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Morning Larks and Night Owls: the Biology of Chronotypes [transcript]

Written by Christopher Kelly

Jan. 27, 2019


Tommy:    Hello. Welcome to the Nourish Balance Thrive Podcast. My name is Tommy Wood. Today, I am rejoined by Dr. Greg Potter. Hi, Greg.

Greg:    Hi, Tommy. It’s great to be back.

Tommy:    It’s great to have you back in what will hopefully become a tradition of hours as we do more and more podcasts together. I would like an update on baked goods in your life. Last time we talked about biscuits on the request of Dan Pardi. I think we summarized that gluten was very important for the structure of biscuits especially if you go dip it in tea which we like to do as Brits.

    Right now, we’re in the run up to Christmas. I’d like your thoughts on the various dried fruit-based baked and steamed goods, Christmas pudding, Christmas cake, all those good things that you have in the UK that are very hard to get here in the US.

Greg:    Well, they tend to polarize people, don’t they?  

Tommy:    Absolutely.

Greg:    It’s one of those subjects where people either love them or they hate them and I firmly fall into the former category. I have a lot of time for mince pies, any type of mince pie, really cheap ones, posh ones. They’re all good.

    I look forward to Christmas pudding. It’s only me and my sister that eat it at Christmas time. Everybody else is too stuffed or just not interested which is great. It means more for us. But other baked goods, if we’re focusing on biscuits, then it’s the time of year where Germany really comes into its own.  

Tommy:    Oh, yeah. Stollen. Can’t discount a stollen.

Greg:    Yeah. Well, I was thinking more on the lines of lebkuchen and pfeffernüsses. Have you had those before?

Tommy:    I’ve had the lebkuchen but never a pfeffernüsse so I don’t think.

Greg:    They rock.

Tommy:    Can you describe it to us?

Greg:    It’s basically a giant ginger cookie with a single layer of chocolate on one side of it. It’s a little bit cinnamon-y, it’s a little bit spicy, and it’s really quite lovely.

Tommy:    Sounds awesome and perfect for this time of year. It maybe after Christmas when this comes out, but I think it will still be perfectly acceptable for people to have a nice spiced baked good if that’s something that they are interested in. Okay. Enough of that.

    One of the reasons why I’ve asked you to come back on the podcast is because we have been discussing chronotypes on the podcast recently. Satchin Panda talked about how they probably don’t exist. Bill Lagakos talked about how they probably don’t exist. Every time this happens, you pop up and say something very sensible and very well-informed about why chronotypes may exist and why they may be important so I wanted you to talk about that.

    Now, of course, there’s probably going to be a lot of technical detail here. I think you’ve warned me that you may wander off into the weeds and people may wonder what on earth it is you’re talking about. But we will eventually draw it back to something that makes sense. But why don’t you just start by giving us a little bit of historical background, some of the details and context that might be important for the discussion as we talk about maybe what even chronotypes are and then go from there.

Greg:    Okay. I’m not sure that I would say that my thoughts are sensible or well-informed. But with that out of the way, I will just say that I think that chronotypes do exist. I think they exist in other animals too. I’m not sure that for people listening, they need a deep understanding of chronotype. I don’t think that knowing their chronotype will have much bearing on how they behave if they want to be healthy.

    But I do think that for people that are in positions of power and society could affect change in areas such as the workplace understanding chronotype can help them make people healthy and more productive.

    With that said, I suppose it makes sense to begin with definition of chronotype. The idea has been around since 1900 or so is a guy called Michael O’Shea. He first introduced the idea of morningness and eveningness which is really diurnal preference. It's when people prefer to engage in certain activities as oppose to some sort of objective measure with biological timing.

    But then as time has changed, chronobiology evolved and some luminaries in the field became more and more interested in the concept. There’s a guy called Colin Pittendrigh and Serge Daan who in the ‘70s came up with a more precise biological definition.

    What they were interested in is the fact that it’s probably driven by the circadian system. If that’s the case, then there should be a difference in what’s called the phase angle of entrainment to the light-dark cycle between morning types and evening types. We’ll come back for that later so just park that thought for the time being.

    Anyway, people were interested in this with respect to health outcomes and it’s difficult to measure biological timing accurately, so people then starts coming up with questionnaires. James Horne and Olov Östberg in 1976 came up with the morningness-eveningness questionnaire which categorizes people according to whether they like doing things in the morning or evening. It’s basically 19 questions that give a score of up to 86.

    You can then take people and tally up their scores. If they have a score of 16 to 30, then they’re definitely evening types according to this. If they have a score of 70 to 86, they’re definitely morning types. Some of the questions relate to the time you’ve rest the activity cycles. What time would you get up if you’re free to plan your day for example?


    Some relate to subjective perception. At approximately what time of day do you usually feel your best? The problem is that the questionnaire is just for everybody and something that will come to you later is our biological timing changes over time. What happens is people often hit the ceiling, score 86 especially in the elderly as people’s sleep-wake rhythm starts to advance and people start going to bed earlier and waking up earlier.

    Anyway, there are also less widely used questionnaires too. So Carlla Smith has one called the Composite Scale of Morningness which basically combines the MEQ with parts of the questionnaire that was created by Torbjörn Akerstedt. And then Till Roenneberg, Anna Wirz-Justice, and Martha Merrow in 2003 created something called the Munich ChronoType Questionnaire. They use separate questions for sleep-wake timing on work days and free days.

    They had an issue with the MEQ and it relies on the subjective measures, and they wanted to see if they could use a questionnaire to get more objective measure the biological timing. They focus on sleep timing adjusted for sleep dep. They also include questions related to things like light exposure which is very interesting if you have a big data set because you can then start to understand associations between some of those exposures in people’s sleep-wake patterns.

    Finally, in some very large scale studies, people just use very simple questions to try and determine if people are more morning types or evening types. In the UK, Biobank for instance, they use a very crude question which is just, are you definitely a morning type, a moderate morning type, a moderate evening type or definitely an evening type? Something that’s worth noting is that even though these questionnaires are generally, relatively rudimentary, they do tend to correlate with objective measures of biological timing.

Tommy:    When you say something like objective measures of biological timing, what are we talking about in terms of what we’re measuring and the physiological outcomes of that?

Greg:    In those instances, we’re generally talking about things such as rest activity patterns which can be determined via actimetry. So you give people Fitbit typed devices called Actiwatches which are more accurate than the consumer devices that are available and you look at their sleep-wake timing and then you compare those results to the results of the questionnaires and you see whether they agree with each other.

    Alternatively, you can use more objective measures. The main one that’s used in research is the melatonin rhythm of different people. But you can use things such as core temperature too or cortisol rhythms. The problem is that those are more noisy because they’re more susceptible to change as a result of things like physical activity. Whereas melatonin is less perturbable by change in diets and movements and so on.

Tommy:    When we’re talking about chronotypes, a lot of the discussion comes around, especially in my mind, to what happens to humans in the wild, if you want to call it that versus what happens to humans in the modern environment. Say the difference between David Samson’s work on the sentinel hypothesis in pre-industrial people versus say, Wright’s camping studies where you take people into the wilderness and see what happens when they’re not exposed to those modern dark-light cycles or modern light exposures.

    Can you talk a little about those two different approaches and sets of data and how that maybe could set us up to think about whether chronotypes are really something that’s important to think about or not?

Greg:    One thing that I was going to begin with, Tommy, is just the circadian system in general but we can come back if you’d like me to --

Tommy:    You can start with the circadian system in general and then we can come back to those studies.

Greg:    Yeah. People who are listening, who are familiar with this might want to just skip forward about eight minutes. But I do think that it’s actually very important to lay this out first because it basically tees up the rest of the conversation nicely and also, I’ll be using certain terminology in order to grasp the subsequent concepts. You need to actually understand some of those fundamental points.

    If you listen to the previous podcast that we did together, then some of these concepts would be familiar to you already. But if not, I’ll try and keep this as tight as possible, but it is important to raise certain details because I just think that when people discuss chronotype, there are certain misconceptions that regularly come up and some of that just comes down to the fact that people haven’t fully fleshed out their opinions about this particular subject.

    The circadian system is basically the result of the fact that organisms evolved in the presence of relatively predictable changes in the environment. The most important for us today is the light-dark cycle. These occur across different time scales. The daily light-dark cycle occurs as a result of the planet’s rotation about its axis each day.


    In response to that, organisms evolve their own timekeeping mechanisms, so they have predictable changes in their biology and hence, behavior across different timescales. When we speak about circadian rhythms, we’re speaking about 20 to 30-hour changes in our biology. One example of which would be the body temperature rhythm. So your body temperature varies between about 36.2 degrees and 37 degrees each day. I’m speaking about Celsius obviously.

    Anyway, the purpose of these rhythms is to both anticipate and adapt to the environment. As an example of anticipation, before you wake up each day, adrenal cortex synthesize cortisol to basically increase arousal, mobilize energy reserves, raise blood pressure, then also our circadian rhythms help us adapt to environment. There are changes in the environment that take place each 24 hours and not all of our cells are directly exposed to the external environment.

    So your liver cell isn’t exposed to sunlight. As a result, we need our own endogenous time keys, if you like. The melatonin rhythm is perhaps one of the more important ones of these so pineal melatonin synthesis occurs during darkness and signals the biological night time throughout the body.

    Anyway, biological rhythms have certain core characteristics. I'm going to ignore two of them, but I'm just going to mentioned one of them which is entrainment. This is very important to discussions of chronotype. Circadian rhythms aren’t precisely 24 hours. If you go and live in a cave for a period of days, what you’d find is that the period of your own internal clock, so the time lapse from one point in the cycle to the next point in the cycle would be about 24 hours and 15 minutes on average.

    About 25% of people with intact vision have less than 24 hours but that’s what it is on average. Anyway, because of that, the circadian system needs to be reset 24 hours each day. This occurs by way of time cues or zeitgebers is what we call them. It’s a German word.

    Anyway, the most important is the pattern of light exposure each day.  But the most important for some of our organs is probably diet. These circadian rhythms have three parameters. Tommy, sorry. I know this is ridiculously long, but just bear with me.

Tommy:    This is great.  

Greg:    One of them is period or tau. I’m going to skip amplitude because it’s not so relevant to our discussion today. Period or tau is associated with morningness and eveningness. This have been shown both at a physiological level. If you look at somebody’s internal day length in a cave for example, then they tend to be a later chronotype, and they tend to have a longer melatonin rhythm, but it’s also been shown at a molecular level.

    If you take one of their cells and you leave that in a dish and you watch the molecular clock in the cell tick away, then evening types will have longer periods of that molecular clock work.

    Anyway, the purpose of this molecular clock is basically to set a daily program that processes in each of our tissues optimizing them for specific activities with certain times of day. It’s interesting when you think about it. Everyone, the billions of cells in your body, has its own timekeeping mechanism which is driven by its own internal molecular clockwork.

    The purpose of it generally is to basically separate the timing of incompatible processes, so building new structures and breaking the damaged ones. You don’t need to worry too much about the mechanism, but it’s basically a negative feedback loop that involves gene expression and the translation of mRNAs that are produced during that gene expression.

    Anyway, this same molecular clock is present in all of your cells in your body and outside of the master clock in the brain. The timing of it is mostly set by food intake. If you look at the liver for example, you take one group of mice and you feed them 6:00 a.m. to 6:00 p.m., another group from 6:00 p.m. to 6:00 a.m. then within a few days, the timing of gene expression and clocks such as the liver is completely out of phase. So 12 hours different between the two groups. The timing of the master clock in the brain barely budges.

    Now, speaking of timing, this brings us to a phase which is another very important biological rhythm characteristic. This is just basically the timing of your biological clock right now. If you look at morning types and evening types, many studies have shown that typically there’s about a two-hour difference between circadian phase of these people. At a given time of day, the timing of the biological clock in an evening type will be about two hours earlier than a morning type.


    Now, in discussions of chronotypes, something that comes up is a concept called phase angle of entrainment which is basically the relationship between the timing of the biological clock or your melatonin rhythm if you like, and the timing of an external time key, so that might be dusk for example.

    A common one that might be used is looking at the relationship or the timing difference between when your body starts producing a significant amount of melatonin which is called dim light melatonin onset and dusk. Dim light melatonin onset just to flesh this out is basically the interpolated time of melatonin concentration continuously rises above a certain threshold.

    If your melatonin rhythm reaches 100% ultimately, then to determine when dim light melatonin onset occurs, it might look at the point at which it crosses 25% of the absolute amount. Anyway, under uniform light conditions in something like a lab, there’s a difference in this phase angle of entrainment, the light-dark cycle between morning and evening types, that’s been shown very clearly by people like Jeanne Duffy.

    Problem is that in the lab, you impose quite weak zeitgebers. The light that you are exposed to isn’t nearly as intense as the light you’d be exposed to outside. The timing of sleep relative to the timing of your body’s internal clock which is primarily a measure of phase angle entrainment to the unique light dark cycle of the lab will differ from the timing relationship that you’d see outside. So circadian phase might be later in the lab because the light-dark cycle isn’t as strong as it is outside.

    Anyway, in many studies, these phase angle entrainments were measured using the time between circadian phase and sleep timing but this is a bit of a problem because it basically assumes the timing of somebody’s sleep-wake cycle corresponds to the timing of the light-dark cycle. Sometimes, this is the case but it’s not always the case. Now, this particular topic brings us to something that’s very important and that’s basically how your master clock sets the timing of your body and responds to the light-dark cycle.

    You probably know that you have specialized cells in your eyes called rods which are important to see in darkness and then also cones which are important to color vision. Light also has what are called non-image forming functions. One of these is the circadian system entrainment.

    This was shown in early 2000s by David Berson but also Samer Hattar at the same time. They discovered these specialized cells which are called intrinsically photosensitive retinal ganglion cells which exist in the inner retina of the eye, and they contain this specialized photo pigment called melanopsin. This has the peak absorbance of light at blue wavelengths. These cells that are involved in synchronizing your body with the external environment are most responsive to blue light for this reason.

    Now, in response to light, signals from these cells fire much more slowly than from rods and cones. Basically, what this means is that they keep track of your exposure to light over time and they then send this information about light exposure down the optic nerves directly to the master clock which sits above where the optic nerves of the eyes cross and it samples this information to basically update the running record of your light exposure history.  

    Now, this master clock is the most important structure in the timing of your circadian system. There were some really nice experiments and perhaps done in the 1970s basically showed that if you destroy the SCN, then you stop all circadian rhythms and things like local motor activity, certain hormones and also feeding behavior.

    Anyway, this master clock then sends information throughout your body about time of day by things like neural projections, certain secretions that’s also involved in a regulation of body temperature and something that we’ll focus on today is melatonin.

    The master clock has this multisynaptic pathway back to the pineal gland where melatonin is synthesized during darkness, melatonin’s then distributed in the blood to other tissues where it acts on two receptors and the melatonin rhythm therefore shows the timing of the master clock, and it’s important to sleep-wake timing.

    Now, an important concept when it comes to chronotype is something that’s called a Phase Response Curve. This is tricky but I’ll do my best with it. How your body responds to light depends on when you’re exposed to it relative to the timing of your body’s internal time. If you increase your exposure to bright blue light early in your biological day, then you’ll advance the time of your master clock, so you shift your biological time earlier.


    This advance zone is about 12 to 16 hours before that dim light melatonin onset or DLMO which I mentioned earlier. Now, if you increased your exposure to bright blue light late in the biological day, then you will delay your master clock. This delay zone is typically from about four hours before DLMO or about four hours after DLMO.

    Now, if somebody is entrained or synchronized with the 24-hour world around them, as most of us are most of the time, then this phase angle of entrainment which I mentioned earlier which some people think it was an accurate measure of chronotype basically depends on first, how much your period or your tau differs from 24 hours.

    The longer you are in internal period, the greater the amount of time that you need to spend in that phase advanced portion of the phase response curve in order to maintain interim. It also depends on the strength of the relevant zeitgebers, so if you’re exposed to a lot of bright blue light outside during the day time, then you find it much easier to synchronize your clock with the external environment.

    And then the other thing is how responsive you are as an individual to changes in the light-dark cycle. I know, Tommy, one of the things that you wanted to come to you later is the fact that if you look at adolescents for example, then they are more responsive to the phase delaying effects of late light exposure on the circadian system.

    It’s plausible that differences between chronotypes could be explained by differences in sensitivity of evening types, for example to the phase delaying effects of evening light exposure or they could be less sensitive to phase advancing effects of morning lights and the converse would be true in morning types.

    The final thing I mentioned on this discussion might be the longest answer in Nourish Balance Thrive history is that sleep homeostasis might also influence chronotype.

    There’s been some work showing that it’s possible that some people’s chronotype could be more dependent on how the circadian system responds to change in the light-dark cycle whereas other people’s chronotype might depend more on sleep homeostasis.

    That circadian regulation I mentioned earlier in one subset of morning types and evening types so those with very extreme phases, so very late types or very early types. It might be that evening types have very strong responses to those phase delaying effects of late light exposure and the morning types would have the converse responses.

    But then if we consider sleep homeostasis, then in another subset of chronotypes, so those with intermediate phase in particular, it could be that the differences are consistent with differences in sleep homeostasis which is basically the pressure to sleep that accumulates with more time awake.

    The idea is that as your brain is active during the day time, every second of the waking day, you’ve got chemicals that are accumulating in your brain that promote sleep. During this neural activity, presynaptic KTP is released into the extracellular space. This can then be converted to adenosine, or it can activate the signaling of sleep-regulating cytokines like TNF-alpha and IL-1 beta.

    Anyway, adenosine, it inhibits some wake active neurons in certain parts of the brain and it disinhibits and stimulates the sleep active neurons, so it makes you drowsy. And then likewise TNF-alpha and IL-1 beta, they stimulate sleep active neurons in an area at the hypothalamus and some other brain regions that are important for generating slow waves which are integral to deep sleep.

    It could be that morning types have a higher rate of decay of this slow wave activity which basically means that when they go to sleep, they pay off their sleep pressure faster, and that helps them wake up earlier. That could be the longest response ever. I can go into the sentinel hypothesis now if you like me to, Tommy.  

Tommy:    The important thing becomes how we start to integrate this into what people might want to do for themselves or figure out about themselves. The sentinel hypothesis is basically some evidence for different chronotypes in pre-industrial populations or hunter-gatherer populations.

    And then maybe you can contrast that with the work that I mentioned where if you take people who are morning types and evening types, so you take them camping where they just get exposed to the natural light-dark cycles than those who are who say they are late types or evening types, they then start to look more like the early type. How do we separate some of those stuff out?

Greg:    Sure. The sentinel hypothesis has been around for a while, but I’ll focus on some work that a guy called David Samson did, and he’s at the University of Toronto. It’s published last year.


    The basic idea is that during sleep, we’re uniquely vulnerable. For that reason, you might’ve expected actually that’d be strong evolutionary pressure against the selection of sleep-like behavior. But anyway, the principle behind the sentinel hypothesis is that to reduce the risks of sleeping, animals that live in groups should share the task of vigilance during sleep. So you want some individuals to stay up and make sure that the pack is safe.

    David Samson went out and he studied the Hadza people of Tanzania in East Africa. What they did was they took people and they gave them those Actiwatches that I mentioned earlier. Using actimetry, it basically showed that over 20 days of observation, everybody was scored as being asleep at the same time for a total of 18 minutes.

    During 99.8% of the time, the people were asleep, any one person was asleep. There was at least one person awake. Basically, there’s always somebody awake. What David did was he looked at the midpoint in the time between sleep onset and awakening as a marker of chronotype. He found that the variation in the activity levels of people, so when somebody was awake, is related to variation and chronotype. That’s a stable trait.

    You had some people who consistently went to bed late, some people who consistently went to bed early. As a result of this, there was always somebody up. This variation in chronotype in his data set was only driven by age.

    He basically used the statistical technique where he also looked at things like sex, the number of children that were sleeping in a family, whether somebody was nursing and also the study day corrected for the weather but none of those things influenced chronotype. It was only age. He had some really interesting hypothesis about why this might be the case. This is slightly tangential but I’m just going to mention it because it is very interesting.

    One of the things that he mentioned was that it could be the people with rare chronotypes in a population would be favored if they are awake when most others are asleep. The quiet times can represent opportunities for attacks and being awake would obviously reduce mortality risk.

    Alternatively, there could be some group selection like five groups of people that show more variation in chronotype because that would help protect them. Another aside which is very interesting is that if you look at mammalian species, those that experience the greater risk of predation of sleep sites tend to have less REM sleep which is that stage of sleep in which you dream. Your body is paralyzed during it.

    Humans have shorter sleep than any other primate. They also have a higher proportion of REM sleep than any other primate. That probably relates to the fact that we don’t really have many predators. In this pre-industrial population, you’ve always got somebody up more or less. It’s a stable trait from one person to the next, and it’s driven by age.

    Now, if we then contrast that with camping, then the most relevant studies were done by a guy called Ken Wright at the University of Colorado. He’s published two great papers. If you’re very interested in this subject, then I would really recommend that you read them because it’s just terrific science. One of them is 2013 paper.

    Basically, what they did was they took healthy adults and have them go camping in the middle of the summer in the Rocky Mountains for a week without any exposure to artificial light, whatsoever. What you found is that people’s biological clocks tightly synchronized with the natural light-dark cycle, such that the beginning of the biological night time when melatonin synthesis increases sharply occur roughly at sunset and at the end of the biological night time, that coincided with pretty much wake time which was just after sunrise.

    What he found is that people who are only exposed the natural light didn’t have nearly as much variation in their circadian timing as they did before the experiment. If you look at the timing of people and their sleep-wake cycles prior to the experiment, then those with the latest timing had the biggest shifts in their own biological timing during the experiment. The later chronotypes have larger circadian advances when they were only exposed to natural light.

    They then did a follow-up experiment four years later. In this instance, there are people who go camping during the winter. They went camping for six days, and what they found was that melatonin onset, so the start of the biological night time within six days shifted by two and a half hours earlier after camping which is pretty remarkable.


    Average sleep start time also shifted by about two and a half hours. Melatonin offset did much the same and some of the wake times too. Basically, what happened is that the start of the biological night occurred earlier. The start of the sleep episode began earlier. But then the end of the sleep and the end of the biological night time occurred roughly the same time as before. As a result, sleep duration increased by about two hours and 20 minutes in total for a night.

    What was interesting is that sleep duration, if you plotted sleep duration across the six days of the study actually continued to increase. That suggests that that wasn’t just the the fact that people hadn’t been getting enough sleep before the start of the experiment. Because if that was the case, then the first night that they would have slept the longest and then a little bit less the next night and so on.

    Anyway, they compared the results to the 2013 camping study. What they found is that before the start of the camping intervention, if you look at the timing of people’s biological clocks when they were back at home, so in the electrically lit environment, their melatonin rhythms were similar during the winter and the summer.

    But if you then compare what happens post-camping then during winter, the melatonin onset tends to be earlier and melatonin offset was a little bit later than the summer. The melatonin duration was about four hours longer in the winter than it was in the summer within just six days of camping.

    So that suggests that our bodies have the ability to track the seasons and changes in day length. And then something that will get you later is the concept of social jetlag. They did a sub-study in this particular study where it basically had five people spend the weekend at home and then nine other people go camping just for the weekend.

    In this instance, they did have some exposure to artificial light while camping but only flashlights and headlamps. They found that during that weekend exposure to natural light, they achieved 69% of the shift in circadian timing that is reported in the previous mid-summer study.

    Just a single weekend with camping achieved more than two-thirds of the shift in biological timing of an entire week of camping. If you compare that to David Samson’s sentinel study, then what we see is that people in the modern environment tend to drift later, their biological timing delays and it’s probably a result of weak time cues which is something that we can come back to primarily less light exposure during the day time and perhaps more light exposure during the night.

    Just to give you some stats on that, we now probably spend about 88% of our tim indoors in the electronically lit environment. If you look at nocturnal light pollution, then between 2012 and 2016, the extent to which it spread over the world but also the increase in intensity rose by about 2.2% per year. This is becoming increasingly problematic.

    We’re basically spending more time indoors now and we’re also exposed to more artificial light at night. Both of which mean that we’ve got weaker time cues and because on average, our clocks are longer than 24 hours, our sleep timing is delaying. If we can recapitulate natural environment such as those that you see in pre-industrial people, then our body’s clocks have the ability to readjust very quickly to those circumstances.

Tommy:    There’s a couple of things that strike me that come out of all of that. The first one, and maybe we should start with this, is that if much of the differences in chronotype are driven by age, then when you think about something like Wright’s studies, most of the people I believe were of a very similar age, so then you would expect most of them to come together to a very similar rhythm once they’re exposed to the same light-dark cues.

    But then equally, this means that the inherent underlying genetics of what our period or tau may be means a lot less than our age does. Is that right?

Greg:    Possibly. Something that you need to bear in mind with Ken Wright studies is that they are studies of a small number of people. We do know for sure that when you look at very large groups of people in agreement with David Samson’s work, age seems to be the strongest determinant of biological timing.

    If you look at women for example, on average the latest at about 19 1/2 years of age. Men, they keep delaying a little bit longer because we go through puberty a bit later. So men reach their latest at about the age of 21 and therefore men are on average, slightly later than women for most of their lives. And then by the time we reach about 50 years of age, the difference between sexes is pretty much nonexistent anymore.


    With that said, circadian system genetics definitely do influence biological timing. If you look at everybody of a given age, then you will see variation and timing and you might think about that’s just the reflection of the fact that some people are exposed the very strong time cues and other people aren’t exposed to very strong time cues.

    But if you look at sleep timing across somebody’s life span, then somebody’s sleep timing relative to their peers of the same age is quite stable. If you, right now, are a night owl compared to your friends, then that would probably be the case in 20 years’ time too.

    To go now to circadian system genetics, then we know that twin studies have shown that morningness or eveningness is moderately to highly heritable. Maybe 40% to 70% of the variants in people’s timing is attributable to genetic variance.

    There are very rare circadian system variance which will have very pronounced effects on people’s biological clocks. Maybe the first study that showed this clearly was a paper that was published by a guy called Kong Toh from the University of Utah in 2001. He studied something called familial advanced sleep phase syndrome which is basically this heritable advance in sleep timing. Everybody in the family goes to bed very early and wakes up very early.

    They identified this autosomal dominant which basically means that if you get the abnormal gene from one of your parents, you’d probably get the disease. They identified this autosomal dominant circadian gene variant and it led to a four-hour advance in sleep temperature and melatonin timing.


    This particular variant was a mutation in a gene called casein kinase 1 epsilon. You don’t need to worry too much about that. It was a mutation in the casein kinase 1 epsilon binding region of the period two gene, and that’s a clock gene.

    Basically, what might be happening is that the molecular clock in people’s cells as a result of this mutation is turning over faster. As a result, the internal period of each of their cells is shorter. And then because they got this fast clocks, they have this very early chronotype.

    Other genes have been shown to have similar effects too. More recently, Michael Young who actually was a Nobel Laureate in Physiology or Medicine last year, did some work last year showing the mutation, another one, a clock gene. So cryptochrome 1 results in familial delayed sleep phase disorder.

    These people that go to bed very late and then also wake up very late. But interestingly, more people carry this particular genetic variant. It might be as much as not 0.6% of the population.

    Then finally, there have also been genome-wide association studies and they’ve tried to work out if there are certain gene variants that are involved in the sleep timing in hundreds of thousands of people.

    A few of those have shown that genetic loci near established components of the molecular clock such as period 2, period 3 and another gene called FBXL3 are associated with morningness and eveningness. So we’ve got this variation between ages, but also within your peers of your age, you do see variation and it probably is related to circadian system variance.

    I know, I was joking with you, Tommy, before we spoke about the fact that I’ve always been an extremely early chronotype. I was just a strange child. Whereas most kids, they say to their parents, “Mom, Dad, I want to stay up later.” By about 6:00 p.m. in the evening, I’d say, “All right, time out. I’m done for the day. I want to go to bed.” I’ve always been that way.

    I think that if you had a very big camping experiment like those that can Ken Wright did with people of a given age group, then after everybody had stably entrained to the new light-dark cycle and people have paid off their sleep debts and so on, then you would still see some variation between biological timing, between people.

    It wouldn’t be nearly as great as what you see before the start of the experiment when people are living in the modern, electronically less environment but you definitely would still see morning types and evening types. In my mind, those people at either end of the bell curve are the true morning types and evening types.


    The problem at the moment is that we have these studies that say, well, this person reports being definitely a morning type or definitely an evening type. But really much of that could just be a reflection of the fact that they’re spending all their time sat inside. And weak time cues during the day and then at night, they’re on their iPad watching another episode of Game of Thrones shortly before sleep.

Tommy:    Then I guess the question’s become about what then is relevant to the greatest number of people because obviously, these familial inherited genetic polymorphisms that cause big shifts in circadian timing, they’re interesting to help us understand the system, but that’s probably not relevant to most of us like you said.

    When you do, as far as I know, nobody’s done a big enough study where say, you have hundreds or thousands of people at the same age because in a pre-industrial population, you study a group of people. There aren’t that many people in the same age bracket just because those group of people aren’t nearly as big as you would have say in an industrial city or be close to that. So then how do we figure out what becomes most important for most people at what time in their life?

Greg:    I think the important things for different people are actually going to be consistent across their lives. I do think that there are certain populations because of the natural change in chronotype across age that needs to be targeted specifically. An obvious example of this would be school start times in adolescents and there’s been some really nice work in recent years. There was a study by the RAND Corporation last year which basically reported that they did this mathematical modeling analysis.

    The result of that suggest that if school start times in the US were delayed to 8:30 a.m. in the morning in 47 of the US States, then on average, the US economy in years to come would save about $9.3 billion per year. Academic achievement would improve. There’d be fewer traffic accidents and you just see these beneficial effects across the board.

    Definitely, there are certain people that should be targeted. But I do think that fundamentally, the behaviors that we need for our circadian systems to function well are much the same between people. There are probably exceptions.

    If you have people who, for example, have dysfunctional photoreceptors in their eyes, they can have something called non-24-hour sleep-wake rhythm disorder where basically, their biological clocks run free and they need something such as melatonin supplementation to synchronize them with the 24-hour day because they can’t do so by way of their eyes.

    You have those rare exceptions to it, but otherwise for the rest of us, it really comes down to us engaging the behaviors each day that we need in order to be healthy and then the same behaviors that are going to benefit all aspects of your health.

Tommy:    Going back to the teenager component, I didn’t realize that school starts so early over here in the US. My high school or secondary school, I think it started sometime between 8:45 and 9:00 a.m., something like that. I had to be up like 8:30.

    Whereas here, it’d be much earlier. It could be 7:00 a.m. because the school bus system means that different schools and kids of different ages share the same school buses so they have to stagger the start time of the school so that the school buses could do multiple rounds of picking kids up for school which is not something that we have to deal with in the UK because generally people live closer to the school and get there under their own steam.

    It’s very interesting that that kind of an organizational aspect like that can then have such a huge trigger effect on the population at large. But what I was wondering is I think you mentioned that in adolescence, we are the most sensitive to the light-dark cycle.

    Is the answer to set up the school system such that it’s better timed with the response of the adolescents to the environment or should we be focusing on the environment that then supports adolescents to then function within the system that they already exist? Does that make sense?

Greg:    Yeah, it does. I think it’s probably a bit of both. I can’t really give you a good answer to this. Of course, you can do a modeling study like that and you can try and account for everything. But we live in a complex environment by which I mean that there are sensitive dependence on initial conditions. You can’t forecast what’s going to happen.

    For that reason, you can try and consider all these different things that could influence the outcome of interest, but actually there’s no way that you can accurately do. But anyway, with that in mind, I think that the solution would be two-pronged.

    Part of it is okay. How do we try and nudge these people into engaging in the types of behaviors that are going to help with circadian system alignment and health in general? But then also the other part of it is, well, if we recognize that this is important and there are numerous examples of this in adults too that we could speak about how people have tried to adjust things like work schedules based on chronotype.


    Then if we make some of those changes in school start times and work times and so on, then we can probably counter some of the effects of this change in biological timing on negative health outcomes. Much of this comes down to the fact that if people are going to bed later, then they still have to wake up at a certain time which can be most problematic in adolescents and they’re not going to get enough sleep. Their sleep time is going to be more variable which might, in itself, be problematic.

    As a result, they are going to suffer from all of these negative consequences that late chronotype has been associated with and then also this related construct social jetlag has been associated with recently.

Tommy:    Let’s dig into that a little bit, the concept of social jetlag versus maybe something like sleep debts. I think this component of the variability in sleep timing of people with later chronotypes and how that might be associated with disease outcomes. But equally, there’s also some potential benefits or some things that later types are better at compared to morning types and vice versa. Can you parse some of that out?

Greg:    Yeah. It probably makes more sense to start with chronotype actually just because chronotype is maybe the main determinant of social jetlag. What we know is that late chronotype or eveningness, and I know I’m being slightly lax in my use of those terms because they are related but somewhat distinct.

    But anyways, it’s repeatedly been associated with both less healthy behaviors but also a greater risk of some diseases. If we think about behavior, then late chronotypes associated with things like smoking and consumption of more alcohol, more processed foods, but it’s also associated with various metabolic health impairment such as diabetes, sarcopenia in men, metabolic syndrome in women and developments of gestational diabetes during pregnancy.

    This year, Kristen Knutson published some work on the UK biobank dataset which is this incredible resource of people are interested in health. It’s freely available and there are hundreds of thousands of people and all sorts of measures on these people.

    But anyway, they looked at more than 430,000 adults. They use that very simple proxy chronotype that I mentioned earlier just a single question. What they found was that people who reported being a definite evening type compared to a definite morning type were a greater risk of psychological disorders, diabetes, neurological disorders, gastrointestinal and abdominal issues or spiritual disorders too.

    Overall, greater [0:48:04] [Indiscernible] based on chronotype, was associated with a small increase in risk of death from any cause. This is worrisome because in recent years, it seems the chronotype in the general population is progressively delayed. Again, that’s probably larger because we’re spending less time outside during the day and were exposed to more artificial light at night. Now, with all of that said, there are these rare instances in the literature where a late chronotype has been associated with better outcomes.

    Actually, using that UK Biobank dataset, there were some work published last year showing that in this group of nearly 480,000 adults, these are mostly middle-aged adults, cognitive performance which was assessed using this battery of these different tests relative to intermediate chronotype was greater in evening chronotypes. Morning chronotypes actually have the poorest performance, but that contrasts other findings.

Tommy:    Can I quickly insert to ask what time of day they assessed that cognitive performance?

Greg:    Yeah. Well, that’s a good question. I’m not sure that it was standardized but I think we’d also have to think that in a group of people that big, then any effects of that might be washed out. That could be wrong, but I’m not sure that it was standardized. If you’re doing a study of that scale, then you’re probably not too concerned about some of those specifics and you just want to get as many people through the door as possible. In young people, late chronotypes have been associated with poorer academic performance.

    Martha Merrow has done some work looking at Dutch high school kids for example, and they looked at grades in a variety of subjects over the academic year and they found that late chronotypes were a disadvantage in exams on scientific subjects specifically.

    Also, they found that when late chronotypes were examined early in a day going back to what you mentioned before, they performed worse. I am picking an individual study there. There have been quite a few studies that have looked at that type of question recently, but it does show some of these contradictory findings that we found in the literature so far.


    Now, if we then go to social jetlag, this is a term that was coined by Till Roenneberg and Marc Wittmann in 2006. Basically, the idea is that for most of us, because we sleep in on the weekends. It’s as if we’re flying a time zone or more to the east at the start of the working week because we go to bed earlier and we wake up earlier too.

    Late chronotypes predictably are an increased risk of suffering from the social jetlag. If they typically fall asleep about two hours later than early chronotypes before work days that they only have to -- well, they still have to wake up, so then you wake up maybe half an hour later, then they get less sleep and these people, they rely  on alarm.

    In that dataset, they found that about 80% of people use alarm clocks. One result of this is sleep dep. Anyway, Till Roenneberg did this enormous study in 2012, more than 65,000 people. He found that about 69% of people experience at least one hour of social jetlag.

    What he found is that beyond sleep duration alone, so I mentioned that these people are getting less sleep, the late chronotypes, beyond the effects of sleep duration alone, social jetlag’s associated with increased BMI in those adults who are overweight and obese. But also social jetlag’s been associated with various other cardio metabolic abnormalities, all sorts of different things like dysglycemia, dyslipidemia, excessive inflammation, insulin resistance, metabolic syndrome and also perhaps poorer function of the circadian system.

    Even though one hour might not sound like much, I think an important thing to recognize is that this is chronic. If people are going through evenly small disruptions on a regular basis, then those effects could accumulate over time. If you think about mechanisms, then that would be one of them but also like chronotype, social jetlag’s associated with some poorer health behaviors.

    So lower physical activity is one of them. But if you think critically, then it is plausible that some of these associations between social jetlag and metabolic problems reflect some sort of reverse causality. It could be that people who have poor health choose certain jobs which could in turn influence social jetlag.

    But again, these effects are relatively consistent. Many studies have shown this and the effects do persist once people are left statistically adjusted for various different confounders.

    So then that’s the other part of your question. Social jetlag is just one measure that we could use of variability in the sleep timing. It’s calculated using something I mentioned at the start the Munich ChronoType Questionnaire test. There is a guy called Konrad Jankowski who’s at the University of Warsaw who wrote what I thought was a very thoughtful piece last year about how depending on sleep patterns, it often makes sense to use preferred sleep timing as opposed to actual sleep timing when calculating social jetlag.

    I have not the time to revisit that paper, but I think it is open access and people can take that out if they’re interested in more. There are lots of other measures of sleep variability that we could use. Till Roenneberg who came up with the social jetlag recognizes this.

    One of his ex-PhD students, Dorothee Fischer, has written about some alternatives recently but then there are also other measures too. There’s inter-daily stability. You could use something called the Gini coefficient which was actually borrowed from economics. It’s used in economics to measure income and equality, but you can use all these different things.

    When people have started to use some of these other measures of sleep timing variability, that instability in people’s sleep-wake patterns does consistently seem to be associated with poorer health outcomes.

Tommy:    If you try and tie lots of this together, it may be that there’s both genetic and age determined susceptibility to environmental cues which may increase the risk of a delayed dim light melatonin onset or a later chronotype.

    Then as a result of various societal constructs in terms of when people are then expected to perform or go to school, you create more of a sleep debt and greater variability in timing of sleep from work days, the weekends and then either the debt of sleep itself or the variability in zeitgebers and associated sleep, that then may be the downstream effect or that may then cause the downstream effects on our health.


Greg:    Yeah. It’s a perfect storm of sorts.

Tommy:    Before we go back into how the big picture and how this affects people individually and how they can use this to better to improve their health, I have a question about seasonality and latitude. You mentioned going back to Wright studies that in the winter, regardless of sleep debt or social jetlag, there seems to be a longer sleep period, a longer melatonin period in the winter when obviously it’s darker for longer.

    Could it be part of the issues we see with our circadian timing and the general detriments of effects of the modern environment may be that there is no seasonality in our circadian rhythms anymore particularly for those people who are at higher latitudes.

    They’re further away from the equator, so then they would have much shorter -- or their genetics may expect much shorter melatonin periods during the summer when there is essentially no night time versus the winter when it’s basically dark 22 hours a day. Is that something that’s maybe a part of this?

Greg:    It could be. I don’t think that we know. I know that I don’t know. But also I just don’t think that it’s been studied thoroughly. I think it’s exceptionally difficult to study. It seems perfectly plausible to me that the way we behave should change with the seasons and that that’s going to be more relevant to certain people from some parts of the world than to other people.

    It’s clear that our body’s biological clocks can adapt to the season. If you compare the results of those Wright experiments then clearly, our bodies can adjust to the season. The melatonin rhythm was much longer during the winter, during that prolonged dark episode than it was during the summer as an example.

    There are people who tried to determine whether there are seasonal variations in certain human behaviors but also health outcomes. I haven’t looked at this work at all recently, but there used to be evidence of a seasonal pattern in human fecundity, the rate at which people were getting pregnant and I think that there was a point in time at which that was largely nullified and I’ve read some hypotheses about why that might have been a product of various industrial developments.

    And then also, there was a paper in H Communications maybe a couple of years ago. I think their lead author’s name is Dopico, D-O-P-I-C-O, and they looked at seasonal changes in gene expression. They found that during the long dark nights of the winter, people have a more inflammatory phenotype.

    To me, that makes perfect sense because actually, one of the things that I find myself is that of course I’m more susceptible to colds during the winter. But if I have for example, slightly dry skin, then that would be exacerbated during the winter. I think that it’s plausible that that kind of thing could reflect changes in inflammation.

    But anyway, the people that have considered all of this relative to chronotype and genetics have started to try and understand this more clearly and I’ve looked at some of that work recently. Basically, the idea is that light-dark cycle is quite stable in near equatorial regions.

    For example, certain African countries but they vary with latitude of course and with season. It’s plausible that when humans migrated out of Africa, we evolve adaptations in the circadian system in response to these more variable light-dark cycles.  

    There’s a guy called Dmitry Sveshnikov from Moscow. His data from the 1000 Genomes Project from five different African and 11 Eurasian populations to try and identify these genetic signatures of latitude dependent selection of genetic variants associated with chronotype in genome-wide association studies. We found that among the Eurasians, some of these gene variants actually came from Neanderthal genomes which is quite interesting.

    And then also, there’s a researcher from São Paulo in Brazil called Mario Pedrazzoli and he’s used the Morningness-Eveningness Questionnaire which I mentioned earlier and the MCTQ, the Munich ChronoType questionnaire to show that higher latitudes, people who live in higher latitudes, tend to have delayed sleep phase in Brazil within the same time zone.

    That’s a long way of saying, I don’t know but does seems to have been some genetic selection for specific variants as people migrated out of Africa. How relevant is this to human health? I’m not sure. It seems perfectly plausible that it is. Also, it will be fascinating to see if it’s possible to design studies that show that maybe we should behave differently across the seasons.


Tommy:    I’m thinking about the fact that when you say the longer nights are associated with a more inflammatory phenotype, then I feel like many people immediately go, “Well, if I just exposed myself to summer time light cycles continuously, then I won’t ever have that inflammatory phenotype but maybe, there’s some underlying expectation of that in our physiology that should happen once a year and we just don’t know the downstream effects of trying to eliminate that because we’re worried about inflammation.

Greg:    Yeah. I don’t think it’s just going to be a productive light-dark cycles either. I think temperature is going to be very important. Humidity might well factor. And then of course, people eat differently different times of year. I’m sure those changes are much more subtle than they used to be. But I think that most of us do right now, me and you Tommy are focusing on our dried fruit dense biscuits. Midsummer, that might not be the case.

Tommy:    Well, then, all those concentrated carbohydrate sources during the winter maybe also out of phase of what we expect because well, you can dry a bit of fruit and keep it to the winter but in reality, my genetics may expect much lower carbohydrate intakes during the short days because traditionally from the Nordics there’s pretty much no carbohydrates in the environment that time of year. All of that I guess, well, hopefully we can parse that out over the next few years.

Greg:    I don’t care what my genetics expect. I just like biscuits.

Tommy:    Which is also an important factor to take into account. To start to bring this back to general principles that the people can use for themselves, I’m thinking about a year or two ago, there was a very popular book by Dr. Michael Breus called The Power of When.

    He did what you’ve suggested is maybe not the right thing to do which he separate people into four different chronotypes. They were named after different animals and then you were supposed to do different things at different times of day based on what your animal type was.

    However, when I listen to you talk, it really sounds like the majority of those differences would really fall out if people did give themselves consistent zeitgebers that were again, much more similar to what we would expect in the natural outdoor environment.

    Can you give us a little bit of your thoughts on how we can then mold the environment to best produce health outcomes and whether there are any detrimental effects of timing our daily activities to the resulting outcome of the environment we expose ourselves too?

    Rather, should we be molding the environment to create a more consistent chronotype at a given age or should we be molding our behaviors to the resulting chronotype we get from the environment we expose ourselves to. Does that make sense?

Greg:    I think my answer will show whether or not it makes sense. It’s similar to what we speak about earlier that yes, you can try and set up your environment to make sure that your circadian system is functioning well and some of that will come down to the powers that be.

    But then also, what I would say is that even if there’s variation between people in their biological timing which should become less significant as people start to engage in more healthy behaviors, people can still focus on when they do things relative to their own timing. The easiest way to focus on this is just looking at when you do things relative to your own sleep-wake cycle.

    I spoke at a conference in October about Chrono-nutrition. I had some questions then about whether people should measure their melatonin rhythms for example. I just thought, it’s just not necessary. You just focus on getting enough sleep, being consistent in your sleep patterns and then thinking about in that instance when you’re eating relative to your sleep and going about things that way and then not thinking too much about things which ultimately should be relatively inconsequential.

    I think it would probably just be useful for me now to outline some of what I think are the most important things in optimizing the functions of our circadian system. Does that make sense?

Tommy:    Yes, perfect.

Greg:    If we think about our circadian systems in general in the master clock, then I suppose I should first mention that it’s worth tracking certain behaviors. If you don’t measure it, you don’t manage it right if you’re using that old aphorism. But if you think about a day time, then you’re trying to build physical activity into your day and you’re preferably doing so outdoors.

    A really simple thing that you could do is go outside for a half hour work during your lunch break, if you have a lunch break. I know that you have spoken with James Hewitt recently, Tommy. I’m sure that James shared similar sentiments about that.


    During the day time, you want to also make sure that you’re engaging in regular physical activity but not doing very strenuous physical activity too late in a day. I suggest that you stop that by at least three hours for bedtime. You want to engage in mentally challenging activities for the most part concentrate these when you feel best prepared for them.

    But if you do find them stressful, then you’re best putting them early in your day. I think for most people, they aren’t used to napping. They’re probably best served by minimizing napping especially late in a day. So maybe then seven hours or so of bedtime.

    And then if you think about the night time now, then before bed, it’s really important to try and engrain a consistent routine. One of the things that he mentioned was the environment and I took that as thinking about the environment probably from a higher level than what you were thinking.

    If I now come down to that level, then you’re trying to basically make your home a place where it’s easy to make the right decisions. I’m not an expert in behavior changes, something I’d like to find out more about, but you’re basically trying to make it easier for you to do what you need to do.

    Anyway, pre-bed, you’re going to try and engrain a consistent routine. Minimize stressful activities in two hours before bedtime and different people find different things stressful. For some people, checking email is stressful. For other people, clearing their email reduces their stress.

    Common things that people would find stressful will be things like exposure to the news in this day and age. I would suggest that you have a hot shower about an hour before bedtime because that’s going to raise the temperature of your skin. It’s going to help you lose heat from your body and that’s going to get you into deeper sleep faster. And then put your socks on because you want to keep your extremities warm because that will actually aid heat loss too.

    Something that I wrote about recently on our blog is the fact that making a to-do list is something that many people find beneficial. Michael Scullin from Baylor University published a cool paper recently.

    Basically, what they did is they had people write a to-do list for their coming days and they asked them to list as many items as possible. They found that when people did that, they fell asleep faster. Interestingly, those who listed more items had the greatest improvements in time to fall asleep because basically, you are unloading your mind of things that otherwise could be swimming around in the back of it.

    I’d suggest that you do something relaxing the 30 minutes or so before bedtime. What that is depends on you as a person. That could be reading a novel in dim lighting. It could be doing meditation for example. And then if you think about actual sleep environment, then you want to save your bedroom for sex and sleep. Obviously, you want to remove any clutter so you don’t find it stressful.

    Obviously, one of the things that we spoke today is the fact that artificial light, especially blue light can disrupt sleep and delay circadian phase. So you want to remove any unnecessary sources of that artificial light from your bedroom especially anything that omits blue light.

    If you must have an alarm clock that omits light, then you want to pick one that omits red lights. I would suggest that you dim your lights maybe two hours or so before bed. On average, the phase angle of melatonin relative to sleep timing is about two hours. So your body starts producing significantly more melatonin, about two hours before sleep. To facilitate that, dim the lights around that time.

    If you’re using digital devices late, then use a digital sunset. Use f.lux in your laptop. Use Twilight if you have an Android phone. Use night shift mode if you have an iPhone.

    In your bedroom, block out source of light from the outside world, so you can use blackout blinds or you can just use a mask. Masks are really helpful just to have handy in general. If for example you go traveling and you try and have a nap on a plane, pull out your mask and you’ll probably find that quite useful.

    You want to keep your bedroom cool. As I mentioned, you want to raise your skin temperature, you actually want a cool bedroom because that’s pulling the temperature of your body in the right direction. If you don’t have AC or anything like that, you live in a warm country, then I do suggest that you use a fan because that serves the jewel purpose of also drowning out any extraneous noises that could otherwise disrupt your sleep.

    Otherwise, you could use a white noise machine or ear plugs. If you find those comfortable, I don’t personally, but many people do find those very useful. And then what you want to try and do of course is give yourself enough time in bed.

    For some people, they have to wake up at a certain time of day. One way that they can try and give themselves more time in bed is to advance their sleep onset which means lots of light exposure early in the day, get outside as soon as possible after waking in bright daylight and be very meticulous about your pre-bed routine.


    And to engrain that pre-bed routine, a better way to use your alarm is to set an alarm for the start of your pre-bed routine instead of an alarm for the morning. Obviously, many people have to wake to alarms in the morning. If you do so, then I would suggest that you set your alarm as late as possible and avoid pressing snooze. Basically, each time you wake up to an alarm, it’s a stress to your body especially to your cardiovascular system. You want to leave that as late as possible.

    Some people, they use different apps which reportedly wake you from a certain stage of sleep and I haven’t seen any convincing data that they actually do this, but some people do find them helpful because you don’t want to wake yourself up from the deepest stage of sleep because you just have lots of sleep and you’ll feel groggy and it will take you a while to kick into gear.

    And then finally, if you wake up at night, then you want to use as little light as possible when going to the bathroom. But if you wake up at night just because your mind is raising for example, then something that I do regularly that I find really useful is I just do a body scan meditation. You can Google body scan meditations by people like Mark Williams or Sharon Salzberg.

    You don’t have to do these guided. You’ll pretty quickly learn to do it by yourself but the idea is that you just scan through your body sequentially. Many people find that relaxing. Meditation have certain effects on your autonomic nervous system which should be conducive to restorative sleep. I think that that probably is useful for me personally.

    If after a period of time let’s say half an hour you can’t fall back to sleep, then you want to associate, you want to condition yourself to associate your bedroom with sleep. It’s fine to get up, leave your bedroom for a bit, go and do something in dim lighting that you find relaxing, maybe read a book. That’s probably a good option.

    The final thing that I mentioned is diet because this is important to sleep and also it’s very important to metabolic health as Bill Lagakos very nicely laid out in a recent podcast that I very much enjoyed.

    The principles that I generally suggest people to stick by with respect to diet timing are first, to stop consuming anything other than water in the two hours or so before bedtime. Although if you have a non-caffeinated herbal tea, then that’s probably not a bad thing. Some people for example might like chamomile tea. Personally, I think that it’s a diuretic for myself, so I try and avoid it. But that’s just an example where it’s probably fine to break that rule.

    Caffeine will interfere with sleep homeostasis. I mentioned adenosine. Caffeine’s an adenosine receptor antagonist. For that reason, it blocks the interaction with its receptors and reduces the pressure for you to fall asleep. So stop consuming caffeine within about nine hours or so at bedtime.

    Actually, I would just suggest generally, that you just consume caffeine as early in a day as possible. I suggest that you stop consuming alcohol within about four hours of bedtime. Alcohol tends to let people fall asleep faster and it gets them into deep sleep faster but it fragments the later sleep. The sleep is less restorative. Alcohol does have all sorts of disruptive effects on the circadian system especially in certain organs actually such as the gut.

    Then monitor your pre-bed fluid intake. You don’t want to wake up to pee during the evening in general or just think if people stop consuming fluid after dinner, that’s probably a good starting point. And then something that Bill spoke about, I believe, is that frontloading calorie intake is generally a good thing for metabolic health.

    For many people, if they consider their total energy intake during the day and then reapportion it so they’re shifting more of it earlier in their biological day time, that’s probably going to be a good thing. But then if you do strenuous activity, then don’t be afraid to put a significant proportion of your energy intake around the bouts of activity.

    Tommy, I know that you gave a great presentation at AHS this year on The Athlete's Gut -- I think people should go and check that out if they want more details about why it’s probably not a good thing to eat immediately after a very strenuous exercise.

    Then finally, I would just say keep your meal patterns consistent throughout the week when possible. Ian Macdonald for example at the University of Nottingham has done some cool work in recent years showing that when people consume meals more regularly as in six meals a day as oppose to a varying number of three to nine meals, they tend to have better blood sugar regulation, low hunger and various other benefits to just this one example.

    Those would be, in my opinion, the most important things to making sure that your circadian system’s functioning well, you’re getting the sleep that you need because actually that’s an enormous component of this too and hopefully some people find that benefit.

Tommy:    I’m sure they will. I’m sure they’ll also have found this incredibly interesting as I did. I’m so glad that you were happy to come on and talk about it even though you say you’re not an expert. We were talking about this and I realize you probably were the expert that I wanted to talk to about it and this has been great.

    Thank you so much for your time. I am certain this is not the last time we will have you on the podcast. Greg, it’s been a huge pleasure.

Greg:    Yeah. Well, it was a pleasure, Tommy. Thanks, mate.  

Tommy:    Cheers.

[1:15:44]    End of Audio

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