You probably know your body follows a circadian rhythm, and probably think of it as primarily regulating your sleep/wake cycle, which it certainly does. But your body’s internal clock also regulates many other physical, mental, and behavioral changes that occur every 24 hours, and working with your circadian rhythm, rather than against it, can boost your health and happiness.
Here to unpack how to do so is Russell Foster, a professor of circadian neuroscience and the author of Life Time: Your Body Clock and Its Essential Roles in Good Health and Sleep. In the first part of our conversation, we discuss some science and background on circadian rhythm and its connection to light exposure. We then turn to the practical implications of having an internal clock, including whether you need to worry about viewing blue light at night, the significant mental and physical harms that can accrue from working the night shift and what can be done to mitigate them, what influences your chronotype and whether you’re a morning lark or a night owl, whether you should be concerned if you’re waking up in the middle of the night, why you wake up to pee in the night, the best times of day to exercise, and how the circadian rhythm can influence when you should take medication.
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Brett McKay: Brett McKay here, and welcome to another edition of the Art of Manliness podcast. You probably know your body follows a circadian rhythm, and probably think of it as primarily regulating your sleep-wake cycle, which it certainly does. But your body’s internal clock also regulates many other physical, mental, and behavioral changes that occur every 24 hours, and working with your circadian rhythm, rather than against it, can boost your health and happiness. Here to unpack how to do so is Russell Foster, Professor of Circadian Neuroscience and the author of Lifetime: Your Body Clock and Its Essential Roles in Good Health and Sleep. In the first part of our conversation, we discussed some science and background on circadian rhythm and its connection to light exposure. We then turned to the practical implications of having an internal clock, including whether you need to worry about viewing blue light at night, the significant mental and physical harms that can accrue from working the night shift, and what can be done to mitigate them, what influences your chronotype, and whether you’re a morning lark or night owl, whether you should be concerned if you’re waking up in the middle of the night, why you wake up to pee in the night, the best times of day to exercise, and how the circadian rhythm can influence when you should take medication. After the show’s over, check out our show notes at aom.is/circadian.
Alright, Russell Foster. Welcome to the show.
Russell Foster: I’m really delighted to join you, Brett.
Brett McKay: So you have spent your career researching circadian rhythms, our internal clock that governs our physiology and we’ll learn about today, our mood and other things as well. How did you get into this line of research?
Russell Foster: Well, I didn’t get into circadian rhythms to begin with. I went to university thinking I would become a marine biologist because I loved animals, I loved zoology, and I loved swimming. So, duh, it’s obvious. I was into marine biology. Then I discovered physiology in my second year at university and found that fascinating, and particularly how photoreceptors, light sensors work. And I became really obsessed with, first of all, the pineal photoreceptors of tadpoles. And you can record from this third eye light responses. And in fact, when you dim the lights, it would trigger a swimming response. And so I got into weird photoreceptors. Then for my PhD, I was working on the photoreceptors in birds that measure day length and that triggers their reproductive responses.
So as the day lengths increase during spring, it triggers reproduction. And I was fascinated about, well, what’s detecting that light, and how is it being measured? How do they measure the length of light versus dark? And that then got me into the circadian field proper, which is what receptors in the eye of mammals, creatures like you and I, are detecting the light-dark cycle for the regulation of internal circadian rhythms. And at that point, it was simply assumed, well, we knew it was the eye, but it was assumed that it would be the visual cells. And I know we’re going to talk about weird photoreceptors in the eye later, but really it was a passion for light-sensing systems that got me into clocks.
Brett McKay: And then along the way, you became a sleep researcher too.
Russell Foster: Well, yeah. And that was fascinating because I was working at Charing Cross Hospital at that point as part of Imperial College in London. And I was in an elevator with a psychiatrist and he said, “Oh, you work on sleep, don’t you?” And I said, “Well, yeah, kind of.” And he said, “Well, my patients with schizophrenia have terrible sleep. That’s because they don’t have a job. So they go to bed late, get up late, miss my clinic and don’t have friends.” And I thought that was one of the most stupid things I’d heard. But it triggered an interest in, well, what is going on with those individuals? So hooked up with another psychiatrist and we looked at her subjects, her patients with a diagnosis of schizophrenia. And we measured really for the first time their sleep-wake profiles. And what became really extraordinary for me is that their sleep-wake patterns were absolutely smashed. And so I sort of then moved into humans and sleep research, combining both a knowledge of circadian rhythms, these internal 24-hour body clocks, and how circadian rhythms in turn regulate our 24-hour sleep-wake cycle.
Brett McKay: Well, let’s talk about the circadian rhythm in our internal clock. So scientists have noticed for millennia that humans and other animals have a bodily schedule. We want to wake up at a certain time and go to sleep at a certain time. And for most of that time, they thought it was just light that was driving that. And it is, we’re going to talk about that, your research in photoreceptors. But then scientists discovered that we have an internal clock that ticks independently of external cues. How did scientists discover this internal clock?
Russell Foster: Well, with all good biology, it started with good observation. And back in 1729, I think it was, there was a French sort of scientist, de Mairan, and he was studying the movements of leaves of a plant called mimosa. Many of your listeners may be aware of this plant because it’s that plant where you touch the leaves, they close up. And what happens with those mimosa, it’s really worth having one of these in the house, is that you see that the plant’s leaves open during the day and they close at night. And of course, the assumption was this is driven by the changing light levels. And so what de Mairan did was put these plants in a light-tight cupboard and then sort of would peek in at different times and see what the leaves are doing. And to his astonishment, the leaves continued with this opening and closing movement under conditions of complete darkness.
And that’s one of the key criteria of identifying a circadian rhythm, something that persists with a rhythm of about 24 hours under constant conditions. Now, those early experiments by de Mairan had a potential flaw in that he controlled for light, but he hadn’t controlled for temperature. So Candolle, about 100 years later, took these mimosa plants down to a salt mine, constant darkness and critically constant temperature and observed again, these opening and closing of leaf movement. And so this was the first, and it was in plants, not in animals, where circadian rhythms were first sort of observed quantitatively rather than just sort of anecdotally.
Brett McKay: And then when did we discover this in humans? How did they discover that humans had this similar thing?
Russell Foster: Well, I suppose one of the first experiments analogous to those plant experiments was in Mammoth Cave in Kentucky where two researchers went down. And this is in 1938-39. And they showed that sleep-wake cycles would continue under conditions of constant darkness and constant temperature. But then work stopped, really, during the Second World War. But after that, a chap called Aschoff in Germany built some bunkers where you could control light and temperature exquisitely, and then started to systematically in the 1960s and ’70s, study human rhythmicity under broadly constant conditions.
Brett McKay: Okay. So we have an internal clock that keeps us to a roughly 24-hour schedule. And that clock works even if we’re cut off from external stimuli. So if you put yourself in a temperature-controlled, light-controlled room, your body will stay on a 24-hour cycle. But without external stimuli, it’s not going to match the day-night cycle. It’s going to start to drift. So for our circadian rhythm to line up with that day-night cycle, this is called entrainment, it needs external stimuli, the most important of which is light exposure. So what role does light play in our circadian rhythm?
Russell Foster: Yeah, I think it’s probably good just to step back a bit and sort of think about what our biology needs to do. And what we need to do is deliver the right stuff at the right concentration to the right tissues and organs at the right time of the day. And it’s the circadian system that gives this time structure for life. But it’s no good having a clock ticking away, fine-tuning our biology to the very demands of the rest activity in the light-dark cycle unless it’s actually entrained or locked onto that light-dark cycle. And the most powerful signal is the dawn-dusk cycle. And this is where I sort of got into circadian rhythms because I was fascinated. We knew that in the mammals the receptor was in the eye because if you have no eyes as a result of a terrible accident, then your sleep-wake cycle, you get up later and later and later each day, you’re drifting through time. So it’s by an average, let’s say, of 10 to 15 minutes each day you’re getting up later. Or if you are in complete darkness, you again show that drift. And it’s due to the eyes.
Brett McKay: But the thing that puzzled me is that how can it be that the visual cells, the rods and the cones, can also be used for circadian light detection? What I mean by that is what a visual cell has to do is grab light in a fraction of a second and forget it’s seen that light to give you a crisp image of our world. What the circadian system needs is a overall impression of the amount of light at dawn and dusk, and this could be gathering light information over minutes and sometimes hours, and I couldn’t see how visual cells could provide that time of day information. So we started working on mice with hereditary retinal disorders where the rods and the cones had broken down as a result of gene defects. So these animals were visually blind. They had their eyes, but they were visually blind. And so we decided to put them in running wheels, you know, a little running wheel in the cage and monitored when they would start their activity and end their activity under a light-dark cycle.
Russell Foster: And to our astonishment, these mice could regulate their circadian rhythms. Not only could they do it, but they did it with the same sensitivity as those mice with their rods and cones. So there was something else in the eye because if you covered the eyes up, this response to light would cease and the mice would start to drift through time. And so this then led to the hunt for what this third receptor might be and we were able to show this in mice, and Dennis Dacey was able to show this in monkeys and others were able to show it in other groups of animals, that there’s this third receptor in the eye which we’ve called photosensitive retinal ganglion cells. And what they are is that there are multiple layers within the retina, that part of the eye where the rods and cones are contained. And beneath the rods and cones, there’s the inner retina, which does some processing of the light signal.
And then they send that information to the ganglion cells and the ganglion cells have these long axons which project from the eye into the brain to form the optic nerve. And what turned out to be, and it’s still, I think it’s still extraordinary, is that there’s 1% or so, depends on the species, but certainly a small number of those ganglion cells are directly light-sensitive using a blue light-sensitive photopigment called melanopsin or OPN4. And so yeah, the eye is not only the organ of space because it provides us with our sense of vision, but it’s also, in a sense, the organ of time because it can coordinate the external light-dark cycle with the internal day and make sure that everything is synchronized so we’re doing the right thing at the right time.
Brett McKay: Okay, so the big takeaway there is there’s a third receptor, photon receptor, in our eye, not just cones and rods.
Russell Foster: Exactly.
Brett McKay: So you could be blind and still be synced up with the dawn-dusk cycle.
Russell Foster: Absolutely. And we were able to show that. So we, I was in a seminar, and an ophthalmologist was talking about his studies on an elderly lady who had no apparent rods and cones as they were able to detect. And so I said to him in the question time, “Well, what’s her sleep-wake cycle like? Does she sleep and wake normally?” And he said, “Well, I don’t know. I’m an ophthalmologist. Why would I ask something like that?” So anyway, we worked with this ophthalmologist and discovered that this lady with no conscious light perception was still able to regulate her rest activity cycles perfectly normally. It’s really quite extraordinary. And so, and we were able to work out that it was those photosensitive retinal ganglion cells. We were also able to show in that individual that these new photoreceptors do more than just regulate the clock. They seem to provide a generalized measure of environmental brightness to, for example, the pupil. Part of our pupil constriction is actually being regulated by those photosensitive retinal ganglion cells. We also asked this lady if she had any conscious detection of light. And she said absolutely none.
But Dennis Dacey had shown that these PRGCs in a monkey project to some of the visual structures in the brain. So we thought, well, maybe she’s got some subconscious ability to detect light. And anyway, we did some studies with her. And yeah, absolutely. When we turn the lights on and then off for a period and we asked her whether the light;s on or off, she could always tell when the lights were on and off, even though she had no conscious awareness of light. So really that and more studies in mice have shown that these receptors do a heck of a lot of brightness detecting tasks, including regulating levels of alertness, even heart rate in some circumstances. And indeed, it looks as though they’re contributing to mood. So increased levels of light, you can increase alertness and you can also alter mood. So yeah, it’s turned out to be something quite extraordinary.
Brett McKay: How can the timing of our light exposure influence our circadian rhythms? That is, if we got exposed to light earlier in the day, will that affect our circadian rhythm overall?
Russell Foster: Well, that’s a really key point, Brett, because morning light advances the clock. It makes us get up earlier and go to bed earlier. Dusk light delays the clock. We go to bed later and get up later. Now, that’s important because light during the middle of the day is not having too much of an effect. And we’ve shown in university students around the world that those who are owls, they have a late chronotype. They like to go to bed late and get up late. And we can talk more about chronotype later. They were missing morning light, which would advance the clock, but they were getting the late afternoon, early evening light, which would shift them to a later time. So when you see light, it can be incredibly important in influencing whether you want to get up late or go to bed early.
Brett McKay: What if you see light at both times? Like I wake up early and I’m exposed to light during my morning walk. And then sometimes I’m out at dusk and getting light exposure there. What does that just kind of balance things out?
Russell Foster: Exactly. And in fact, when we were all agricultural workers, and up until 1800, more than 90% of the population were agricultural workers getting symmetrical dawn-dusk exposure. And so we stayed beautifully on cue, rose to the sun and went to bed with dusk. And in fact, artificial light was really expensive up until the 20th century. I mean, in the 19th century, a candle, which actually isn’t very bright and wouldn’t have had much effect on the clock, was the cost of a working man’s daily wage. And so people just synchronized their biology with the dawn-dusk cycle quite naturally.
Brett McKay: So lately there’s been a lot of talk about how viewing blue light from our digital devices before bed can disrupt our circadian rhythm. So people say, well, you should avoid that, or if you’re going to use it, turn your screen yellow, you wear these orange glasses. Is there anything to that idea?
Russell Foster: No, in short. I mean, this is a rapidly moving field but what’s happened in the past few years. So the early studies looking, for example, at a Kindle, and people were asked to look at a Kindle on its brightest light setting for four hours on five consecutive nights. And that delayed sleep onset just statistically significantly by nine minutes. So a small effect there, but it did have an effect upon the rhythms of melatonin. And so this sort of got into the literature and the press as, oh, well, reading a Kindle before you go to bed is a disaster for your circadian rhythms. And of course, it had a tiny effect on sleep-wake. And then the experiments were repeated.
And instead of people being kept under dim light before the evening Kindle use, they gave them bright light, about six hours of bright light, say about 500 lux during the day. And that bright light exposure completely abolished any subtle effects of light in the evening. So we’ve got to be really careful. These are great experiments that were done, the initial ones on the Kindle, but they were lab-based experiments. They didn’t take into account the real-world situation. And if you’re getting moderate levels of light during the day, you’re not going to be sensitive to dim light or so sensitive to dim light in the evening. So that was one of the studies that has been overturned.
There’s been recent reviews looking at the use of yellow-blue blocking glasses on behavior, and there’s no effect of that. And indeed, these screens that shift from blue-enriched light to red-enriched light, the f.lux computer programs have also been shown to have no effect upon circadian biology at all. So it’s one of those things where we discovered that these photosensitive retinal ganglion cells are maximally sensitive to blue light. And people have said, ah, well, it’ll be blue light that will be important for disrupting these receptors and the circadian system in the evening. But the key thing that’s not really appreciated is that these receptors need quite a bit of light for a long period of time. And the impact of that light will depend upon how much light you’ve seen during the day, how old you are, the angle of gaze. And so it’s turning out to be a very complicated signal that’s being integrated by those receptors and then by the suprachiasmatic nuclei.
Bottom line is we don’t have any strong evidence that blue light, as sort of the levels that you get from computer screens and all the rest of it, will actually disrupt your sleep in the evening. Now, of course, if it’s brighter, it will. But remember, these receptors need bright light for a long period of time. That’s the other thing about the experiments in the lab. They’ve looked at not just a small exposure, a short duration exposure, but people have been given six or seven hours of light exposure. And you need those long effects with dim light to get any sort of a shift in the circadian system. So what the circadian system is doing is integrating light over long periods of time to get an effect.
Brett McKay: Oh, okay. So you can throw away your yellow-orange glasses.
Russell Foster: Well, I would. I mean, I just think it’s, yeah. And there’s a whole industry that’s sort of built around that sort of stuff. Yeah.
Brett McKay: What about just exposure to artificial light in the home at nighttime? Does that affect your circadian rhythm?
Russell Foster: This is a really interesting question, and we, again, we don’t fully know because the experiments have been extrapolated from lab experiments where people have been kept under relatively dim light, and then exposed to dim light in the evening. And they’ve been exposed to durations of light for six, seven hours. Whether that can map onto the real world, we don’t know. But there are estimates suggesting that, you know, about a hundred lux, which is not very much light with six and a half hours of exposure, can have a bit of an effect upon the clock. But that will vary enormously.
Some studies from Australia have shown that the sensitivity of the clock between individuals can vary hugely, and that’s independent of age. And we know that the clock is getting less sensitive as we age. So there’s lots of factors going on here. And at the moment, we don’t have the evidence base for hard recommendations about light exposure in the evenings. It makes sense not to get bright light exposure in the evening, because that will delay the clock. But how bright that light should be and for how long, and for what color or wavelength, we don’t fully appreciate it. So rule of thumb, minimize light exposure in the evenings, but you can certainly read your Kindle. You can look at your computer without worrying too much.
Brett McKay: And I think you’ve mentioned in the book, the thing you gotta worry more about with your smartphone or your devices, it’s not the light, it’s just that it stimulates your brain a lot. So it makes it harder to go to sleep.
Russell Foster: Absolutely. It’s an alerting effect. And of course, the great enemy of sleep is anxiety and stress. And yeah, looking at social media or doing emails or whatever is gonna increase your alertness, and perhaps stress levels and that will undoubtedly delay your sleep onset. So that’s the problem with social media and why I think most of us would recommend not using these smartphone devices or stuff like that before you go to bed, because it’ll increase levels of alertness. Now, of course you can use a Kindle for your relaxing book, your few pages of Jane Austen or whatever it is that relaxes you and gets you off to sleep. That’s not a worry. But it’s the sort of interactive stuff, and the stress that you get from work emails and all the rest of it.
Brett McKay: All right, that’s really interesting. We’re gonna take a quick break for a word from our sponsors.
And now back to the show. What happens when we un-sync our bodies from the usual wake during the day and asleep during the night schedule? Like what if you’re a shift worker? What goes on, what happens?
Russell Foster: Well, I think this is such an important issue, and of course there can be short-term and long-term effects of night shift work. So the sort of thing that we see with relatively short levels of disruption of sleep and circadian rhythm disruption scarred on our emotional responses. So fluctuations in mood, irritability, anxiety, loss of empathy. What’s so fascinating that a tired brain is not good at picking up the sort of social signals for other individuals, and reading what their moods and their emotions are like. High levels of frustration. I think another fascinating one is risk taking and impulsivity. We’re much more likely to do stupid and unreflective things. Yeah, I’m sure I can go through that traffic light before it goes red, or example.
Negative salience, some very interesting studies from Germany have shown that the tired brain remembers negative experiences, but forgets the positive ones. So tired people, their whole worldview is being influenced by the stuff that they remember, which is invariably negative. You’re also much more likely to use caffeine to drive you through the waking day and then try and reverse the effects of caffeine with sedatives such as alcohol or sleeping tablets, both of which do not provide a biological mimic for sleep. They sedate you, they don’t actually help you get to sleep. So that’s some of the emotional responses. Cognitive responses, so our whole ability to function, to come up with novel solutions to complex problems is impaired by lack of sleep. Our ability to multitask. So to extract from all the bits of information that we’re being bombarded with constantly, what’s relevant to what we should ignore. So multitasking falls apart. Memory consolidation, information processing, concentration, decision making, all those sorts of attributes that make us such a special productive creature are lost with a tired brain.
And then if we move on to the sort of impact on physiology and health, after years of night shift work, so we have increased levels of cardiovascular disease, altered stress responses. It seems that we override the chronic need to sleep by activating the stress axis. And what activation of the stress axis will do will be of course to increase blood pressure, you’re pumping harder, your heart is pumping harder, you’re releasing more glucose into the circulation. So that’s gonna have metabolic problems. Increasing levels of blood glucose, predisposing to Type 2 diabetes, lowered immunity. The one thing we know about high levels of the stress hormone cortisol is that it will reduce the effectiveness of the immune system, which is why you have higher rates of cancer and indeed infection in night shift workers.
And in fact, the World Health Organization has now said that night shift work is a probable carcinogen because of the higher rates of cancer you get in night shift workers. Particularly the studies that have convinced the community has been on nurses. You know, nurses doing night shift work, 15, 20 years have high rates of colorectal cancer and breast cancer and that’s controlling for smoking and all the other factors. Oh, and the the other thing I should mention, of course is really important in terms of if you are vulnerable to depression and psychosis, lack of sleep can shift you and disrupted sleep can shift you into that depressive or psychotic state. And there are even data emerging now.
We’ve known for a long time that that poor sleep in the middle years is a risk factor for dementia when you’re much older. But we’ve never had any real sense of what the mechanisms are. And with the discovery of what’s been called the glymphatic system, which is sort of a toxin clearance system within the brain. And the glymphatic system is clearing a misfolded protein called beta-amyloid. And beta-amyloid is a buildup within the brain is associated with dementia, for example. And we know that even one night of no sleep, you can actually detect in the cerebral spinal fluid a sort of a slight increase in beta-amyloid. So over years of not sleeping well, you’re gonna get a buildup in beta-amyloid, which is gonna predispose you to dementia. Now, I’m not saying that poor sleep is gonna cause dementia, but if you are vulnerable to developing dementia, that buildup of beta-amyloid is gonna nudge you in the wrong direction.
Brett McKay: Alright, so shift work sounds like it’s terrible for you.
Russell Foster: Yeah. And I, but I think we’ve gotta be realistic here. We’re not gonna put the 24/7 society back in its bottle. So what can employers do now to mitigate some of the effects on their employees? And I think this is a really important issue because it’s no good just sort of saying, you can’t do shift work. Well, we’re gonna need shift workers for, you know, frontline in hospitals, and looking after our transport systems, and all the rest of it. So a couple of points I’d make is that one of the great problems that you have as a shift worker is falling asleep after the night shift on the journey home. And there was a study from the UK showing that 57% of junior doctors had either had a crash or a near-miss driving home after the night shift. Well, why not install, you know, apps on your phone, your smartphone, which can detect your head nod or the movement of the car laterally and alert you to the fact that you might be falling asleep.
And of course, you know, high-end cars now have this technology built in. Loss of vigilance and tiredness in the workspace. Well, you could introduce bright light in workstations to increase levels of alertness, and make you less likely to fall asleep and have an accident. I think a really, really important point is that, you know, night shift workers have poor physical and mental health. So why aren’t those vulnerable individuals having a higher frequency health checks to detect these problems before they become chronic? And I think that’s in an early detection, we see obesity, Type 2 diabetes, metabolic abnormalities in night shift workers.
What’s the food that’s available? Well, it’s as bad as it could possibly be. It’s high fat, high sugar in vending machines or in the canteens. Nobody, and I think this is extraordinary as far as I’m aware, is providing our night shift workers with high protein, easy to digest snacks to get them through the night. Failure to appreciate the consequences of night shift by the employee and family. The divorce rate in some sectors can be six times higher for night shift workers compared to day shift workers. So we should be providing this information to the broader family or group that this person is living with, explaining that this person hasn’t turned into a monster, but this is a consequence of driving your biology outside of its normal range.
So there’s stuff that we can do. And you know just to finish on that, this section is that we know that these pathologies get worse with time. So should we think about limiting night shift work to three to four years on, and then maybe three to four years off? I don’t have the data to support that suggestion, but I think it’s something we should be looking at. The problem of course, is that most people don’t want to do night shift work, but they have to because of economic circumstances. So there’s a number of factors that are being integrated here. But I think we could support our night shift community far better than we are currently doing.
Brett McKay: So you mentioned earlier that there are different chronotypes. So we all follow a roughly 24-hour circadian rhythm, but some of us wanna start our day earlier or later. What causes those differences?
Russell Foster: Yeah, there’s three basic components to one’s chronotype. One is our genetics. So we’re now seeing, you know, in those key clock genes that have been discovered, subtle polymorphisms can make you more of a morning person than an evening person. So there’s a genetic element. The second is how old you are. So from about the age of 10, there’s a tendency to want to go to bed later and later and later. Women peak at around about 19 and a half, men, about 21. And men tend to have a longer more owl-like chronotype. And then from the late teens, early 20s, there’s a slow move to a more morning chronotype until you’re about, you know, your late 50s, early 60s, and you’re getting up and going to bed at about the time you got up and went to bed in your pre-puberty area.
And I throw in puberty there because of course those changes in chronotype almost perfectly match the changing hormonal levels, the sex steroids as they ride sharply through puberty and then decline slowly as you age. Bottom line is that somebody in their late 50s, early 60s will want to go to bed about two hours earlier than when they were in their late teens, early 20s. So it’s a two hour, it’s a big effect. So we’ve got genes, we’ve got age. And then as we discussed, it’s that when you see light, so morning light advances the clock, makes you get up earlier, and dusk light delays the clock, makes you go to bed later. And so one thing you can do if you’re an owl and you want to become more lark like, then you can set the alarm clock, get outside, get morning light if it’s spring, summer, or sit in front of a light box, get that photon shower in the morning, and that will nudge your clock forward in time, making it easier to get up.
The other thing that’s really important is that people who are tired during the week, they’re not getting the sleep they need then tend to oversleep at the weekends. And then they miss morning light on a Saturday or a Sunday morning and therefore the clock drifts to a bit of a later time ’cause it’ll get the afternoon light but not the morning light. And so getting up on the Monday is much more tricky for somebody who’s oversleeping at the weekend to try and catch up on their sleep. But chronotype is really important, genetic component. It’s got an age component. And the third component is when you see light. Now, those biological factors, of course can be exaggerated by smartphone use and as we’ve discussed, endless smartphone use, you know, keeping you awake and giving you those shortened night experiences.
Brett McKay: I wanna dig more into how our understanding of circadian rhythm can help us improve our sleep, ’cause I’ve been experiencing this this year. So I turned, I’ll be, I’m turning 42 this year, and starting at the beginning of this year, my sleep just started changing. It was really weird. For the longest time I could go to bed about 10:30 and wake up about 7:00, never wake up in the middle of the night. But starting this year, I started waking up at 6:00 and then 5:30 and then 5:00 and I started waking up in the middle of the night. I was like, what is going on here? So what is going on? Why is it as we get older you can’t sleep as long and you wake up more often?
Russell Foster: Yeah. There’s a couple of things that are being integrated here. First of all, you’re in your 40s and that’s probably the most demanding period of one’s life. You are dealing, I dunno, in your personal circumstances, but you know, it’s job, career, possession, it’s partnerships, it’s relationships. It may be kids, it may be family. All of those sorts of things tend to crash in on you in your 40s and provide, you know, added levels of stress and anxiety. Which means if you wake up, you are sort of be flooded with all of these thoughts, and it’s more difficult to get back to sleep. But actually, the norm for humans is indeed to wake up, and then fall back to sleep again. And so for example, it’s well described in the Richard Ekirch, for example, has looked at the literature in the pre-industrial era where people have described, I had a wonderful first sleep, but my second sleep wasn’t as good or whatever.
So bimodal sleep was the norm, and people sort of woke up and then they went back to sleep again. And in fact, studies based upon Richard’s work have taken youngsters into the lab, given them the opportunity to sleep for 12 hours, and be awake for 12 hours. So a 12 hour light-dark cycle, and they flipped to being bimodal in sleep. They fragmented their sleep. So it’s nothing to worry about if you wake up during the night, it’s normal. The key thing is to realize if you stay relaxed, and if you stay calm, you will get back to sleep. It may not happen instantly, but it will happen. What I do is I listen to, in the UK we have a Radio 4 Extra, which has got lots of plays and stories and short bits, biographies. And I can listen to one of those things and then fall back to sleep very, very quickly. Other people, they may need to get outta bed for 20 minutes, 30 minutes and then relax and get back to sleep.
The thing that we’ve sort of said previously is that the great enemy of sleep, and the great… Most people don’t have a sleep problem. They have a stress or an anxiety issue. And so that’s why it’s so absolutely vital that if you’re not getting the sleep that you want, you have stress management and relaxation procedures that will almost always allow you to get back to sleep. Now one other thing is that as we age, the circadian drive for sleep is not as robust. The drive isn’t as as ferocious as it were. And so the distinction between day and night isn’t quite as crisp, which means that the structure of sleep will be slightly altered as you age. And so yeah, there are physiological changes which underpin our ability to not get the sleep we had earlier in our earlier life. But the key thing is that different is not necessarily bad. And it’s all about enjoying the sleep that we get, and not worrying about the sleep that we had when we were 30.
Brett McKay: Okay. I like that because I was so used to getting seven to eight hours of sleep. Now I’m getting seven to maybe six and a half hours of sleep. And I’m not like, I don’t feel tired during the day when I get six and a half hours of sleep. It’s just like, wow. So I’ve just gotta get used to it. It’s fine.
Well, that’s it. Yeah. And not get panic about it. And I think you’ve raised a really important point, because how do we know if we’re getting enough sleep? Well, do you feel that you can perform at your peak during the day? Do you oversleep extensively on free days? Particularly if you go on holiday, how’s your sleep pattern changed? Do you need an alarm clock or somebody else to get you out of bed? Does it take you a long time to wake up? Are you feeling groggy, for example? And do you feel sleepy and irritable when you’re awake? Do you crave a nap? Is your, we’ve touched on this, is your behavior overly impulsive? And do you crave caffeinated drinks? And of course, it’s listening to your partners, your friends, your family, your work colleagues, are they saying, you know, you seem a bit more irritable, you don’t have the same empathy. You seem to be doing stupid and unreflective things. This is all telling us we’re not getting the sleep we need. And we do need to listen to others. I think there’s a tendency to be a little bit defensive about our sleep. And I think actually it’s great. If people are saying these things, it’s important we should listen.
What about, you talk about this in the book, peeing in the middle of the night, having to wake up and go pee. What’s going on there?
Russell Foster: Well, that’s, there’s lots of interesting stuff there. But we talked about this dampening of the circadian drive for sleep, but it’s a dampening for a whole bunch of things. So the hormones underpinning urine production aren’t as, you know, urine production during the day, nothing at night. Well, that kind of gets a bit sloppy, so you are more likely to produce urine at night. And there’s two other factors here. If you are sitting in a chair all day, then blood will tend to, you get your puffy ankles or your lower legs tend to fill with fluid, with blood, and then you lie down and that blood is then integrated back into the body. What’s fascinating is that by just simply lying down, and by sitting all day, you can produce, you could, that you need to get rid of that fluid. And so you can produce as much as a liter of urine simply by lying down after a day of sitting.
The other thing is that people are who are on anti-hypertensives, sometimes these hypertensives make you pee a lot. They just try and get rid of blood volume to reduce blood pressure. And so, you have to be a little bit careful about those hypertensives, which can make urine production worse. The good news is that there are drugs that mimic the natural drugs that produce urine at particular times. And you can take those, vasopressin, which stops urine production when you’re trying to sleep at night. Yeah, it’s a common problem. Many people do it and many people sort of buy a little bottle that they pee into by the bed so they don’t have to go to the loo. I mean, you know, there’s lots of strategies. And in fact, as an aside, as I think I mentioned in the book, those people that do pee into a bottle overnight, they collect their urine because it’s good for the garden. You have to dilute it a bit if you’re gonna put it straight onto the soil, but you can put it straight into your compost heap and it works a treat.
Brett McKay: Yeah. And I imagine also if you want to avoid it, just try not to drink as much fluid before bed.
Russell Foster: Yeah, well, absolutely. Yeah, absolutely. I mean, and these are sort of tricks and, you know, that nighttime cup of tea or whatever, just try and move it earlier and get it peed out before you actually go to bed.
Brett McKay: So we’ve been talking about the circadian rhythm and sleep, but circadian rhythm also governs our metabolism, how our body uses energy. So tell us about that, the circadian rhythm and metabolism.
Russell Foster: Yeah, this is a really interesting area. So what you’ve got is a nighttime metabolism and daytime metabolism. So if we think about daytime, we are taking in calories and we’re burning those calories as we take them in. So daytime metabolism is completely different of nighttime metabolism, which is, we don’t feed, we don’t eat at night, we’re mobilizing stored calories. So they’re very different metabolic states. And what’s turning out to be fascinating is that the way that we process food changes across the day. So if you’re taking glucose, food in the morning and at lunchtime you’re actually metabolizing that glucose very effectively. But as you approach nighttime, you don’t metabolize that glucose effectively. And what happens is it gets turned to stored glucose, either in the liver or laid down as fat. And so it’s very important to concentrate your food intake during the morning and at lunchtime rather than late into the evening.
The problem is, of course, with changing work habits. In the old days we used to live and work during the same space. Now people may spend two hours getting to work and then coming back. There’s no time for a breakfast, there’s a sandwich over lunch, a quick sandwich over lunch. And then finally you get home ravenously hungry, you stuff things into the microwave and you’re eating high fat, high sugar ’cause that’s what you are craving. ‘Cause you haven’t had calories during the day and you’re hungry and you crave actually the worst kind of stuff. But then you are calorie loading at the end of the day and it’s much more likely to be laid down to fat and predisposing to metabolic abnormalities and things like diabetes too, which also raises some interesting issues about when we should exercise.
So there’s a couple of strategies here. So if you exercise in the morning before breakfast, you are still in the nighttime mode of metabolism where you’re burning up stored calories. The problem is that the power that you can exert for exercise isn’t as great first thing in the morning. It rises throughout the day. So a short, 20 minute exercise bout can be really good at burning up a few of the stored calories that you may not want. But then later in the day, when your core body temperature has risen, means that you can exercise for longer and with more power. And so the calories that you’ve taken in during the day can be burnt up more effectively by late afternoon, early evening exercise. You don’t wanna exercise too late because that will raise core body temperature and a higher core body temperature makes it more difficult to get off to sleep at night. So the bottom line with metabolism and exercise is that try and concentrate your calories during the first half of the day. Breakfast and lunchtime, light evening meal, an exercise first thing in the morning, short bout before breakfast, burning up stored calories, and a later more vigorous set of exercises to burn up calories you’ve taken in during the day. And you’ll be able to exercise with greater vigor later in the day.
Brett McKay: Okay. Yeah, that nutrition advice reminds you of that saying, eat breakfast like a king, lunch like a prince and dinner like a pauper.
Russell Foster: Yeah, Yeah, absolutely. And it really is what I think that’s what, a couple of hundred, maybe even a a thousand years old advice. And it’s still true today. And it’s worth bearing in mind how our eating habits have changed. I mean, my grandparents, for example, my grandfather would come home for what they called dinner, which was lunchtime. And that was the main meal of the day. You know, it was a decent breakfast, classic English breakfast followed by a large lunch and then a light tea. And so we’ve changed because of our working habits, when we take our calories in, in, you know, sort of 100 years, less than 100 years.
Brett McKay: I think I’ve noticed, done some observations with my own metabolism and how it’s connected to my circadian rhythm. I did this continuous glucose monitor a while back ago. And one thing I noticed is if I ate a lot of carbs first thing in the morning, like very first thing in the morning, my glucose spiked significantly. But if I shifted things a little bit, if I took those carbs and like ate them a little bit later, it wasn’t as high. It was blunt. And I think it’s ’cause like my body was still waking up. So shifting my carbs later in the morning instead of having first thing in the morning did better for me.
Russell Foster: Well, what’s happening of course, is that first thing in the morning, you’ve got a spiking cortisol. And what cortisol does is prepare you for activity. So it will release, it rises naturally under the influence of the circadian rhythm. And that will increase heart rate, increase glucose into the circulation. So you do get a peak, a spike in the morning of glucose under the regulator probably being driven by cortisol.
Brett McKay: Is there anything… A lot of people have been talking about lately is that your caffeine consumption? Like you should wait a little bit before you have your coffee or tea in the morning, anything to that?
Russell Foster: Well, I don’t have any data to hand really. I mean, personally I drink coffee first thing in the morning. I find it useful to wake me up a bit. And particularly, I think if people are tired, then that morning coffee can be really helpful to increase alertness during the morning commute, for example. But I think the key thing about coffee for me is that you try not to drink it after two o’clock in the afternoon. I’m really sensitive to coffee. So coffee in the evening will actually keep me awake, so I try and cut it out earlier.
Brett McKay: Yeah. That’s another observation I’ve made as I shifted into midlife. Before my 20s and 30s, I could have a caffeinated soda at dinnertime. No problem. I could go to sleep like a baby at 10:30, 11 o’clock at night. Now if I have a caffeinated soda after 2:00 PM, I can’t sleep. I have a hard time falling asleep, that’s interesting.
Russell Foster: Yeah. And it’s one of those things of aging and, of course, it’s the way we process caffeine. I mean, the thing about caffeine, which is so interesting of course, is that, you know, we’ve talked about the circadian regulation of sleep, but there’s another timer which is called the homeostatic driver for sleep or sleep pressure. And it basically means the longer you’ve been awake, the greater the need for sleep, the greater the sleep pressure. And one of the substances that builds up while we’re awake is adenosine. And adenosine is a signal for sleepiness. Now what happens is that caffeine blocks the receptors in the brain that respond to adenosine. That’s why we feel genuinely more alert because the body’s signal saying we’re tired is being blocked by caffeine.
Brett McKay: That’s interesting. The last thing I wanna talk about, you’ve done some research and highlighted research in this book about our circadian rhythm and immune system. So how is our immune system influenced by our circadian rhythm?
Russell Foster: This is so fascinating. The more we dig in, we’re finding that so many I really important systems are being influenced by the circadian system, not least the immune system. And so what was being discovered is that vaccination at different times was having different effects. The classic study was on elderly individuals with the flu vaccine showing that if you have the flu vaccine in the morning, it was three times more effective in generating an antibody response than if you took it in the late afternoon. And so we now know, and this fits beautifully with the idea that the immune system is turned up during the day and it is turned down whilst we’re asleep at night. And you could ask, well, why would you not have the immune system on at full throttle all the time? And the argument we don’t know, but the argument seems to be that one of the great problems of having an immune system is that you can get autoimmune responses where the immune system attacks the body, its body. And so the thought is that you turn it up during the day when you’re moving around meeting other people and you’re in the environment and you’re more likely to encounter pathogens in the environment, but you turn it down at night when you’re not mobile and far less likely to encounter pathogens. And by doing that, you’re much less likely to trigger autoimmune responses. We don’t know that for sure, but that’s the working hypothesis.
Brett McKay: Does our circadian rhythm affect how medication is processed by the body?
Russell Foster: Oh yes. Huge impact. I mean, it really is extraordinary. And so you can get massive time of day effects. So, sort of pioneers from the states, Bill Roeske, has shown that taking anti-cancer drugs at particular times, it’s classic studies he did on ovarian cancer with the same drug but given at different times, in ovarian cancer after five years, one group survived, 45% of the group survived versus 10% in the other group. So the same drug, same concentration, different time, massive impact upon long-term survival. Another study on kids with leukemia looking at chemotherapy showed that after about six and a half years with the evening treatment of the cocktail of drugs, 75% were still alive. Whereas for the morning cocktail of drugs, it had dropped to 35%. Same drugs, same concentration, different time. So lots of data in anti-cancer drugs, same for radiotherapy, incidentally, depends upon the drug and it depends upon the treatment.
So there’s no one rule fits all there. Another really interesting area is in once, high blood pressure and taking, when do you take a anti-hypertensives? There’s a dangerous window between 6:00 AM and 12 noon when there’s a 50% greater chance of having a stroke, for example, than any other time of the day. So when do you take your antihypertensives that blunt, that sharp rise in morning blood pressure? Well, you know, without thinking about it, you might say, well, I take it in the morning. But of course the time you’ve got up, you’ve taken the drugs and the time they’ve reached the circulation, you’re probably past that danger window, that spike. And some studies from Spain showed that those individuals who took their antihypertensives before bed had a 50% greater chance of survival over a 10-year period than those that took their antihypertensives first, you know, when they woke up, which I think is really interesting. And of course, that’s based upon the fact that the antihypertensives hang around in the body. They have a short half-life. So by taking them before you go to sleep, they’ll be at a high level still in the morning when that sharp rise in blood pressure occurs, which is one of the drivers for producing a stroke. But if you, as I say, if you take it after you’ve woken up, then the time the drug is actually taken into the body, you’re past that danger window.
Brett McKay: Well, Russell, this has been a great conversation. Is there someplace people can go to learn more about the book and your work?
Russell Foster: Yeah. I mean, Lifetime is available in the United States published by Yale University Press. UK it’s by Penguin. And most of the discussion that we’ve had is in Lifetime. And also, if you’re interested in our website, which I have to say like most websites, need a bit of updating, you just go to the Sleep and Circadian Neuroscience Institute, University of Oxford, and you’ll find us. And also if you do a Google for me, you’ll see some podcasts and stuff online. And if anybody’s really interested and has specific questions, we can always sort of ping you the papers that you’re interested in. I should say about Lifetime, one of the great things by working with Penguin is that they didn’t kick back about including citations, references. So the science is accompanied by the scientific paper that supports that statement. So it sounds really intimidating that there are 920 references in the book, but that, it’s turned out to be fantastic.
You know, members of the public have said, thank you so much for treating us as adults. *f you want to dig deeper, the information is there. And I had one very amusing email from a person who said, yes, I was telling my husband about, in fact, it was when to take his hypertensives. And he said, “Oh, that’s complete nonsense.” And she said, “Go to the reference in the book.” He did. And he was convinced that he should change his behavior. So I think what the book tries to do is provide the science and then people can make choices based upon the science about what they want to do. And I should just finish, I mean, part of the message in Lifetime is that one shoe size doesn’t fit all. And partly one of the reasons I wrote it was ’cause I was absolutely fed up with sort of the sergeant majors of sleep screaming, you must get eight hours, you shouldn’t look at a Kindle, you can’t do this, you can’t do that. Sleep is a highly dynamic, very flexible behavior, and it’s all about deciding whether you’re getting the sleep that you need and using the science to nudge you and advise you where you feel that things might need a change. But it is absolutely not somebody screaming at you, you must do this and that.
Brett McKay: Well, Russell Foster, thanks for your time. It’s been a pleasure.
Russell Foster: Well, absolutely great to chat, Brett, and when you’re coming out to the UK next, I hope we can get together.
Brett McKay: Sounds great. My guest today is Russell Foster. He’s the author of the book Lifetime. It’s available on amazon.com and bookstores everywhere. Check out our show notes at aom.is/circadian where you can find links to resources, we delve deeper into this topic.
Well, that wraps up another edition of the AOM podcast. Make sure to check out our website at artofmanliness.com where you Find our podcast archives as well as thousands of articles that we’ve written over the years about pretty much anything you think of. And if you haven’t done so already, I’d appreciate it if you take one minute to give a review on Apple podcast or Spotify, it helps out a lot. And if you’ve done that already, thank you. Please consider sharing the show with a friend or family member who you think will get something out of it. As always, thank you for the continued support. Until next time, this is Brett McKay reminding you to not only Listen to AOM podcast but put what you’ve heard into action.
