives your brain that well needed rest. Next week. You might say it's the opposite of the rested brain: the caffeinated brain.

I highly recommend getting off caffeine, if only to have that experience of getting back on caffeine. If you have doubts that it's a powerful psychoactive drug, they will go away.

Thanks for listening. Chasing Life is a production of CNN Audio. Our podcast is produced by Eryn Mathewson, Madeleine Thompson, David Rind, Xavier Lopez and Grace Walker, our senior producer and showrunner is Felicia Patinkin. Andrea Kane is our medical writer and Tommy Bazarian is our engineer. Dan Dzula is our technical director and the executive producer of CNN Audio is Steve Lickteig. Special thanks to Ben Tinker, Amanda Sealey, and Nadia Kunang of CNN Health.