The Food Medic - S3 EP11 - *BONUS EPISODE* - Sleep & Travel

Episode Date: December 3, 2019

Hello and a very big welcome back to The Food Medic - we are back for an extra special bonus episode on SLEEP! On the podcast today, Hazel is joined by Alan Flanagan who is currently pursuing his PhD in chrono-nutrition at the University of Surrey. They discuss how much sleep we need, what happens when we don't get enough sleep, how sleep deprivation affects our long term health and our appetite, the phenomenon of jet lag and social jet lag, and how exercise can support a restful nights' sleep. Check out @thefoodmedic on social media for more topics like this. This podcast episode is kindly sponsored by Westin Hotels & Resorts Hosted on Acast. See acast.com/privacy for more information. Learn more about your ad choices. Visit podcastchoices.com/adchoices

Hello and a very big welcome back to the Food Medic podcast. We are back for an extra special bonus episode on sleep. Today I am joined by Alan Flanagan, who was on the podcast before. Alan is currently pursuing his PhD in chrononutrition at the University of Surrey, having completed a master's in nutrition science in the same institution. Originally a lawyer by background in Dublin, Ireland, Alan combines an investigative and logical approach to nutrition together with advocacy skills to communicate the often complicated world of nutrition science and is dedicated to guiding healthcare professionals and the lay public in science-based nutrition. Alan is a very good friend of mine and always

my go-to guy when it comes to anything to do with sleep and nutrition and the relationship between them so I'm very excited to sit down with him tonight and formally pick his brain on the topic. I'm sure we're all going to go away with a few knowledge bombs from this episode so please sit back and enjoy. This podcast episode is kindly sponsored by Westin Hotels and Resorts, who are the perfect partner for today's podcast topic on sleep and travel. At Westin Hotels and Resorts, they have a single goal in mind, to help guests travel well. This means helping guests maintain their routines, eat healthy on the road, and feel fully rested and ready to accomplish their travel goals.

To achieve this, they have curated wellness programs that allow guests to eat, move and sleep well anywhere they may travel. This includes an eat well menu created with seasonal fresh ingredients, an on demand fitness gear lending program and a Westin signature heavenly bed. All of it curated just for you so you can rise explore more at weston.com a member of Marriott Bonvoy so Alan welcome back to the food medical podcast I'm delighted to be back I'm delighted to have you back. And what better man to have on to talk about sleep and travel? Yes, all things chrono, biology, circadian rhythms, sleep, jet lag in various forms. Yeah, your favorite topic. Yeah.

So I think when it comes to sleep, the first question that everyone always asks me is, how much sleep do I actually need? Is there a magic number? So I think there's a couple of important points to make within that. And the first is that there has been a lot of awareness about the importance of sleep in particular. And I think Matthew Walker's popular book, Why We Sleep Last Year, exploded sleep into the kind of popular consciousness because it was a book by an excellent academic but written in very accessible way. The difficulty was I think sometimes being very on the academic side you often lose the practical side and there was not a huge amount

of practicality in the book and everyone came came away from it thinking, that's it. I can't drink coffee, have red wine, stay up late, do anything for the rest of my life. I just need to get thee to a nunnery, to quote Hamlet. And that's really, I think, given us this view that there is a set number. There is a universal accepted definition of good sleep. And while there is a universal need for sleep, the idea that there is a homogenous human sleep pattern is a little incorrect because sleep isn't just a defined process

that happens in the same circumstances across all different cultures. It's influenced by cultural factors. It's influenced by your region. It's influenced by light exposure. It's influenced by urban versus rural environments. So I think we need to step back a little bit and kind of reinforce to people that sleep is not a global uniform, the same act in the same place at all times. And it is influenced by these factors. And so in that sense, there is definitely a requirement for the state of sleep. Is eight hours a magic number? Not necessarily, because it's going to depend, and different people will have different,

this is something I think we'll go into later, but different people will have different, what are called chronotypes. They'll have slightly different internal biological timing that's kind of unique to themselves. So they may be more evening-oriented, or they may be more morning-oriented. That will influence their sleep patterns. Generally speaking, what we do know is that the architecture of sleep and the stages of sleep that you go through, we generally associate rapid eye movement stages of sleep or

REM sleep with where we have most kind of benefits, memory consolidation and all of these processes. What we do know is that your ability to go from one REM cycle to another becomes shorter as you go through more sleep stages. And because we sleep in, say, 75 to 90 minute cycles on average, there is definitely a benefit to having five to seven sleep cycles in a row because it allows people to get into that stage. That's roughly where the eight hours comes from. But you see different patterns of sleep in different populations. And historically, there's a lot of debate over whether we've slept in a monophasic period, so one eight hour period, or whether you accumulate that eight hours in, say, a six hour sleep and a two hour nap or siesta patterns you see in cultures

closer to the equator or the idea of what's known as second sleep which is very much speculative and derived from literature from the middle ages but the idea that in the absence of artificial light you would have perhaps gone to sleep earlier in the evening after dark, had a period of sleep, then woke and carried on kind of basic human activities and then had a second period of sleep. We can't really confirm whether that happens. But I think what I want to kind of get across to listeners is this idea that sleep is only, quote, good if you get eight hours of sleep a night between 10 p.m and 7 a.m and i don't think that's

a productive way of framing sleep health for people so yes we do know that short sleep so let's say less than five and a half hours a night is potentially associated with some negative consequences but does every single person across the world need to sleep eight hours in one chunk? Probably not. And there is definitely a variance there. And I would broadly say within that variance that perhaps seven to nine is a broad enough range and it doesn't necessarily have to be obtained all in the one particular chunk. But that one chunk should be certainly it would seem kind of six six and a half seven hours at least because in that time frame you're accumulating a lot of REM sleep yeah and you

kind of briefly mentioned that short sleep over a long period of time is associated with poor health and I think anecdotally we can all kind of relate to that when you've had a couple of nights of crappy sleep, you feel pretty crappy. You're also more susceptible to getting like infections like the common cold and things like that. But over a long period of time, and we know this from shift workers, that you can have kind of poor metabolic outcomes. So things like type 2 diabetes and heart disease and things like that. And I think that shocks a lot of people because they're like, how can sleep disrupt what goes on on a physiological level in my body?

So I thought maybe you could touch on that without kind of getting too into detail. Right. So broadly speaking, sleep, it's not an act that occurs in isolation. So we have 24 hour days. Sleep fits into our 24 hour day. And it fits into it in the context of what are known as circadian rhythms. And circadian as a word basically is derived from Latin, and it means around the day. So all organisms, all biological creatures, humans included, we have these internal rhythms that in humans go a little bit longer than 24

hours. So they're about 24 and a half hours. So we use external cues in the environment, like light and meal timing and our social activity to synchronize those rhythms. And within that, our sleep-wake cycle is a really important part of that. So everything in our body is based on being kind of anticipatory in nature. And we have all processes, whether they're to do with how we regulate our blood glucose, or the circulating levels of our cholesterol and fats in our blood, to our body temperature, to our immune system, all cycle based on this daily pattern. And in the simplest terms, it's a cycle of contrasts.

So the contrast of being asleep is being awake. The contrast of while we're asleep, we obviously can't eat. So the night nocturnal period is a fasting period. While we're fasting, we obviously aren't eating. So we have a contrast between sleep and wake. We have a contrast between feeding and fasting. And we have a contrast between activity and rest. And it's during sleep and during the period of rest and inactivity that our body essentially recalibrates, we have memory consolidation, we have immune system function, we have a kind of resetting of our ability to handle carbohydrate and blood glucose that comes in through our diet the following day. So we have all of these processes that are reliant on the phase of sleep to stay regular, so to speak. So when we disconnect that process from happening, or we simply remove it from happening,

we have consequences that are negative for health. And those consequences are both acute, and they happen the next day. And they're also chronic, so they accumulate over time. And that's where we see with shift work in particular, there's two things going on. Not only is there the lack of sleep, then there's also this circadian disruption, this disconnect from their internal rhythms. So they're actually dealing with two things that are very much related, but are also kind of distinct to a degree in their long-term health implications. Yeah. And when it comes to, like you said, so we kind of have these patterns in our day and also everything that goes in and on in our body is almost reflecting that so we've got different cycles that are happening in the day

than different cycles that are happening at night and so when it comes to how we can support that nighttime cycle there's always you know conversations around what we can eat to support our health and support our sleep and often i come across articles that will you know state specific foods can help induce sleep or support sleep and really that's not the case but it's more so there's dietary patterns and there's a kind of dietary windows that can help support our sleep. So can you tease that apart a little bit more? So I think you hit the nail on the head by stating that this idea that there are isolated foods that will help with sleep,

there's really no good evidence to that effect. You have some interesting trials, but they don't really give us much. But coming back to this circadian idea and this idea that that system really relies on contrasts, there is definitely a relationship between these biological time processes and sleep. So if we think about sleep as something that occurs in the evening biological time and like I said in humans the day phase, the light phase is when we're active and it's when we feed. What we see at a population level and in some negative effects in more controlled studies is that an effect of living in modern society for

a lot of people is that they have curtailed sleep, they have an enforced waking time in the morning with an alarm, they're not hungry in the morning for multiple reasons, and they end up redistributing a lot of their energy to later in the day. they're having very large meals quite close to when their internal biology is getting ready for nighttime. And a lot of energy intake in close proximity to sleep can disrupt people's sleep because of multiple factors. One, they've eaten in close proximity to bedtime and their body is still thinking, well, I need to process this and we're in waking mode. Two, there's simply the effect of actually going to bed full and people having a difficulty with, for example, the increased heat that's generated from having a

large meal. We actually want to cool down in the evening before bed and the kind of optimal sleep temperature is like 16ish, 17 degrees. So so the up regulation of your body temperature that comes with eating is again it's the opposite contrast to what we want in the body at that phase before we go to sleep so broadly speaking if we try and redistribute more of our energy to earlier in the day to when we're actually active. That doesn't necessarily mean breakfast. We can go into the meal timing thing a bit more. But for now, just to say that actually the biggest impact on someone's sleep in a positive sense from a nutrition standpoint is simply going to be aligning their daily meal timing with their active and waking phase that's slightly earlier or if they do eat later this much

earlier and trying to be conscious of the proximity within which they're eating say their last meal of the day to actual bedtime. And in terms of a cut off time would you say like two three hours before you go into bed? I generally like two because I think it's a little more achievable for people than three. And I should say that there are nuances and caveats to that because, you know, if someone, for example, is training quite hard or is an athlete, you know, the consideration for someone in that context is slightly different, you know. So if they train in the evening and only get home after work at, you know, 9, 9.30, I still think they're better placed having a kind of lower overall calorie but protein rich type snack before bed

rather than worrying about the micromanaging of, well, it's, you know, I'm about to go to bed. But for most people in the general population, I think that two-hour rule is quite a good heuristic to go with. Yeah, absolutely. And then if we think about people, kind of thinking of myself here, who work shift patterns, on my current job, I'm not doing night shifts, but I have done lots of night shifts on my acute rotation.

And I find it really tricky to manage my dietary intake not knowing whether to just kind of become fully nocturnal and just eat breakfast lunch and dinner in the night tried that that was quite tricky because almost when you're working through the night you feel slightly nauseated and then having to force feed yourself like a dinner at 4am is a bit weird but then not eating at all you become really lethargic and then you're sitting at the nurse's station and there's a box of celebrations and then that becomes your dinner so i know a lot of nurses and doctors follow me and one of the questions i'm asked is you know what should i be eating on a night shift do i just follow you know standard

healthy eating guidelines that you would in the day or do I not eat at all? Right. And this is one thing where I think we're really lacking research. Good, good data. Yeah. So the first thing that I think just based on your experience, which is quite consistent with I think most people that have worked night shift, whether it's in a kind of medical context or the police or the fire brigade or these kind of jobs that typically require shift work at some at some stage is that and it's the difference between you know the ideal versus the practical the ideal would be that you simply don't eat during the biological night that's not practical for many reasons like you said you either get hungry or even just that we forget that there are emotional components to food and that's completely OK.

And if it's 3 a.m., you know, in A&E and you're dealing with someone with, you know, a stabbing, you know, you're not going to exactly resist that box of celebrations, nor necessarily should you. So I think it's important that there are a lot of psychosocial factors that go into eating during the night shift for night shift workers that we should be cognizant of. The one thing that we do know is that the most negative effects of eating during the biological night are on your glucose tolerance and on your lipids, on your blood fats. And the reason for that is they're inversely related. In our circadian rhythms, our ability to process blood glucose or glucose in our diet, our ability to regulate blood glucose is really enhanced in the early part of the day.

And then at night, we have elevations in, in say triglycerides or free fatty acids because we're fasted but when they're elevated and when melatonin's high our ability to have to regulate blood glucose is quite impaired so what i'm proposing is purely hypothetical i do have an application actually drafted for this and i hope i get funding for it. What no one's really looked at and what there are certain suggestions in the sports nutrition research is that you do completely digest protein overnight. So given that the negative effects of metabolism, particularly during the night, are from carbohydrate and fat digestion, I think that if people are to plan strategic snacks during their night shift,

try and make it a kind of protein-rich, lower overall calorie snack because we know protein is also filling. So you get a satiating effect from it and maybe are able to kind of attenuate some of those negative impacts on blood glucose and blood lipids that we would see if you were eating like a bagel or a muffin, you know. So having some, I don't know, Greek yogurt and some fruit or something like that.

But again, you're into this idea that someone wants cold Greek yogurt and fruit at 2 a.m. I'm not sure. So I'm always, whenever i talk about night shift work i'm always trying to be conscious of these kind of you know psychosocial factors that go into it you know and what's someone actually going to want at 2am yeah i guess so if you're starting your shift at like 8pm when you wake up having a big meal then and in the night just kind of maybe having a snack right i think having a big meal before the shift is is generally something good and try even though this is somewhat

counterintuitive because our glucose tolerance is less in the evening than it is in the early part of the day but the fact that someone's going working on a night shift i would generally try and maybe have that meal as something that's kind of like got an adequate amount of protein and kind of higher in carbohydrate and lower in fat. And just get that kind of level of energy in beforehand. Yeah. So there's lots of things to take into consideration. I think people also need to be slightly compassionate to themselves. Like, you know, you don't need to absolutely nail your diet or when it comes to this.

Like the most important thing is you get through your shift and and feel well at the end of it but if you're doing this consistently over a long period of time this is going to be your job then there are some nutritional considerations think what you said you know they're good takeaways and similarly when we are sleep deprived what does the research say in terms of how does our dietary quantity and also quality change? Yeah, so it's really interesting, some of the experiments. And I think to clarify, when we talk about sleep deprived, a lot of the research looking at the behavioral knock-on effects of sleep curtailment on energy intake, you're talking about five and a half hours sleep.

Some people would consider that a good night's sleep. And so we're not talking about getting two hours sleep. There are plenty of people who probably consider five and a half hours sleep a good night's sleep or a decent night's sleep for them. And what we see is a compensatory energy increase the next day that almost mirrors the decrease in appetite hormones. So one of the hormones that regulates our appetite is a hormone called leptin. And when we have decreases in leptin, we have very significant increases in our hunger and our food-seeking behavior, which is one reason why if people diet and they lose a lot of body mass, they lose a lot of body fat, they have low leptin levels, they have this massive increase in their

appetite. But acutely, after one night of five and a half hours sleep, you'll have around a 21% drop in leptin levels. And there's a hunger hormone in the stomach called ghrelin, which increase by 18%. So you have this hormonal storm that combines and the result the next day is around a 22% increase in energy intake. So the increase in energy intake almost matches the change in appetite hormones, which is quite interesting. But the preference is for very energy dense foods that are calorically dense and are high in fat and carbohydrate. And part of the hypothesis with that is that the brain is compensating for the fact that it has increased energy requirements. It has to sustain a longer waking period than it usually would and isn't as rested. And the brain is a hungry organ for energy. And in humans, our brain accounts for basically 30% of our resting energy requirements.

So it is the most metabolically demanding organ that we have for energy. And it is going to make you go and find that energy if you're asking it to be awake for longer and to sustain thinking and performing. So the acute effects of sleep curtailment are a preference for energy dense foods. Generally, they're foods that are high in carbohydrate and fat and an increase in total energy intake. And are those kind of stats on the changes in our hormones over one night? One night. One night.

That's mad. Yeah. So next I want to chat to you about jet lag, which I know everyone's very familiar with the term, but what I really want to talk about is what exactly is happening to us and why do we experience it? And second of all,

what can we do from a practical point of view to reduce the likelihood of being affected when we are traveling across time zones? So earlier we talked about circadian rhythms. In humans and most organisms, the most powerful impact on our internal rhythms, on what synchronizes us to the external environment, to the time of day, is light. And it's, in effect, it's the daily rotation of the earth and the cycles of light and darkness. And so when people see a clear day and they see that sky appears blue, that blue, that what we perceive as blue is a very specific wavelength of light. And coupled with the fact that you're outdoors, you get a huge intensity of light as well.

And this all is detected by a really special set of cells in our eyes and relayed to a very particular point in our brain that signals daytime activity and all of these processes happen from that. And then of course we sleep during the night and so when you're, let's say for argument's sake, in London and you're walking to work and you're getting your outdoor light exposure and you're having your breakfast at let's say 8.30 and all of these behaviors that you're doing are in keeping with the clock time that it is here. In effect, at the most basic level, what jet lag is, is taking yourself to another part of the world where the clock time that you're used to doing things at is now completely different to the timing of the light and dark cycle and the timing of your meals. So because you've completely altered when you're doing these behaviors, your body detects that.

You arrive in a part of the world. Let's say you fly to Hong Kong from London and you're now eight hours ahead in terms of the clock time. So your breakfast that was happening at, say, 8am is now in your body. It's still 8am, but it's 2pm clock time in Hong Kong. And you're trying to sleep and you're trying to eat and you're trying to do your general behaviours at a time that is completely disconnected from where you were. And in effect, that's what jet lag is. It's a disconnect between the timing of your rhythms and your behaviors relative to where you were in the world. And there's only a very time rate limited amount that your internal rhythms can catch up, which is why, depending on how far you

go, also depending on where you travel, whether it's east or west, you have varying degrees to which you can kind of catch up with jet lag. So the reason going east is harder is because you're going into time zones. Whereas, for example, if we were going to go from London and you were going to fly to Chicago, if you left London at 11am, you'd land in Chicago at 2pm. The effect is basically the same as just staying up a bit later. So by the time you get to that evening, if you kind of force yourself to use caffeine, for example, and stay awake till the evening, you're actually very tired. It's the same as you've stayed up till 4am London time. So you may not have a great sleep, but you'll still sleep and you'll be up at a time the next day where you get outdoor light exposure and all this stuff. So you get over jet lag easier going

west. Going east tends to be different because you've gone into these time zones. In terms of how to travel to try and kind of get over jet lag quicker, there is some cool research in this area. I don't know why we don't talk about it more. And basically, it comes back to this idea of your light exposure and things like your meal timing and things like when your body gets ready for sleep. So if you're traveling east, for example, you can start to think about changing your light exposure kind of three or four days in advance of traveling. And you could start to even try and start to delay your meal timing somewhat to try and shift it to something that's more consistent with the clock time that you're going to. The other thing, and I say this with the caveat that it's generally not available in the UK, but this research group used very low

doses of melatonin at a time. So let's say that you're going to, again, Hong Kong, and let's say it's 10pm in Hong Kong is roughly going to be your bedtime. So say one o'clock in the afternoon in London, you would take that very low dose of melatonin at 1pm here. And the reason they used a very low dose is it's not enough for you to get drowsy, but it's enough that your internal, because you've taken melatonin, your internal rhythms have somewhat of a shift. The other thing that you would try and do then is consider your light environment and trying to use, kind of you can get now quite widely available blue lights and let's say in Hong Kong

it would be light in the early part of the day so you would use 30 minutes of blue light exposure at say 10 30 or 11 p.m here to actually get you that exposure that gets your body thinking we're we're changing it's it's bright even though you know it's 11.30 p.m. here, you're starting to think about actually what time is it going to be in Hong Kong when I'm doing these things. All of this is quite demanding schedule-wise. People really need to plan it. I've used these protocols before, traveling to Sydney last year,

and I advised a couple of people doing a similar trip to Australia last year that well they were athletes now but you know they put it into place and it does make a difference but you have to really be in control of your schedule to do these things and you have to have certain equipment like for example a small blue light box and yeah absolutely the other thing that is very difficult for people to do in this context is what you want to avoid doing is just randomly eating ad hoc on your plane journey because you're going to be eating at times that are inconsistent with your new time zone that is not something most people are willing to do yeah it's very difficult, isn't it? Because they're coming round and they're waking you up and giving you food,

and at that level of altitude, you're just disoriented, hungry, thirsty. You kind of eat whatever is given to you. So it does require an element of discipline, but I guess, like you said, if we're chatting about someone who's going to compete in a different country then it's in their best interest to optimize their sleep

and kind of just you know have a protocol that's on this flight but then if you're going on your holidays Right. Okay so we've talked about kind of how your sleep can be disrupted when you're flying across time zones,

but also when people are traveling within the same time zone, just going to somewhere even within the UK, for example. You're staying in a new hotel. You can feel like very disorientated in terms of your sleep's like slightly disrupted. Why does that happen? And what can you do kind of to keep your kind of routines in check? So I think this comes back to the point we said at the start

where we have this idea that sleep is just this homogenous thing, that it is constant in all circumstances at all times and that if we decided to just go to sleep right now, we would have the same sleep as if we were in our own bed. And sleep is very much a state and trait thing it is influenced by your immediate environment so so one thing that i find is i because i sleep in quite a dark environment and i make sure it's i'm really sensitive to sleeping in a hotel for example that has crappy blinds and windows and light coming through the door and i end up you

know trying to stuff extra pillows at the bottom of the door so there's and light coming through the door. And I end up, you know, trying to stuff extra pillows at the bottom of the door so there's no light coming through. So little things like that. Whereas, again, not everyone might sleep in that kind of environment. So for someone doing the opposite, if they tend to have some light coming through their window and they go to a hotel room that has blackout blinds and suddenly they're in pitch black, that would probably be off-putting to them. So it's really important that we re-emphasize that sleep is influenced by your personal preference. It's a behavioral pattern. It's influenced by what have you done in the preceding hours going up to it.

And in the very often kind of over-complicated world of sleep advice, I think actually the best thing and what makes the biggest difference for people is coming back to this idea of rhythms, building in a kind of a wind down routine that allows you to get into a state where your body is in shutdown mode and you're not buried in emails at half 10. Part of going somewhere new that may be disruptive for sleep is simply you're excited. You're on holidays and you're giddy for what you're getting up to do the next day you know so there's that element as well yeah i guess if like you said if you have a bedtime routine maybe bringing that with you so to speak so say for example a bath before you go to bed is something that you do or you have like a peppermint tea or you read

a few chapters of your book kind of having those things with you so that your body's kind of like oh that's fine yeah we know what we're doing it's time for bed yeah yeah exactly and even you know someone doesn't regularly say have a hot bath before bed even doing something like that in a new environment can help because there there is an impact of that change in body temperature that happens when you get out. Because remember earlier we said that there is a kind of an optimal temperature for sleep and it's actually cooler because our body temperature starts to dip. So people say, oh, the reason I sleep well after a hot bath is because the warmth was relaxing. It's actually not. It's because the change in the contrast in temperature when you get out and your body temperature falls, people are more induced into good sleep. So

that is something that I find. People are traveling to a new environment, a hotel, for example, actually having that, whatever they have been doing, try to carve out a 90 minutes before they're going to plan to go to bed. And at that point, starting to think about, you know, is there one of these weird little lights on in the TV? Can I, you know, can I just, I'll just plug the TV out. And then, yes, having things like a hot bath that can help induce a good sleep in this new environment.

Yeah. Something that came to my mind when we're talking about jet lag and something that you and i've spoken about before is the term social jet lag so i thought maybe we could touch on this for people who maybe haven't heard of it which is essentially happens because we have these weekday weekend cycles where you know weekday you may go to bed early and get up early but then weekends you're like later nights later starts and then you're going into your monday feeling slightly hungover from the weekend so let's chat a little bit about why that happens and is this a new phenomenon is it because we are just people who work all the time and party all the time it's new insofar as

our ability to quantify it and identify it. And a chronobiologist named Till Ronenberg at the University of Munich is one of the pioneers in this area and developed the Munich chronotype questionnaire, which if our people are interested, they can just Google it. It's freely available online. But the Munich chronotype questionnaire is the best questionnaire for assessing these things because it allows us to quantify social jet lag. Social jet lag is definitely not new simply because the industrial revolution happened and that's where we get the nine to five workday, which is basically a factory workday, but our ability to quantify it is new. So what social jet lag is, is recall that everyone has a slightly different internal timing. Your chronotype, your timing type,

so to speak, is your behavioral preference for doing things across the day. So broadly speaking, some people are what they call morning larks or night owls. Most people do fall into the middle. But what's really interesting is in the last 10 to 20 years, the estimates of the amount of people who are identifying as evening types has dramatically increased. And the theory is that that has to do with things like our artificial light exposure at night, our behavioral preference for evening activities,

and all this kind of stuff. Social jet lag, if I was to let you sleep and you self-select your bedtime and you don't have an enforced waking time the next day, how long would you sleep for? So usually for people that's on free days, whether that's weekends or other days, but the days they're not working. So let's say for someone that's behavioral preferences, they would go to bed at 11 and they would wake up at eight. Their midpoint of sleep is the midpoint of that. So let's say their midpoint of sleep is about three to 4am. And again, factoring in that all of these beneficial things tend to happen later in our sleep cycles.

But let's say now during the week, their commute dictates that they have to get up at six. So their midpoint of sleep is now pushed back, but their wake time is basically cutting half of what their kind of later phase of sleep would be like. So we can calculate social jet lag by looking at the difference and by calculating the difference in someone's midpoint of sleep when they're allowed sleep with no enforced waking versus their midpoint of sleep when they have to force themselves to get up. And the reason the wake time is something I'm focusing on is because chronotype is generally a reflection of a behavioral preference. Evening types don't tend to compensate by the fact that they have to get up earlier by going to bed earlier because they're just not tired. They're not ready for bed.

So they go to bed at the same time. What changes then is the fact that they're curtailing their sleep by having an alarm clock kick them out of bed at six in the morning. And this group in Munich and others started looking at social jet lag and the relationship between social jet lag or the extent of someone's social jet lag and their metabolic health. We had a really nice paper recently that looked at the relationship between type 2 diabetes and chronotype and chronotype evening types independently associated with diabetes and that was in effect because we talked about the effect of sleep curtailment on blood glucose levels this was independent of sleep duration so the the argument now that i think is building is that our work and school and our social timing, broadly speaking,

is all putting people that fall into this evening type at a bit of a disadvantage in terms of their health. They're the ones that are prone to develop high levels of social jet lag. They're the ones who may try and compensate for sleep on the weekends. There's one interesting study that showed that evening chronotypes had better diet quality and meal patterning on the weekends because perhaps arguably they were more well-rested and they were eating in sync with their own internal kind of rhythms. But what we see with people with high levels of social jet lag

and evening chronotypes is because they're not hungry in the morning, they skip breakfast, they have low energy intakes during the day, and they have the bulk of their energy intake coming then in the evening at a point in their biological time when they're close to sleep. So that's one of the reasons why there may be this relationship between high BMI and social jet lag, diabetes and social jet lag. But it's something for us to pay attention to. And I think we're starting to accumulate a level of research about these factors.

That means I think we have to start as a society having some kind of conversations about, you know, how do we structure our workday? You know, are we and some companies are doing this now. Some of the kind of cool Gen Z companies are allowing people self-select working hours, are taking these considerations into account. I think the most interesting and probably under-talked about element of this is in relation to adolescence and cognitive performance. So we know that during your adolescent years, independent of biological sex, both boys and girls have a phase shift, a delay in their internal rhythms. So people always say, oh, lazy teenagers sleep until 11 o'clock. Actually, they need to sleep.

And they tend to have a preference for staying up later and sleeping later. We've been tearing kids out of bed at 6am to go to school for, you know, the last 100 years or so. A couple of schools as part of a study did an experiment where they delayed the school start time till 10am. And the difference in cognitive performance was night and day. I think we need to start really having some conversations, wider conversations, I guess, as a society about how we structure our time, factoring in this emerging research about chronotype, about social jet lag. Certainly, if kids' brains are going to work better by just having the school start time shift, you know, we need to think about these things and not be dogmatic about the timing that we have set in society

simply because it's the way we've done things since the steam engine was invented. Good point. And finally, before we wrap this up, I want to chat to you about the relationship between exercise and sleep because obviously if you exercise too close to sleep, you're not chat to you about the relationship between exercise and sleep because obviously if you exercise too close to sleep, you're not going to have the best night's sleep because your heart rate's going to be elevated, you're going to be pumped full of adrenaline

but then regular, moderate physical activity can support good sleep. So what's the relationship there and what can we do? What do we need to kind of bear in mind if we try not to disrupt our sleep when it comes to exercise so i think the exercise thing is still not quite clear-cut as well i think generally speaking

the advice is well don't do strenuous exercise before bed because you'll jack up your nervous system and you'll be wired. That may be true in some people, but not in others. And there was a really nice study that looked at different degrees of exercise intensity. And the group with the strenuous exertion group had better sleep simply because, you know, walk-ups must come down, kind of. And so, yes, they had a strenuous activity bout in the early evening, but they had a quicker time to sleep, your sleep onset,

and they had better kind of subjectively rated deep kind of sleep. So I think there's a lot of individual variance in this idea of the impact that exercise has. The other thing we have to remember is, again, in terms of our circadian rhythms, you know, the day phase is our activity phase. You certainly don't have to necessarily exercise in the morning, but good levels of cardiorespiratory fitness

generally tend to correlate with good sleep. But in terms of that spectrum of intensity, should you avoid exercising in the evening because it may interfere with sleep i think that's something that people just have to maybe just experiment with themselves and if they if they do i think we should always be encouraging exercise over no exercise yeah absolutely and just find out for for yourself yeah i think like you said some exercise is better than no exercise but we also have the practical implications of if you're training at like 7 p.m at night getting home at 9 p.m having your dinner at 10 p.m is that going

to disrupt your sleep cycle and i know anecdotally i've recently flipped my training schedule for someone who used to train at 6 p.m due to work schedules i can no longer do that now train at 6 a.m which means waking up at 5 a.m and i sleep so much better now right so much better but i always thought that that i would be the opposite because i feel almost stronger in the evenings right you you'll have an adaptive there's definitely our circadian rhythms and body But I always thought that I would be the opposite because I feel almost stronger in the evenings. Right. You'll have an adaptive. There's definitely our circadian rhythms and body temperature tend to peak between, say, 4 and 7 p.m.

So there is a physiological reason why power output is greater in the evening. There's a reason why world records are broken in the evening. The 100-meter final is not on at 9 a.m. It's on at 7 p.m. But unless you're Usain Bolt, these differences are really, we're talking minor percentages, right? So for your average recreational athlete, micromanaging this is not important.

You will have an adaptive response to when you train. So if you start training at 6 a.m., it may suck for a couple of mornings, but then you'll be fine. And very much this comes down to what's your schedule like? Yeah. Well, you've dropped a couple of,

not a couple, a lot of knowledge bombs for people to take away. Any final words? I think caution against orthosomnia and yes sleep is important but there is like diet and like all health things right now i think we're starting to package them with a label of do consider these things, but don't run off the side of a cliff with doing them to all the nth degree in the extreme

because that is counterproductive. And if people start obsessing over every little aspect of getting good sleep, the exact opposite will happen. Broadly speaking, when I'm asked to give kind of the Cliff notes version, I would say, particularly this time of year, try and get some outdoor light exposure earlier in the day. Try and get 30 minutes outdoor. Even if it's overcast, the intensity of light is sufficient, even if it means popping outside for half an hour during your lunch break.

Try and think about your light exposure in the evening. Try not to sit six inches from your screen or from a 60-inch plasma. Try not to take your phone to bed because, again, that type of light is going to be quite disruptive to your melatonin levels. Try and have in the evening your kind of general domestic environment softly lit. Do think about adding in exercise. Try and think about what your natural behavioral pattern preferences are for. If you are a later chronotype, then do think about, you know, how you manage to get good sleep in that isn't cutting yourself off by having to get up too early.

Even if it's bringing your sleep timing forward by an hour. And broadly speaking, I think do the kind of basics consistently, but don't freak out. I think that's a nice note to finish on. Thank you so much for coming in today. Thank you for having me. A special thank you to the Westin Hotels and Resorts for sponsoring this podcast episode and for promoting ways in which we can maintain our healthy routines while on the road.

Thank you again to Westin Hotels and Resorts.