Unlock Better Sleep and Health by Harnessing Your Circadian Rhythm
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Summary
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 Role 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 harm that can accrue from working the night shift, and what can be done to mitigate them.
Transcript
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Brett McKay here, and welcome to another edition of the Art of Manliness podcast.
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You probably know your body follows a circadian rhythm and probably think of it as primarily
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regulating your sleep-wake cycle, which it certainly does.
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But your body's internal clock also regulates many other physical, mental, and behavioral
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And working with your circadian rhythm, rather than against it, can boost your health and
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Here to unpack how to do so is Russell Foster, professor of circadian neuroscience and the
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author of Lifetime, Your Body Clock and Its Essential Roles in Good Health and Sleep.
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In the first part of our conversation, we discussed some science and background on circadian rhythm
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We then turned to the practical implications of having an internal clock, including whether
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you need to worry about viewing blue light at night, the significant mental and physical
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harms that can accrue from working the night shift, and what can be done to mitigate them,
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what influences your chronotype, and whether you're a morning lark or night owl, whether
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you should be concerned if you're waking up in the middle of the night, why you wake up
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to pee in the night, the best times of day to exercise, and how the circadian rhythm can
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After the show's over, check out our show notes at awim.is slash circadian.
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All right, Russell Foster, welcome to the show.
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So you have spent your career researching circadian rhythms, our internal clock that governs our
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physiology and we'll learn about today, our mood and other things as well.
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Well, I didn't get into circadian rhythms to begin with.
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I mean, I went to university thinking I would become a marine biologist because I loved animals,
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So duh, you know, it's obvious I was into marine biology.
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Then I discovered physiology in my second year at university and found that fascinating, and
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particularly how photoreceptors, light sensors work.
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And I became really obsessed with, first of all, the pineal photoreceptors of tadpoles.
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And you can record from this third eye, light responses.
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And in fact, when you dim the lights, it would trigger a swimming response.
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Then for my PhD, I was working on the photoreceptors in birds that measure day length,
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and that triggers their reproductive responses.
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So as the day lengths increase during spring, it triggers reproduction.
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And I was, you know, fascinated about, well, what's detecting that light?
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How do they measure the length of light versus dark?
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And that then got me into sort of the circadian field proper, which is what receptors in the
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eye of mammals, creatures like you and I, are detecting the light-dark cycle for the regulation
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And at that point, it was simply assumed, well, we knew it was the eye, but it was assumed that
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And we should, I know we're going to talk about the weird photoreceptors in the eye later,
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but really it was a passion for light-sensing systems that got me into clocks.
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And then along the way, you became a sleep researcher too.
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And that was fascinating because I was working at Charing Cross Hospital at that point as part
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And I was in an elevator with a psychiatrist and he said, oh, you know, you work on sleep,
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And he said, well, my patients with schizophrenia have terrible sleep.
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So they go to bed late, get up late, miss my clinic and don't have friends.
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And I thought that was one of the most stupid things I'd heard, but it triggered an interest
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in, well, what is going on with those individuals?
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So hooked up with another psychiatrist and we looked at her subjects, her patients with
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And we measured really for the first time their sleep-wake profiles.
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And what became really extraordinary for me is that their sleep-wake patterns were absolutely
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And so I sort of then moved into humans and sleep research, combining both a knowledge
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of circadian rhythms, these internal 24-hour body clocks, and how circadian rhythms in turn
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Well, let's talk about the circadian rhythm in our internal clock.
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So scientists have noticed for millennia that humans and other animals have a bodily schedule.
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We want to wake up at a certain time and go to sleep at a certain time.
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And for most of that time, they thought it was just light that was driving that.
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We're going to talk about that, your research in photoreceptors.
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But then scientists discovered that we have an internal clock that ticks independently of
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How did scientists discover this internal clock?
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Well, with all good biology, it started with good observation.
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And back in 1729, I think it was, there was a French sort of scientist and de Marien, and
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he was studying the movements of leaves of a plant called mimosa.
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Many of your listeners may be aware of this plant because it's that plant where you touch
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And what happens with those mimosa, and they really, it's really worth having one of these
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in the house, is that you see that the plants' leaves open during the day and they close at
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And of course, the assumption was this is driven by the changing light levels.
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And so what de Marien did was put these plants in a light tight cupboard and then sort of would
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peek in at different times and see what the leaves are doing.
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And to his astonishment, the leaves continue with this opening and closing movement under
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And that's one of the key criteria of identifying a circadian rhythm, something that persists with
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a rhythm of about 24 hours under constant conditions.
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Now, those early experiments by de Marien had a potential flaw in that he controlled for light,
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So Candol, about 100 years later, took these mimosa plants down to a salt mine.
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Constant darkness and critically constant temperature.
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And observed again, these opening and closing of leaf movement.
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And so this was the first, and it was in plants, not in animals, where circadian rhythms were first
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sort of observed quantitatively rather than just sort of anecdotally.
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How did they discover that humans had this similar thing?
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Well, I suppose one of the first experiments, analogous to those plant experiments, was in Mammoth
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Cave in Kentucky, where two researchers went down.
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And they showed that sleep-wake cycles would continue under conditions of constant darkness
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But then work stopped, really, during the Second World War.
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But after that, a chap called Ashoff in Germany built some bunkers where you could control light
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And then started to systematically, in the 1960s and 70s, study human rhythmicity under broadly
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Okay, so we have an internal clock that keeps us to a roughly 24-hour schedule.
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And that clock works even if we're cut off from external stimuli.
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So if you put yourself in a temperature-controlled, light-controlled room, your body will stay
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But without external stimuli, it's not going to match the day-night cycle.
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So for our circadian rhythm to line up with that day-night cycle, this is called entrainment,
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it needs external stimuli, the most important of which is light exposure.
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So what role does light play in our circadian rhythm?
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Yeah, I think it's probably good just to step back a bit and sort of think about what our
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And what we need to do is deliver the right stuff at the right concentration to the right
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tissues and organs at the right time of the day.
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And it's the circadian system that gives this time structure for life.
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But it's no good having a clock ticking away, fine-tuning our biology to the varied demands
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of the rest activity in the light-dark cycle, unless it's actually entrained or locked onto
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And the most powerful signal is the dawn-dusk cycle.
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And this is where I sort of got into circadian rhythms, because I was fascinated.
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We knew that in the mammals that the receptor was in the eye, because if you have no eyes
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as a result of a terrible accident, then your sleep-wake cycle, you get up later and later
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and later each day, you're drifting through time.
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So it's by an average, let's say, of 10 to 15 minutes each day, you're getting up later.
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Or if you are in complete darkness, you again show that drift.
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But the thing that puzzled me is that how can it be that the visual cells, the rods and the
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cones, can also be used for circadian light detection?
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What I mean by that is what a visual cell has to do is grab light in a fraction of a second
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and forget it's seen that light to give you a crisp image of our world.
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What the circadian system needs is an overall impression of the amount of light at dawn and
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And this can be gathering light information over minutes and sometimes hours.
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And I couldn't see how visual cells could provide that time-of-day information.
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So we started working on mice with hereditary retinal disorders where the rods and the cones
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They had their eyes, but they were visually blind.
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And so we decided to put them in running wheels, you know, a little running wheel in the cage
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and monitored when they would start their activity and end their activity under a light-dark cycle.
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And to our astonishment, these mice could regulate their circadian rhythms.
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Not only could they do it, but they did it with the same sensitivity as those mice with
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So there was something else in the eye because if you covered the eyes up, this response to
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light would cease and the mice would start to drift through time.
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And so this then led to the hunt for what this third receptor might be.
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And we were able to show this in mice and Dennis Dacey was able to show this in monkeys and
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others were able to show it in other groups of animals, that there's this third receptor
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in the eye, which we've called photosensitive retinal ganglion cells.
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And what they are is that there are multiple layers within the retina, that part of the eye,
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And beneath the rods and cones, there's the inner retina, which does some processing of the
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And then they send that information to the ganglion cells.
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And the ganglion cells have these long axons, which project from the eye into the brain to
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And what turned out to be, and it's still, I think it's still extraordinary, is that these,
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there's 1% or so, depends on the species, but certainly a small number of those ganglion
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cells are directly light sensitive using a blue light sensitive photopigment called melanopsin
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And so, yeah, the eye is not only the organ of space, because it provides us with our sense
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of vision, but it's also, in a sense, the organ of time, because it can coordinate the
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external light dark cycle with the internal day and make sure that everything is synchronized.
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So we're doing the right thing at the right time.
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So the big takeaway there is there's a third receptor, photon receptor in our eye, not
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So you could be blind and still be synced up with the dong dust cycle.
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So we, I was in a seminar and an ophthalmologist was talking about his studies on an elderly
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lady who had no apparent rods and cones as they were able to detect.
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And so I said to him, you know, in the question time, well, what's her sleep wake cycle like?
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So anyway, we worked with this ophthalmologist and discovered that this lady with no conscious
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light perception was still able to regulate her rest activity cycles perfectly normally.
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And so, and we were able to work out that it was those photosensitive retinal ganglion
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We were also able to show in that individual that these new photoreceptors do more than
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They seem to provide a generalized measure of environmental brightness to, for example,
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Part of our pupil constriction is actually being regulated by those photosensitive
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We also asked this lady if she had any conscious detection of light.
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But Dennis Stacy had shown that these PRGCs in a monkey project to some of the visual
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So we thought, well, maybe she's got some subconscious ability to detect light.
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When we turn the lights on and then off for a period, and we asked her whether the lights
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on or off, she could always tell when the lights were on and off, even though she had
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So really that and more studies in mice have shown that these receptors do a heck of a lot
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of brightness detecting tasks, including regulating levels of alertness, even heart rate in some
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And indeed, it looks as though they're contributing to mood.
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So increase levels of light, you can increase alertness, and you can also alter mood.
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So yeah, it's turned out to be something quite extraordinary.
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How can the timing of our light exposure influence our circadian rhythms?
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That is, if we got exposed to light earlier in the day, will that affect our circadian rhythm
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Well, that's a really key point, Brett, because morning light advances the clock.
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It makes us get up earlier and go to bed earlier.
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Now that's important because light during the middle of the day is not having too much
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And we've shown in university students around the world that those who are owls, they have
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They were missing morning light, which would advance the clock, but they were getting the
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late afternoon, early evening light, which would shift them to a later time.
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So when you see light can be incredibly important in influencing whether you want to get up late
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Like I wake up, I wake up early and I'm exposed to light during my morning walk.
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And then I, sometimes I'm out at dusk and getting light exposure there.
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What does that just kind of balance things out?
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And in fact, when we were all agricultural workers and, you know, up until 1800, more than
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90% of the population were agricultural workers getting symmetrical dawn-dusk exposure.
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And so we stayed beautifully on cue, rose with the sun and went to bed with dusk.
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And in fact, artificial light was really expensive up until the 20th century.
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I mean, in the 19th century, a candle, which actually isn't very bright and wouldn't have
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had much effect on the clock, was the cost of a working man's daily wage.
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And so people just synchronize their biology with the dawn-dusk cycle quite naturally.
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So lately, there's been a lot of talk about how viewing blue light from our digital devices before
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Or if you're going to use it, turn your screen yellow.
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I mean, this is a rapidly moving field, but what's happened in the past few years.
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So the early studies looking, for example, at a Kindle, and people were asked to look at
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a Kindle on its brightest light setting for four hours on five consecutive nights.
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And that delayed sleep onset just statistically significantly by nine minutes.
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But it did have an effect upon the rhythms of melatonin.
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And so this sort of got into the literature and the press as, oh, well, reading a Kindle
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before you go to bed is a disaster for your circadian rhythms.
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And of course, it had a tiny effect on sleep-wake.
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And instead of people being kept under dim light before the evening Kindle use, they gave
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them bright light, about six hours of bright light, say about 500 lux during the day.
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And that bright light exposure completely abolished any subtle effects of light in the evening.
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These are great experiments that were done, the initial ones on the Kindle, but they were
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They didn't take into account the real-world situation.
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And if you're getting moderate levels of light during the day, you're not going to be sensitive
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to dim light or so sensitive to dim light in the evening.
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So that was one of the studies that has been overturned.
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There's been recent reviews looking at the use of yellow-blue-blocking glasses on behavior,
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And indeed, these screens that shift from blue-enriched light to red-enriched light,
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the efflux computer programs, have also been shown to have no effect upon circadian biology
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So it's one of those things where, you know, we discovered that these photosensitive retinal
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ganglion cells are maximally sensitive to blue light.
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And people have said, ah, well, it'll be blue light that will be important for disrupting
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these receptors and the circadian system in the evening.
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But the key thing that's not really appreciated is that these receptors need quite a bit of
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And the impact of that light will depend upon how much light you've seen during the day,
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And so it's turning out to be a very complicated signal that's being integrated by those receptors
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Bottom line is, we don't have any strong evidence that blue light, as sort of the levels that you
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get from computer screens and all the rest of it, will actually disrupt your sleep in the evening.
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But remember, these receptors need bright light for a long period of time.
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That's the other thing about the experiments in the lab.
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They've looked at not just a small exposure, a short duration exposure, but people have
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been given six or seven hours of light exposure.
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And you need those long effects with dim light to get any sort of shift in the circadian system.
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So what the circadian system is doing is integrating light over long periods of time to get an effect.
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Okay, so you can throw away your yellow-orange glasses.
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I mean, I just think it's, yeah, and there's a whole industry that's sort of built around that sort of stuff.
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What about just exposure to artificial light in the home at nighttime?
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And again, we don't fully know because the experiments have been extrapolated from lab experiments where
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people have been kept under relatively dim light and then exposed to dim light in the evening.
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And they've been exposed to durations of light for six, seven hours.
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Whether that can map on to the real world, we don't know.
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But there are estimates suggesting that, you know, about 100 lux, which is not very much light,
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with six and a half hours of exposure, can have a bit of an effect upon the clock.
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Some studies from Australia have shown that the sensitivity of the clock between individuals
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And we know that the clock is getting less sensitive as we age.
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And at the moment, we don't have the evidence base for hard recommendations about light exposure
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It makes sense not to get bright light exposure in the evening because that will delay the clock.
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But how bright that light should be and for how long and for what color or wavelength,
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So, you know, rule of thumb, minimize light exposure, you know, in the evenings.
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But you can certainly read your Kindle, you can look at your computer without worrying too much.
00:21:04.880
And I think you mentioned in the book, the thing you got to worry more about with your
00:21:08.040
smartphone or your devices, it's not the light, it's just that it stimulates your brain a lot.
00:21:16.340
And of course, the great enemy of sleep is anxiety and stress.
00:21:20.440
And yeah, looking at social media or doing emails or whatever is going to increase your alertness
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And that will undoubtedly delay your sleep onset.
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So that's the problem with, you know, with social media and why I think most of us would
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recommend not using these smartphone devices or stuff like that before you go to bed, because
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Now, of course, you can use a Kindle for your relaxing book, your few pages of Jane Austen or
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whatever it is that relaxes you and gets you off to sleep.
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That's not a worry, but it's the sort of interactive stuff and the stress that you get from work emails
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We're going to take a quick break for your word from our sponsors.
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What happens when we unsync our bodies from the usual wake during the day and asleep during
00:22:13.900
And of course, there can be short-term and long-term effects of night shift work.
00:22:20.060
So the sort of thing that we see with relatively short levels of disruption, of sleep and circadian
00:22:26.080
rhythm disruption scarred, are our emotional responses.
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So fluctuations in mood, irritability, anxiety, loss of empathy.
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What's so fascinating that the tired brain is not good at picking up the sort of social signals
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for other individuals and reading what their moods and their emotions are like.
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I think another fascinating one is risk-taking and impulsivity.
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We're much more likely to do stupid and unreflective things.
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Yeah, I'm sure I can go through that traffic light before it goes red, for example.
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Some very interesting studies from Germany have shown that the tired brain remembers negative
00:23:08.060
So tired people, you know, their whole worldview is being influenced by the stuff that they
00:23:16.460
You're also much more likely to use caffeine to drive you through the waking day and then
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try and reverse the effects of caffeine with sedatives, such as alcohol or sleeping tablets,
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both of which do not provide a biological mimic for sleep.
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They don't, you know, actually help you get to sleep.
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So that's some of the emotional responses, cognitive responses.
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So our whole ability to function, to come up with novel solutions to complex problems
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So to extract from all the bits of information that we're being bombarded with constantly,
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So multitasking falls apart, memory consolidation, information processing, concentration, decision
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making, all those sorts of attributes that make us such a special productive creature
00:24:11.460
And then if we move on to the sort of impact on physiology and health after years of night
00:24:18.600
So we have increased levels of cardiovascular disease, altered stress responses.
00:24:24.600
It seems that we override the chronic need to sleep by activating the stress axis.
00:24:30.240
And what activation of the stress axis will do will be, of course, to increase blood pressure.
00:24:38.940
You're releasing more glucose into the circulation.
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So that's going to have metabolic problems, you know, increasing levels of blood glucose,
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predisposing to type 2 diabetes, lowered immunity.
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The one thing we know about high levels of the stress hormone cortisol is that it will reduce
00:24:54.780
the effectiveness of the immune system, which is why you have higher rates of cancer and
00:25:01.980
And in fact, the World Health Organization has now said that night shift work is a probable
00:25:06.900
carcinogen because of the higher rates of cancer you get in night shift.
00:25:11.500
Particularly the studies that have convinced the community has been on nurses, you know,
00:25:16.760
nurses doing night shift work 15, 20 years have higher rates of colorectal cancer and breast
00:25:22.100
And that's controlling for smoking and all the other factors.
00:25:25.340
Oh, and the other thing I should mention, of course, is really important in terms of if
00:25:29.960
you are vulnerable to depression and psychosis, lack of sleep can shift you and disrupted sleep
00:25:36.340
can shift you into that depressive or psychotic state.
00:25:41.900
We've known for a long time that the poor sleep in the middle years is a risk factor for dementia
00:25:48.860
But we've never had any real sense of what the mechanisms are.
00:25:52.080
And with the discovery of what's been called the glymphatic system, which is sort of a toxin
00:25:58.700
And the glymphatic system is clearing a misfolded protein called beta amyloid.
00:26:04.420
And beta amyloid is a buildup within the brain is associated with dementia, for example.
00:26:09.840
And we know that even one night of no sleep, you can actually detect in the cerebral spinal
00:26:14.980
fluid a sort of a slight increase in beta amyloid.
00:26:18.700
So over years of not sleeping well, you're going to get a buildup in beta amyloid, which is going
00:26:25.640
Now, I'm not saying that poor sleep is going to cause dementia, but if you are vulnerable
00:26:29.920
to developing dementia, that buildup of beta amyloid is going to nudge you in the wrong
00:26:35.460
So shift work sounds like it's terrible for you.
00:26:38.780
And I, but I think we've got to be realistic here.
00:26:41.140
We're not going to put the 24 seven society back in its bottle.
00:26:44.820
So what can employers do now to mitigate some of the effects on their employees?
00:26:51.120
And I think this is a really important issue because it's no good just sort of saying you
00:26:56.360
Well, we're going to need shift workers for, you know, frontline in hospitals and looking
00:27:00.820
after our transport systems and all the rest of it.
00:27:04.020
So a couple of points I'd make is that one of the, one of the great problems that you
00:27:08.900
have as a shift worker is falling asleep after the night shift on the journey home.
00:27:14.320
And there was a study from the UK showing that 57% of junior doctors had either had a crash
00:27:20.540
or a near miss driving home after the night shift.
00:27:24.040
Well, why not install, you know, apps on your phone, your smartphone, which can detect your
00:27:29.660
head nod or the movement of the car laterally and alert you to the fact that you might be
00:27:35.220
And of course, you know, high end cars now have this technology built in loss of vigilance
00:27:41.460
Well, you could introduce bright light in workstations to increase levels of alertness
00:27:47.360
and make you less likely to fall asleep and have an accident.
00:27:50.720
I think a really, really important point is that, you know, night shift workers have poor
00:27:56.340
So why aren't those vulnerable individuals having higher frequency health checks to detect
00:28:01.460
these problems before they become, become chronic?
00:28:06.860
We see obesity, type 2 diabetes, metabolic abnormalities in night shift workers.
00:28:15.900
It's high fat, high sugar in vending machines or in the cantees.
00:28:20.020
Cantees, nobody, and I think this is extraordinary, as far as I'm aware, is providing our night shift
00:28:25.140
workers with high protein, easy to digest snacks to get them through the night.
00:28:30.060
Failure to appreciate the consequences of night shift by the employee and family.
00:28:33.720
The divorce rate in some sectors can be six times higher for night shift workers compared
00:28:41.440
So we should be, you know, providing this information to the broader family or group that this person
00:28:47.480
is living with, you know, explaining that this person hasn't turned into a monster, but
00:28:51.780
this is a consequence of driving your biology outside of its normal range.
00:28:58.680
And, you know, just to finish on that, this section is that we know that these pathologies get
00:29:04.380
So should we think about limiting night shift work to three to four years on, and then maybe
00:29:11.240
I don't have the data to support that suggestion, but I think it's something we should be looking
00:29:16.060
The problem, of course, is that most people don't want to do night shift work, but they
00:29:22.260
So there's a number of factors that are being integrated here.
00:29:25.180
But I think we could support our night shift community far better than we are currently doing.
00:29:30.820
So you mentioned earlier that there are different chronotypes.
00:29:33.940
So we all follow a roughly 24-hour circadian rhythm, but some of us want to start our day
00:29:45.080
There's three basic components to one's chronotype.
00:29:49.840
So we're now seeing, you know, in those key clock genes that have been discovered, subtle
00:29:54.380
polymorphisms can make you more of a morning person than an evening person.
00:30:02.980
So from about the age of 10, there's a tendency to want to go to bed later and later and later.
00:30:08.760
Women peak at around about 19 and a half, men about 21, and men tend to have a longer,
00:30:17.760
And then from the late teens, early 20s, there's a slow move to a more morning chronotype until
00:30:24.240
you're about, you know, your late 50s, early 60s, and you're getting up and going to bed
00:30:28.420
at about the time you got up and went to bed in your pre-puberty area.
00:30:33.320
And I throw in puberty there because, of course, those changes in chronotype almost perfectly
00:30:38.440
match the changing hormonal levels, the sex steroids, as they ride sharply through puberty
00:30:47.540
Bottom line is that somebody in their late 50s, early 60s will want to go to bed about
00:30:54.640
two hours earlier than when they were in their late teens, early 20s.
00:31:01.480
So we've got genes, we've got age, and then as we discussed, it's that when you see light.
00:31:07.360
So morning light advances the clock, makes you get up earlier, and dusk light delays the
00:31:13.980
And so one thing you can do if you're an owl and you want to become more lark-like, then
00:31:19.840
you can set the alarm clock, get outside, get morning light.
00:31:23.900
If it's spring, summer, or sit in front of a light box, get that photon shower in the
00:31:28.400
morning, and that will nudge your clock forward in time, making it easier to get up.
00:31:33.920
The other thing that's really important is that people who are tired during the week,
00:31:39.380
they're not getting the sleep they need, then tend to oversleep at the weekends.
00:31:42.740
And then they miss morning light on a Saturday or a Sunday morning.
00:31:47.960
And therefore, the clock drifts to a bit of a later time, because it'll get the afternoon
00:31:54.400
And so getting up on the Monday is much more tricky for somebody who's oversleeping at the
00:32:08.260
Now, those biological factors, of course, can be exaggerated by smartphone use.
00:32:13.820
And as we've discussed, endless smartphone use, you know, keeping you awake and giving
00:32:20.360
I want to dig more into how our understanding of circadian rhythm can help us improve our
00:32:28.440
And starting at the beginning of this year, my sleep just started changing.
00:32:33.840
For the longest time, I could go to bed about 1030 and wake up about seven, never wake up
00:32:40.220
But starting this year, I started waking up at six and then 530 and then five.
00:32:45.180
And I started waking up in the middle of the night.
00:32:49.380
Why is it as we get older, you can't sleep as long and you wake up more often?
00:32:54.280
Yeah, there's a couple of things that are being integrated here.
00:32:58.760
And that's probably the most demanding period of one's life.
00:33:02.600
You're dealing, I don't know, in your personal circumstances.
00:33:12.460
All of those sorts of things tend to crash in on you in your 40s and provide, you know,
00:33:19.760
Which means if you wake up, you'll sort of be flooded with all of these thoughts and it's
00:33:26.580
But actually, the norm for humans is indeed to wake up and then fall back to sleep again.
00:33:34.080
And so, for example, it's well described in the Richard E. Kirk, for example, has looked
00:33:39.360
at the literature in the pre-industrial era where people have described, I had a wonderful
00:33:44.280
first sleep, but my second sleep wasn't as good or whatever.
00:33:47.360
So, bimodal sleep was the norm and people sort of woke up and then they went back to
00:33:54.060
And in fact, studies based upon Richard's work have taken youngsters into the lab, given
00:34:00.080
them the opportunity to sleep for 12 hours and be awake for 12 hours.
00:34:11.040
So, it's nothing to worry about if you wake up during the night.
00:34:15.600
The key thing is to realize if you stay relaxed, if you stay calm, you will get back to sleep.
00:34:21.200
It may not happen instantly, but it will happen.
00:34:24.080
What I do is I listen to, in the UK, we have Radio 4 Extra, which has got lots of plays and
00:34:31.480
stories and, you know, short bits, you know, biographies.
00:34:34.940
And I can listen to one of those things and then fall back to sleep very, very quickly.
00:34:39.660
Other people, they may need to get out of bed for 20 minutes, 30 minutes, and then relax
00:34:46.500
The thing that we've sort of said previously is that, you know, the great enemy of sleep
00:34:50.380
and the great, you know, most people don't have a sleep problem.
00:34:55.380
And so, that's why it's so absolutely vital that if you're not getting the sleep that you
00:35:01.040
want, you have stress management and relaxation procedures that will almost always allow you
00:35:09.100
Now, one other thing is that as we age, the circadian drive for sleep is not as robust.
00:35:15.860
You know, the drive isn't as ferocious as it were.
00:35:18.780
And so, the distinction between day and night isn't quite as crisp, which means that the
00:35:23.980
structure of sleep will be slightly altered as you age.
00:35:27.600
And so, yeah, there are physiological changes which underpin our ability to not get the sleep
00:35:35.420
But the key thing is that different is not necessarily bad.
00:35:39.800
And it's all about enjoying the sleep that we get and not worrying about the sleep that we
00:35:47.480
Because I was so used to getting seven to eight hours of sleep.
00:35:50.780
Now, I'm getting seven to maybe six and a half hours of sleep.
00:35:54.940
And I'm not like, I don't feel tired during the day when I get six and a half hours of
00:36:02.780
And I think you've raised a really important point because, you know, how do we know if we're
00:36:07.240
Well, do you feel that you can perform at your peak during the day?
00:36:11.260
Do you oversleep extensively on free days, particularly if you go on holiday?
00:36:17.740
Do you need an alarm clock or somebody else to get you out of bed?
00:36:25.280
And do you feel sleepy and irritable when you're awake?
00:36:30.180
Is your, we touched on this, is your behavior overly impulsive?
00:36:36.360
And of course, it's listening to your partners, your friends, your family, your work colleagues.
00:36:41.680
You know, are they saying, you know, you seem a bit more irritable.
00:36:45.660
You seem to be doing stupid and unreflected things.
00:36:48.700
This is all telling us we're not getting the sleep we need.
00:36:52.800
I think there's a tendency to be a little bit defensive about our sleep.
00:36:58.260
You know, if people are saying these things, it's important.
00:37:01.940
What about, you talk about this in the book, peeing in the middle of the night,
00:37:09.120
But, you know, we talked about this dampening of the circadian drive for sleep.
00:37:12.880
But it's a dampening for a whole bunch of things.
00:37:15.140
So the hormones underpinning urine production aren't as, you know,
00:37:19.480
urine production during the day, nothing at night.
00:37:24.560
So you're more likely to produce urine at night.
00:37:29.980
If you're sitting in a chair all day, then blood will tend to, you know,
00:37:35.420
you get your puffy ankles or your lower legs tend to fill with fluid, with blood.
00:37:41.580
And that blood is then integrated back into the body.
00:37:45.600
What's fascinating is that by just simply lying down and by sitting all day,
00:37:50.680
you can produce, you need to get rid of that fluid.
00:37:54.200
And so you can produce as much as a liter of urine
00:38:01.280
The other thing is that people who are on antihypertensives,
00:38:05.420
sometimes these hypertensives make you pee a lot.
00:38:09.220
They just try and get rid of blood volume to reduce blood pressure.
00:38:13.820
And so you have to be a little bit careful about those hypertensives,
00:38:18.620
The good news is that there are drugs that mimic the natural drugs that produce urine
00:38:29.140
which stops urine production when you're trying to sleep at night.
00:38:36.000
And many people sort of buy a little bottle that they can pee into by the bed
00:38:42.880
And in fact, as an aside, as I think I mentioned in the book,
00:38:45.700
those people that do pee into a bottle overnight,
00:38:48.760
they collect their urine because it's good for the garden.
00:38:52.840
You have to dilute it a bit if you're going to put it straight onto the soil.
00:38:56.240
But you can put it straight into your compost heap and it works a treat.
00:39:02.320
just try not to drink as much fluid before bed.
00:39:08.880
And, you know, that nighttime cup of tea or whatever,
00:39:11.840
just try and move it earlier and get it peed out before you actually go to bed.
00:39:16.840
So we've been talking about the circadian rhythm in sleep,
00:39:19.020
but circadian rhythm also governs our metabolism,
00:39:23.880
So tell us about that, the circadian rhythm in metabolism.
00:39:29.880
So what you've got is a nighttime metabolism and daytime metabolism.
00:39:34.660
So if we think about daytime, we are taking in calories.
00:39:38.880
And we're burning those calories as we take them in.
00:39:42.420
So daytime metabolism is completely different of nighttime metabolism,
00:39:54.680
And what's turning out to be fascinating is that
00:39:57.120
the way that we process food changes across the day.
00:40:01.160
So if you're taking glucose, you know, food in the morning and at lunchtime,
00:40:06.120
you're actually metabolizing that glucose very effectively.
00:40:09.680
But as you approach nighttime, you don't metabolize that glucose effectively.
00:40:15.020
And what happens is it gets turned to stored glucose either in the liver or laid down as fat.
00:40:20.980
And so it's very important to concentrate your food intake during the morning and at lunchtime
00:40:29.980
The problem is, of course, with changing work habits.
00:40:33.100
You know, in the old days, we used to live and work during the same space.
00:40:38.220
Now people may spend two hours getting to work and then coming back.
00:40:43.880
There's a sandwich, you know, over lunch, a quick sandwich over lunch.
00:40:47.520
And then finally you get home, you know, ravenously hungry, you stuff things into the microwave
00:40:52.700
and you're eating, you know, high fat, high sugar because that's what you're craving
00:40:56.500
because you haven't had, you know, calories during the day.
00:40:59.380
And, you know, you're hungry and you crave actually the worst kind of stuff.
00:41:03.520
But then you're calorie loading at the end of the day.
00:41:06.300
And it's much more likely to be laid down to fat
00:41:09.580
and predisposing to metabolic abnormalities and things like diabetes too,
00:41:14.520
which also raises some interesting issues about when we should exercise.
00:41:20.740
So if you exercise in the morning before breakfast,
00:41:25.180
you're still in the nighttime mode of metabolism where you're burning up stored calories.
00:41:31.100
The problem is that the power that you can exert for exercise
00:41:38.920
So a short, you know, 20-minute exercise bout can be really good at burning up
00:41:43.840
a few of the stored calories that you may not want.
00:41:47.320
But then later in the day when your core body temperature has risen
00:41:50.340
means that you can exercise for longer and with more power.
00:41:55.060
And so the calories that you've taken in during the day can be burnt up
00:41:58.620
more effectively by late afternoon, early evening exercise.
00:42:03.000
You don't want to exercise too late because that will raise core body temperature
00:42:07.140
and a higher core body temperature makes it more difficult to get off to sleep at night.
00:42:12.360
So the bottom line with metabolism and exercise is that try and concentrate your calories
00:42:17.900
during the first half of the day, breakfast and lunchtime, light evening meal.
00:42:23.600
An exercise first thing in the morning, short bout before breakfast,
00:42:27.540
burning up stored calories and a later more vigorous set of exercises
00:42:31.580
to burn up calories you've taken in during the day.
00:42:34.520
And you'll be able to exercise with greater vigor later in the day.
00:42:38.160
Yeah, that nutrition advice reminds you of that saying,
00:42:41.180
eat breakfast like a king, lunch like a prince, and dinner like a pauper.
00:42:46.520
And it really is what I think that's a couple of hundred,
00:42:50.320
maybe even a thousand years old advice, and it's still true today.
00:42:54.500
And it's worth bearing in mind how our eating habits have changed.
00:42:57.940
I mean, my grandparents, for example, my grandfather would come home for what they called dinner,
00:43:06.620
You know, it was a decent breakfast, classic English breakfast,
00:43:09.500
followed by a large lunch, and then a light tea.
00:43:12.900
And so we've changed because of our working habits when we take our calories in,
00:43:16.800
in, you know, sort of a hundred years, less than a hundred years.
00:43:20.200
I think I've noticed, done some observations with my own metabolism
00:43:25.740
I did this continuous glucose monitor a while back ago.
00:43:30.400
And one thing I noticed is if I ate a lot of carbs first thing in the morning,
00:43:34.060
like very first thing in the morning, my glucose spiked significantly.
00:43:37.540
But if I shifted things a little bit, if I took those carbs and like ate them a little bit later,
00:43:44.020
And I think it's because like my body was still waking up.
00:43:49.500
instead of having me first thing in the morning, did better for me.
00:43:51.520
Well, what's happening, of course, is that first thing in the morning,
00:43:56.280
And what cortisol does is prepare you for activity.
00:44:00.060
So it will release, you know, it rises naturally under the influence of a circadian rhythm.
00:44:04.680
And that will increase heart rate, increase glucose into the circulation.
00:44:08.720
So you do get a peak, a spike in the morning of glucose under the regular,
00:44:14.800
Is there anything, a lot of people have been talking about lately,
00:44:17.760
is that your caffeine consumption, like you should wait a little bit
00:44:21.820
before you have your coffee or tea in the morning.
00:44:28.720
I mean, personally, I drink coffee first thing in the morning.
00:44:37.620
then that morning coffee can be really helpful to increase alertness
00:44:45.340
is that you try not to drink it after two o'clock in the afternoon.
00:44:51.460
So coffee in the evening will actually keep me awake.
00:44:57.000
That's another observation I made as I shifted into midlife.
00:44:59.620
Before my 20s and 30s, I could have a caffeinated soda at dinnertime.
00:45:04.600
I could go to sleep like a baby at 10.30, 11 o'clock at night.
00:45:07.960
Now, if I have a caffeinated soda after 2 p.m., I can't sleep.
00:45:16.140
And, of course, it's the way we process caffeine.
00:45:18.540
I mean, the thing about caffeine, which is so interesting, of course,
00:45:21.060
is that we've talked about the circadian regulation of sleep.
00:45:25.860
But there's another timer, which is called the homeostatic driver for sleep
00:45:31.680
And it basically means the longer you've been awake,
00:45:34.200
the greater the need for sleep, the greater the sleep pressure.
00:45:36.840
And one of the substances that builds up while we're awake is adenosine.
00:45:45.800
Now, what happens is that caffeine blocks the receptors in the brain
00:45:53.220
because the body's signal saying we're tired is being blocked by caffeine.
00:46:00.800
you've done some research and highlighted research in this book
00:46:06.360
So how is our immune system influenced by our circadian rhythm?
00:46:10.560
The more we dig in, we're finding that so many really important systems
00:46:14.760
are being influenced by the circadian system, not least the immune system.
00:46:19.080
And so what was being discovered is that vaccination at different times
00:46:25.560
The classic study was on elderly individuals with the flu vaccine,
00:46:29.680
showing that if you have the flu vaccine in the morning,
00:46:32.700
it was three times more effective in generating an antibody response
00:46:39.740
And so we now know, and this fits beautifully with the idea that the immune system
00:46:43.660
is turned up during the day, and it is turned down whilst we're asleep at night.
00:46:52.020
Why would you not have the immune system on at full throttle all the time?
00:46:56.740
And the argument, we don't know, but the argument seems to be that
00:47:00.600
one of the great problems of having an immune system
00:47:06.080
where the immune system attacks the body, its body.
00:47:09.600
And so the thought is that you turn it up during the day
00:47:13.440
when you're moving around, meeting other people,
00:47:17.160
and you're more likely to encounter pathogens in the environment.
00:47:21.060
But you turn it down at night when you're not mobile
00:47:27.880
And by doing that, you're much less likely to trigger autoimmune responses.
00:47:32.700
We don't know that for sure, but that's the working hypothesis.
00:47:36.420
Does our circadian rhythm affect how medication is processed by the body?
00:47:45.820
And so you can get massive time of day effects.
00:47:49.440
So sort of pioneers from the States, Bill Horesky,
00:47:52.840
has shown that taking anti-cancer drugs at particular times,
00:47:56.580
classic studies he did on ovarian cancer with the same drug,
00:48:02.860
In ovarian cancer, after five years, one group survived.
00:48:06.440
45% of the group survived versus 10% in the other group.
00:48:10.540
And so the same drug, same concentration, different time,
00:48:16.520
Another study on kids with leukemia looking at chemotherapy showed that after about six and a
00:48:23.180
half years with the evening treatment of the cocktail of drugs, 75% were still alive,
00:48:30.520
whereas for the morning cocktail of drugs, it had dropped to 35%.
00:48:37.140
So lots of data in anti-cancer drugs, same for radiotherapy, incidentally, depends upon the drug
00:48:48.660
Another really interesting area is in one's high blood pressure and taking,
00:48:55.060
There's a dangerous window between 6am and 12 noon when there's a 50% greater chance
00:49:00.560
of having a stroke, for example, than any other time of the day.
00:49:03.980
So when do you take your antihypertensives that blunt that sharp rise in morning blood pressure?
00:49:09.880
Well, you know, without thinking about it, you might say, well, I take it in the morning.
00:49:13.420
But of course, the time you've got up, you've taken the drugs, and the time they've reached
00:49:17.760
the circulation, you're probably past that danger window, that spike.
00:49:22.400
And some studies from Spain showed that those individuals who took their antihypertensives
00:49:28.300
before bed had a 50% greater chance of survival over a 10-year period than those that took their
00:49:35.920
antihypertensives first, you know, when they woke up, which I think is really interesting.
00:49:40.240
And of course, that's based upon the fact that the antihypertensives hang around in the body.
00:49:46.300
So by taking them before you go to sleep, they'll be at a high level still in the morning when that
00:49:51.640
sharp rise in blood pressure occurs, which is one of the drivers for producing a stroke.
00:49:58.200
But as I say, if you take it after you've woken up, then the time the drug is actually
00:50:03.020
taken into the body, you're past that danger window.
00:50:06.380
Well, Russell, this has been a great conversation.
00:50:07.980
Is there some place people can go to learn more about the book and your work?
00:50:11.880
I mean, Lifetime is available in the United States, published by Yale University Press.
00:50:19.120
And most of the discussion that we've had is in Lifetime.
00:50:22.700
And also, if you're interested in our website, which I have to say, like most websites need a
00:50:27.640
bit of updating, you go to the Sleep and Circadian Neuroscience Institute, University of Oxford,
00:50:34.000
And also, if you do a Google for me, you'll see some podcasts and stuff online.
00:50:38.620
And if anybody's really interested and has specific questions, we can always sort of
00:50:45.220
I should say about Lifetime, one of the great things by working with Penguin is that they
00:50:50.100
didn't kick back about including citations, references.
00:50:54.320
So the science is accompanied by the scientific paper that supports that statement.
00:50:59.260
So it sounds really intimidating that there are 920 references in the book.
00:51:06.720
You know, members of the public have said, thank you so much for treating us as adults.
00:51:10.980
You know, if you want to dig deeper, the information is there.
00:51:14.720
And I had one very amusing email from a person who said, yes, I was telling my husband about,
00:51:19.980
in fact, it was when to take his hypertensives.
00:51:27.040
And he was convinced that he should change his behavior.
00:51:30.300
So I think what the book tries to do is provide the science and then people can make choices
00:51:34.980
based upon the science about what they want to do.
00:51:39.140
Part of the message in Lifetime is that one shoe size doesn't fit all.
00:51:44.520
And partly one of the reasons I wrote it was because I was absolutely fed up with sort of
00:51:49.240
the sergeant majors of sleep screaming, you must get eight hours.
00:51:56.880
Sleep is a highly dynamic, very flexible behavior.
00:52:00.380
And it's all about deciding whether you're getting the sleep that you need and using the
00:52:05.520
science to nudge you and advise you where you feel that things might need a change.
00:52:10.900
But it is absolutely not somebody screaming at you, you must do this and that.
00:52:19.980
And when you're coming out to the UK next, I hope we can get together.
00:52:27.620
It's available on Amazon.com and bookstores everywhere.
00:52:30.220
Check out our show notes at awim.is slash circadian, where you find links to resources.
00:52:35.160
Well, that wraps up another edition of the AOM podcast.
00:52:45.440
Make sure to check out our website at artofmanly.com where you find our podcast archives,
00:52:49.100
as well as thousands of articles that we've written over the years about pretty much anything
00:52:53.400
And if you haven't done this already, I'd appreciate it if you take one minute to give
00:52:59.820
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00:53:03.220
As always, thank you for the continued support.
00:53:05.680
Until next time, it's Brett McKay reminding you how to listen to AOM podcast, but put what