The Art of Manliness - Unlock Better Sleep and Health by Harnessing Your Circadian Rhythm

00:00:00.000 Brett McKay here, and welcome to another edition of the Art of Manliness podcast.

00:00:11.360 You probably know your body follows a circadian rhythm and probably think of it as primarily

00:00:15.740 regulating your sleep-wake cycle, which it certainly does.

00:00:18.960 But your body's internal clock also regulates many other physical, mental, and behavioral

00:00:23.380 changes that occur every 24 hours.

00:00:25.280 And working with your circadian rhythm, rather than against it, can boost your health and

00:00:29.780 happiness.

00:00:30.780 Here to unpack how to do so is Russell Foster, professor of circadian neuroscience and the

00:00:35.360 author of Lifetime, Your Body Clock and Its Essential Roles in Good Health and Sleep.

00:00:40.280 In the first part of our conversation, we discussed some science and background on circadian rhythm

00:00:44.200 and its connection to light exposure.

00:00:46.280 We then turned to the practical implications of having an internal clock, including whether

00:00:50.520 you need to worry about viewing blue light at night, the significant mental and physical

00:00:54.220 harms that can accrue from working the night shift, and what can be done to mitigate them,

00:00:58.200 what influences your chronotype, and whether you're a morning lark or night owl, whether

00:01:02.000 you should be concerned if you're waking up in the middle of the night, why you wake up

00:01:04.980 to pee in the night, the best times of day to exercise, and how the circadian rhythm can

00:01:09.260 influence when you should take medication.

00:01:11.520 After the show's over, check out our show notes at awim.is slash circadian.

00:01:24.220 All right, Russell Foster, welcome to the show.

00:01:31.640 I'm really delighted to join you, Brett.

00:01:33.280 So you have spent your career researching circadian rhythms, our internal clock that governs our

00:01:40.740 physiology and we'll learn about today, our mood and other things as well.

00:01:44.960 How did you get into this line of research?

00:01:47.340 Well, I didn't get into circadian rhythms to begin with.

00:01:49.960 I mean, I went to university thinking I would become a marine biologist because I loved animals,

00:01:54.860 I loved zoology, and I loved swimming.

00:01:56.640 So duh, you know, it's obvious I was into marine biology.

00:02:00.260 Then I discovered physiology in my second year at university and found that fascinating, and

00:02:06.500 particularly how photoreceptors, light sensors work.

00:02:11.880 And I became really obsessed with, first of all, the pineal photoreceptors of tadpoles.

00:02:18.100 And you can record from this third eye, light responses.

00:02:22.020 And in fact, when you dim the lights, it would trigger a swimming response.

00:02:26.420 And so I got into weird photoreceptors.

00:02:28.700 Then for my PhD, I was working on the photoreceptors in birds that measure day length,

00:02:34.380 and that triggers their reproductive responses. 0.99

00:02:36.880 So as the day lengths increase during spring, it triggers reproduction.

00:02:41.340 And I was, you know, fascinated about, well, what's detecting that light?

00:02:45.840 And how is it being measured?

00:02:47.100 How do they measure the length of light versus dark?

00:02:51.100 And that then got me into sort of the circadian field proper, which is what receptors in the

00:02:58.980 eye of mammals, creatures like you and I, are detecting the light-dark cycle for the regulation

00:03:04.880 of internal circadian rhythms.

00:03:06.420 And at that point, it was simply assumed, well, we knew it was the eye, but it was assumed that

00:03:11.800 it would be the visual cells.

00:03:13.060 And we should, I know we're going to talk about the weird photoreceptors in the eye later,

00:03:17.200 but really it was a passion for light-sensing systems that got me into clocks.

00:03:22.200 And then along the way, you became a sleep researcher too.

00:03:26.200 Well, yeah.

00:03:27.060 And that was fascinating because I was working at Charing Cross Hospital at that point as part

00:03:33.160 of Imperial College in London.

00:03:34.720 And I was in an elevator with a psychiatrist and he said, oh, you know, you work on sleep,

00:03:40.520 don't you?

00:03:40.840 And I said, well, yeah, kind of.

00:03:43.300 And he said, well, my patients with schizophrenia have terrible sleep.

00:03:47.300 That's because they don't have a job.

00:03:49.480 So they go to bed late, get up late, miss my clinic and don't have friends. 0.99

00:03:53.180 And I thought that was one of the most stupid things I'd heard, but it triggered an interest 0.98

00:03:58.980 in, well, what is going on with those individuals? 0.99

00:04:02.280 So hooked up with another psychiatrist and we looked at her subjects, her patients with

00:04:08.780 a diagnosis of schizophrenia.

00:04:10.040 And we measured really for the first time their sleep-wake profiles.

00:04:13.680 And what became really extraordinary for me is that their sleep-wake patterns were absolutely

00:04:19.360 smashed.

00:04:20.020 And so I sort of then moved into humans and sleep research, combining both a knowledge

00:04:27.440 of circadian rhythms, these internal 24-hour body clocks, and how circadian rhythms in turn

00:04:34.160 regulate our 24-hour sleep-wake cycle.

00:04:37.420 Well, let's talk about the circadian rhythm in our internal clock.

00:04:41.040 So scientists have noticed for millennia that humans and other animals have a bodily schedule.

00:04:46.420 We want to wake up at a certain time and go to sleep at a certain time.

00:04:49.340 And for most of that time, they thought it was just light that was driving that.

00:04:54.840 And it is.

00:04:55.160 We're going to talk about that, your research in photoreceptors.

00:04:57.640 But then scientists discovered that we have an internal clock that ticks independently of

00:05:04.380 external cues.

00:05:05.560 How did scientists discover this internal clock?

00:05:09.240 Well, with all good biology, it started with good observation.

00:05:12.940 And back in 1729, I think it was, there was a French sort of scientist and de Marien, and

00:05:21.380 he was studying the movements of leaves of a plant called mimosa.

00:05:26.320 Many of your listeners may be aware of this plant because it's that plant where you touch

00:05:29.680 the leaves, they close up.

00:05:31.700 And what happens with those mimosa, and they really, it's really worth having one of these 0.85

00:05:35.420 in the house, is that you see that the plants' leaves open during the day and they close at

00:05:40.020 night.

00:05:40.580 And of course, the assumption was this is driven by the changing light levels.

00:05:45.360 And so what de Marien did was put these plants in a light tight cupboard and then sort of would

00:05:51.280 peek in at different times and see what the leaves are doing.

00:05:54.320 And to his astonishment, the leaves continue with this opening and closing movement under

00:06:00.080 conditions of complete darkness.

00:06:02.580 And that's one of the key criteria of identifying a circadian rhythm, something that persists with

00:06:08.900 a rhythm of about 24 hours under constant conditions.

00:06:13.060 Now, those early experiments by de Marien had a potential flaw in that he controlled for light,

00:06:19.260 but he hadn't controlled for temperature.

00:06:22.460 So Candol, about 100 years later, took these mimosa plants down to a salt mine.

00:06:28.060 Constant darkness and critically constant temperature.

00:06:32.180 And observed again, these opening and closing of leaf movement.

00:06:36.980 And so this was the first, and it was in plants, not in animals, where circadian rhythms were first

00:06:42.320 sort of observed quantitatively rather than just sort of anecdotally.

00:06:47.040 And then when did we discover this in humans?

00:06:48.460 How did they discover that humans had this similar thing?

00:06:51.700 Well, I suppose one of the first experiments, analogous to those plant experiments, was in Mammoth

00:06:56.700 Cave in Kentucky, where two researchers went down.

00:07:00.560 And this is in 1938-39.

00:07:03.740 And they showed that sleep-wake cycles would continue under conditions of constant darkness

00:07:11.980 and constant temperature.

00:07:13.800 But then work stopped, really, during the Second World War.

00:07:16.620 But after that, a chap called Ashoff in Germany built some bunkers where you could control light

00:07:23.680 and temperature exquisitely.

00:07:26.240 And then started to systematically, in the 1960s and 70s, study human rhythmicity under broadly

00:07:33.260 constant conditions.

00:07:34.480 Okay, so we have an internal clock that keeps us to a roughly 24-hour schedule.

00:07:39.960 And that clock works even if we're cut off from external stimuli.

00:07:43.100 So if you put yourself in a temperature-controlled, light-controlled room, your body will stay

00:07:48.240 on a 24-hour cycle.

00:07:50.260 But without external stimuli, it's not going to match the day-night cycle.

00:07:55.040 It's going to start to drift.

00:07:56.400 So for our circadian rhythm to line up with that day-night cycle, this is called entrainment,

00:08:00.980 it needs external stimuli, the most important of which is light exposure.

00:08:04.900 So what role does light play in our circadian rhythm?

00:08:08.180 Yeah, I think it's probably good just to step back a bit and sort of think about what our

00:08:14.440 biology needs to do.

00:08:15.960 And what we need to do is deliver the right stuff at the right concentration to the right

00:08:20.280 tissues and organs at the right time of the day.

00:08:22.940 And it's the circadian system that gives this time structure for life.

00:08:27.560 But it's no good having a clock ticking away, fine-tuning our biology to the varied demands

00:08:33.320 of the rest activity in the light-dark cycle, unless it's actually entrained or locked onto

00:08:38.680 that light-dark cycle.

00:08:39.720 And the most powerful signal is the dawn-dusk cycle.

00:08:45.280 And this is where I sort of got into circadian rhythms, because I was fascinated.

00:08:49.900 We knew that in the mammals that the receptor was in the eye, because if you have no eyes

00:08:55.820 as a result of a terrible accident, then your sleep-wake cycle, you get up later and later

00:09:01.100 and later each day, you're drifting through time.

00:09:03.680 So it's by an average, let's say, of 10 to 15 minutes each day, you're getting up later.

00:09:08.740 Or if you are in complete darkness, you again show that drift.

00:09:12.780 And it's due to the eyes.

00:09:15.220 But the thing that puzzled me is that how can it be that the visual cells, the rods and the

00:09:21.000 cones, can also be used for circadian light detection?

00:09:25.140 What I mean by that is what a visual cell has to do is grab light in a fraction of a second

00:09:29.920 and forget it's seen that light to give you a crisp image of our world.

00:09:34.720 What the circadian system needs is an overall impression of the amount of light at dawn and

00:09:41.540 dusk.

00:09:42.260 And this can be gathering light information over minutes and sometimes hours.

00:09:46.720 And I couldn't see how visual cells could provide that time-of-day information.

00:09:52.440 So we started working on mice with hereditary retinal disorders where the rods and the cones

00:09:59.940 had broken down as a result of gene defects.

00:10:03.500 So these animals were visually blind.

00:10:05.500 They had their eyes, but they were visually blind.

00:10:08.000 And so we decided to put them in running wheels, you know, a little running wheel in the cage

00:10:11.660 and monitored when they would start their activity and end their activity under a light-dark cycle.

00:10:16.840 And to our astonishment, these mice could regulate their circadian rhythms.

00:10:23.180 Not only could they do it, but they did it with the same sensitivity as those mice with

00:10:28.860 their rods and cones.

00:10:30.220 So there was something else in the eye because if you covered the eyes up, this response to

00:10:35.180 light would cease and the mice would start to drift through time.

00:10:39.480 And so this then led to the hunt for what this third receptor might be.

00:10:44.100 And we were able to show this in mice and Dennis Dacey was able to show this in monkeys and

00:10:50.180 others were able to show it in other groups of animals, that there's this third receptor

00:10:54.920 in the eye, which we've called photosensitive retinal ganglion cells.

00:10:59.260 And what they are is that there are multiple layers within the retina, that part of the eye,

00:11:05.160 where the rods and cones are contained.

00:11:06.820 And beneath the rods and cones, there's the inner retina, which does some processing of the

00:11:11.080 light signal.

00:11:11.660 And then they send that information to the ganglion cells.

00:11:15.080 And the ganglion cells have these long axons, which project from the eye into the brain to

00:11:20.380 form the optic nerve.

00:11:21.960 And what turned out to be, and it's still, I think it's still extraordinary, is that these,

00:11:26.980 there's 1% or so, depends on the species, but certainly a small number of those ganglion

00:11:32.760 cells are directly light sensitive using a blue light sensitive photopigment called melanopsin

00:11:39.580 or OPN4.

00:11:41.180 And so, yeah, the eye is not only the organ of space, because it provides us with our sense

00:11:47.140 of vision, but it's also, in a sense, the organ of time, because it can coordinate the

00:11:52.640 external light dark cycle with the internal day and make sure that everything is synchronized.

00:11:58.280 So we're doing the right thing at the right time.

00:12:01.200 Okay.

00:12:01.300 So the big takeaway there is there's a third receptor, photon receptor in our eye, not

00:12:07.020 just cones and rods.

00:12:08.300 Exactly.

00:12:08.660 So you could be blind and still be synced up with the dong dust cycle. 0.67

00:12:15.680 Absolutely.

00:12:16.320 And we were able to show that.

00:12:17.580 So we, I was in a seminar and an ophthalmologist was talking about his studies on an elderly

00:12:23.540 lady who had no apparent rods and cones as they were able to detect. 1.00

00:12:28.500 And so I said to him, you know, in the question time, well, what's her sleep wake cycle like?

00:12:33.320 Does she sleep and wake normally?

00:12:35.500 And he said, well, I don't know.

00:12:37.040 I'm an ophthalmologist.

00:12:38.260 Why would I ask something like that?

00:12:40.320 So anyway, we worked with this ophthalmologist and discovered that this lady with no conscious 0.98

00:12:45.600 light perception was still able to regulate her rest activity cycles perfectly normally.

00:12:51.520 It's really quite extraordinary.

00:12:53.400 And so, and we were able to work out that it was those photosensitive retinal ganglion

00:12:57.980 cells.

00:12:58.440 We were also able to show in that individual that these new photoreceptors do more than

00:13:03.020 just regulate the clock.

00:13:04.140 They seem to provide a generalized measure of environmental brightness to, for example,

00:13:10.000 the pupil.

00:13:10.500 Part of our pupil constriction is actually being regulated by those photosensitive

00:13:15.580 retinal ganglion cells.

00:13:17.320 We also asked this lady if she had any conscious detection of light.

00:13:22.540 And she said, absolutely none.

00:13:24.280 But Dennis Stacy had shown that these PRGCs in a monkey project to some of the visual

00:13:29.560 structures in the brain.

00:13:30.900 So we thought, well, maybe she's got some subconscious ability to detect light. 0.99

00:13:36.260 And anyway, we did some studies with her.

00:13:38.560 And yeah, absolutely.

00:13:40.420 When we turn the lights on and then off for a period, and we asked her whether the lights

00:13:45.000 on or off, she could always tell when the lights were on and off, even though she had

00:13:49.120 no conscious awareness of light.

00:13:51.880 So really that and more studies in mice have shown that these receptors do a heck of a lot

00:13:57.260 of brightness detecting tasks, including regulating levels of alertness, even heart rate in some

00:14:03.740 circumstances.

00:14:05.060 And indeed, it looks as though they're contributing to mood.

00:14:08.080 So increase levels of light, you can increase alertness, and you can also alter mood.

00:14:13.300 So yeah, it's turned out to be something quite extraordinary.

00:14:16.800 How can the timing of our light exposure influence our circadian rhythms?

00:14:20.840 That is, if we got exposed to light earlier in the day, will that affect our circadian rhythm

00:14:25.360 overall?

00:14:26.480 Well, that's a really key point, Brett, because morning light advances the clock.

00:14:31.400 It makes us get up earlier and go to bed earlier.

00:14:34.820 Dusk light delays the clock.

00:14:36.880 We go to bed later and get up later.

00:14:38.840 Now that's important because light during the middle of the day is not having too much

00:14:42.520 of an effect.

00:14:43.080 And we've shown in university students around the world that those who are owls, they have 1.00

00:14:49.040 a late chronotype.

00:14:50.600 They like to go to bed late and get up late.

00:14:52.880 And we can talk more about chronotype later.

00:14:55.240 They were missing morning light, which would advance the clock, but they were getting the

00:14:59.840 late afternoon, early evening light, which would shift them to a later time.

00:15:04.780 So when you see light can be incredibly important in influencing whether you want to get up late

00:15:11.060 or go to bed early.

00:15:12.220 What if you see light at both times?

00:15:14.660 Like I wake up, I wake up early and I'm exposed to light during my morning walk.

00:15:18.300 And then I, sometimes I'm out at dusk and getting light exposure there.

00:15:22.900 What does that just kind of balance things out?

00:15:24.700 Exactly.

00:15:25.360 And in fact, when we were all agricultural workers and, you know, up until 1800, more than

00:15:30.340 90% of the population were agricultural workers getting symmetrical dawn-dusk exposure.

00:15:36.880 And so we stayed beautifully on cue, rose with the sun and went to bed with dusk.

00:15:41.460 And in fact, artificial light was really expensive up until the 20th century.

00:15:47.520 I mean, in the 19th century, a candle, which actually isn't very bright and wouldn't have

00:15:52.360 had much effect on the clock, was the cost of a working man's daily wage.

00:15:55.960 And so people just synchronize their biology with the dawn-dusk cycle quite naturally.

00:16:03.860 So lately, there's been a lot of talk about how viewing blue light from our digital devices before

00:16:09.080 bed can disrupt our circadian rhythm.

00:16:10.900 So people say, well, you should avoid that.

00:16:13.940 Or if you're going to use it, turn your screen yellow.

00:16:16.200 You wear these orange glasses.

00:16:18.020 Is there anything to that idea?

00:16:19.400 No, in short.

00:16:22.360 I mean, this is a rapidly moving field, but what's happened in the past few years.

00:16:27.120 So the early studies looking, for example, at a Kindle, and people were asked to look at

00:16:32.740 a Kindle on its brightest light setting for four hours on five consecutive nights.

00:16:38.400 And that delayed sleep onset just statistically significantly by nine minutes.

00:16:43.240 So a small effect there.

00:16:45.400 But it did have an effect upon the rhythms of melatonin.

00:16:49.360 And so this sort of got into the literature and the press as, oh, well, reading a Kindle

00:16:54.840 before you go to bed is a disaster for your circadian rhythms.

00:16:57.940 And of course, it had a tiny effect on sleep-wake.

00:17:01.580 And then the experiments were repeated.

00:17:04.060 And instead of people being kept under dim light before the evening Kindle use, they gave

00:17:11.780 them bright light, about six hours of bright light, say about 500 lux during the day.

00:17:16.960 And that bright light exposure completely abolished any subtle effects of light in the evening.

00:17:22.740 So we've got to be really careful.

00:17:24.640 These are great experiments that were done, the initial ones on the Kindle, but they were

00:17:29.280 lab-based experiments.

00:17:30.520 They didn't take into account the real-world situation.

00:17:34.120 And if you're getting moderate levels of light during the day, you're not going to be sensitive

00:17:38.120 to dim light or so sensitive to dim light in the evening.

00:17:41.200 So that was one of the studies that has been overturned.

00:17:44.720 There's been recent reviews looking at the use of yellow-blue-blocking glasses on behavior,

00:17:51.100 and there's no effect of that.

00:17:53.520 And indeed, these screens that shift from blue-enriched light to red-enriched light,

00:17:58.700 the efflux computer programs, have also been shown to have no effect upon circadian biology

00:18:04.740 at all.

00:18:05.740 So it's one of those things where, you know, we discovered that these photosensitive retinal

00:18:09.820 ganglion cells are maximally sensitive to blue light.

00:18:12.540 And people have said, ah, well, it'll be blue light that will be important for disrupting

00:18:17.840 these receptors and the circadian system in the evening.

00:18:20.960 But the key thing that's not really appreciated is that these receptors need quite a bit of

00:18:27.780 light for a long period of time.

00:18:29.940 And the impact of that light will depend upon how much light you've seen during the day,

00:18:35.100 how old you are, the angle of gaze.

00:18:37.960 And so it's turning out to be a very complicated signal that's being integrated by those receptors

00:18:44.540 and then by the suprachiasmatic nuclei.

00:18:47.380 Bottom line is, we don't have any strong evidence that blue light, as sort of the levels that you

00:18:52.720 get from computer screens and all the rest of it, will actually disrupt your sleep in the evening.

00:18:57.200 Now, of course, if it's brighter, it will.

00:19:00.100 But remember, these receptors need bright light for a long period of time.

00:19:03.220 That's the other thing about the experiments in the lab.

00:19:06.080 They've looked at not just a small exposure, a short duration exposure, but people have

00:19:11.460 been given six or seven hours of light exposure.

00:19:14.680 And you need those long effects with dim light to get any sort of shift in the circadian system.

00:19:20.360 So what the circadian system is doing is integrating light over long periods of time to get an effect.

00:19:26.220 Okay, so you can throw away your yellow-orange glasses.

00:19:30.520 Well, I would.

00:19:31.440 I mean, I just think it's, yeah, and there's a whole industry that's sort of built around that sort of stuff.

00:19:36.020 Yeah.

00:19:36.280 What about just exposure to artificial light in the home at nighttime?

00:19:40.340 Does that affect your circadian rhythm?

00:19:41.740 This is a really interesting question.

00:19:45.340 And again, we don't fully know because the experiments have been extrapolated from lab experiments where

00:19:51.360 people have been kept under relatively dim light and then exposed to dim light in the evening.

00:19:57.100 And they've been exposed to durations of light for six, seven hours.

00:20:01.860 Whether that can map on to the real world, we don't know.

00:20:04.760 But there are estimates suggesting that, you know, about 100 lux, which is not very much light,

00:20:12.200 with six and a half hours of exposure, can have a bit of an effect upon the clock.

00:20:16.620 But that will vary enormously.

00:20:18.240 Some studies from Australia have shown that the sensitivity of the clock between individuals

00:20:23.180 can vary hugely.

00:20:25.000 And that's independent of age.

00:20:26.600 And we know that the clock is getting less sensitive as we age.

00:20:29.660 So there's lots of factors going on here.

00:20:31.880 And at the moment, we don't have the evidence base for hard recommendations about light exposure

00:20:39.100 in the evenings.

00:20:39.900 It makes sense not to get bright light exposure in the evening because that will delay the clock.

00:20:46.940 But how bright that light should be and for how long and for what color or wavelength,

00:20:52.980 we don't fully appreciate it.

00:20:54.980 So, you know, rule of thumb, minimize light exposure, you know, in the evenings.

00:20:59.420 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.

00:21:12.920 So it makes it harder to go to sleep.

00:21:14.500 Absolutely.

00:21:15.100 It's an alerting effect.

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

00:21:25.040 and perhaps stress levels.

00:21:26.040 And that will undoubtedly delay your sleep onset.

00:21:29.440 So that's the problem with, you know, with social media and why I think most of us would

00:21:33.980 recommend not using these smartphone devices or stuff like that before you go to bed, because

00:21:39.520 it'll increase levels of alertness.

00:21:41.300 Now, of course, you can use a Kindle for your relaxing book, your few pages of Jane Austen or

00:21:46.360 whatever it is that relaxes you and gets you off to sleep.

00:21:49.160 That's not a worry, but it's the sort of interactive stuff and the stress that you get from work emails

00:21:54.620 and all the rest of it.

00:21:55.780 All right.

00:21:55.860 That's really interesting.

00:21:57.120 We're going to take a quick break for your word from our sponsors.

00:22:01.100 And now back to the show.

00:22:02.860 What happens when we unsync our bodies from the usual wake during the day and asleep during

00:22:08.320 the night schedule?

00:22:09.040 Like what if you're a shift worker?

00:22:10.180 What goes on?

00:22:11.260 What happens?

00:22:11.560 Well, I think this is such an important issue.

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.

00:22:29.560 So fluctuations in mood, irritability, anxiety, loss of empathy.

00:22:34.800 What's so fascinating that the tired brain is not good at picking up the sort of social signals

00:22:39.980 for other individuals and reading what their moods and their emotions are like.

00:22:44.360 High levels of frustration.

00:22:46.200 I think another fascinating one is risk-taking and impulsivity. 0.99

00:22:50.200 We're much more likely to do stupid and unreflective things. 0.95

00:22:54.320 Yeah, I'm sure I can go through that traffic light before it goes red, for example. 0.98

00:22:59.380 Negative salience.

00:23:00.440 Some very interesting studies from Germany have shown that the tired brain remembers negative

00:23:05.700 experiences but forgets the positive ones.

00:23:08.060 So tired people, you know, their whole worldview is being influenced by the stuff that they

00:23:13.940 remember, which is invariably negative.

00:23:16.460 You're also much more likely to use caffeine to drive you through the waking day and then

00:23:22.620 try and reverse the effects of caffeine with sedatives, such as alcohol or sleeping tablets,

00:23:28.700 both of which do not provide a biological mimic for sleep.

00:23:32.220 They sedate you.

00:23:33.340 They don't, you know, actually help you get to sleep.

00:23:36.020 So that's some of the emotional responses, cognitive responses.

00:23:40.520 So our whole ability to function, to come up with novel solutions to complex problems

00:23:45.720 is impaired by lack of sleep.

00:23:47.580 Our ability to multitask.

00:23:49.680 So to extract from all the bits of information that we're being bombarded with constantly,

00:23:54.200 what's relevant and what we should ignore.

00:23:56.280 So multitasking falls apart, memory consolidation, information processing, concentration, decision

00:24:02.380 making, all those sorts of attributes that make us such a special productive creature

00:24:08.260 are lost with a tired brain.

00:24:11.460 And then if we move on to the sort of impact on physiology and health after years of night

00:24:18.000 shift work.

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.

00:24:35.780 You're pumping harder.

00:24:37.660 Your heart is pumping harder.

00:24:38.940 You're releasing more glucose into the circulation.

00:24:41.500 So that's going to have metabolic problems, you know, increasing levels of blood glucose,

00:24:46.020 predisposing to type 2 diabetes, lowered immunity.

00:24:49.360 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

00:24:59.460 indeed infection in night shift workers.

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 0.77

00:25:21.600 cancer.

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.

00:25:39.280 And there are even data emerging now.

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

00:25:47.520 when you're much older.

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

00:25:57.080 clearance system within the brain.

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

00:26:24.100 to predispose you to dementia.

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

00:26:34.380 direction.

00:26:35.360 All right.

00:26:35.460 So shift work sounds like it's terrible for you.

00:26:38.240 Yeah.

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. 1.00

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

00:26:55.320 can't do shift work.

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

00:27:34.600 falling asleep.

00:27:35.220 And of course, you know, high end cars now have this technology built in loss of vigilance

00:27:40.280 and tiredness in the workspace.

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

00:27:55.020 physical and mental health.

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?

00:28:04.680 And I think that's, you know, early detection.

00:28:06.860 We see obesity, type 2 diabetes, metabolic abnormalities in night shift workers.

00:28:12.160 What's the food that's available?

00:28:13.720 Well, it's as bad as it could possibly be.

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

00:28:40.080 to day shift workers.

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.

00:28:56.540 So there's stuff that we can do.

00:28:58.680 And, you know, just to finish on that, this section is that we know that these pathologies get

00:29:02.960 worse with time.

00:29:04.380 So should we think about limiting night shift work to three to four years on, and then maybe

00:29:10.040 three to four years off?

00:29:11.240 I don't have the data to support that suggestion, but I think it's something we should be looking

00:29:15.480 at.

00:29:16.060 The problem, of course, is that most people don't want to do night shift work, but they

00:29:19.620 have to because of economic circumstances.

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

00:29:40.060 earlier or later.

00:29:42.020 What causes those differences?

00:29:44.720 Yeah.

00:29:45.080 There's three basic components to one's chronotype.

00:29:48.420 One is our genetics.

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.

00:29:58.460 So there's a genetic element.

00:30:00.620 The second is how old you are.

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,

00:30:15.220 more owl-like chronotype.

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

00:30:44.880 and then decline slowly as you age.

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.

00:30:59.280 So it's a two-hour, it's a big effect.

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

00:31:12.540 clock, makes you go to bed later.

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

00:31:52.180 light, but not the morning light.

00:31:54.400 And so getting up on the Monday is much more tricky for somebody who's oversleeping at the

00:31:58.840 weekend to try and catch up on their sleep.

00:32:00.780 But chronotype is really important.

00:32:02.840 Genetic component, it's got an age component.

00:32:06.220 And the third component is when you see light.

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

00:32:17.940 you those shortened night experiences.

00:32:20.360 I want to dig more into how our understanding of circadian rhythm can help us improve our

00:32:23.900 sleep.

00:32:24.200 Because I've been experiencing this this year.

00:32:25.960 So I turned, I'm turning 42 this year.

00:32:28.440 And starting at the beginning of this year, my sleep just started changing.

00:32:33.180 It was really weird.

00:32:33.840 For the longest time, I could go to bed about 1030 and wake up about seven, never wake up

00:32:39.000 in the middle of the night.

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.

00:32:46.740 I was like, what is going on here?

00:32:48.420 So what is going on?

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.

00:32:57.380 First of all, you're in your 40s.

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.

00:33:05.440 But, you know, it's job, career, procession.

00:33:08.000 It's partnerships.

00:33:09.000 It's relationships.

00:33:10.540 It may be kids.

00:33:11.500 It may be family.

00:33:12.460 All of those sorts of things tend to crash in on you in your 40s and provide, you know,

00:33:17.940 added levels of stress and anxiety.

00:33:19.760 Which means if you wake up, you'll sort of be flooded with all of these thoughts and it's

00:33:24.340 more difficult to get back to sleep.

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

00:33:53.180 sleep again.

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.

00:34:04.020 So, a 12-hour light-dark cycle.

00:34:06.340 And they flipped to being bimodal in sleep. 0.97

00:34:09.660 They fragmented their sleep.

00:34:11.040 So, it's nothing to worry about if you wake up during the night.

00:34:15.000 It's normal.

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

00:34:44.740 and get back to sleep.

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.

00:34:53.340 They have a stress or an anxiety issue.

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

00:35:07.460 to get back to sleep.

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

00:35:33.360 we had earlier in our earlier life.

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

00:35:44.360 had when we were 30.

00:35:45.620 Okay, I like that.

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

00:35:57.900 sleep.

00:35:58.100 It's just like, wow.

00:35:59.020 So, I've just got to get used to it.

00:36:00.480 It's fine.

00:36:01.040 Well, that's it.

00:36:01.580 Yeah, and not get punctured by it.

00:36:02.780 And I think you've raised a really important point because, you know, how do we know if we're

00:36:06.300 getting enough sleep?

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?

00:36:15.320 You know, how's your sleep pattern changed?

00:36:17.740 Do you need an alarm clock or somebody else to get you out of bed?

00:36:20.740 Does it take you a long time to wake up?

00:36:23.020 Are you feeling groggy, for example?

00:36:25.280 And do you feel sleepy and irritable when you're awake?

00:36:28.500 Do you crave a nap?

00:36:30.180 Is your, we touched on this, is your behavior overly impulsive?

00:36:34.100 And do you crave caffeinated drinks?

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.

00:36:44.240 You don't have the same empathy. 1.00

00:36:45.660 You seem to be doing stupid and unreflected things. 1.00

00:36:48.700 This is all telling us we're not getting the sleep we need. 1.00

00:36:50.880 And we do need to listen to others.

00:36:52.800 I think there's a tendency to be a little bit defensive about our sleep.

00:36:56.400 And I think actually, it's great.

00:36:58.260 You know, if people are saying these things, it's important.

00:37:00.520 We should listen.

00:37:01.940 What about, you talk about this in the book, peeing in the middle of the night,

00:37:05.060 having to wake up and go pee.

00:37:06.300 What's going on there?

00:37:07.200 Well, there's lots of interesting stuff there.

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.

00:37:22.300 Well, that kind of gets a bit sloppy.

00:37:24.560 So you're more likely to produce urine at night.

00:37:28.500 And there's two other factors here.

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.

00:37:40.100 And then you lie down.

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. 0.86

00:37:54.200 And so you can produce as much as a liter of urine

00:37:57.440 simply by lying down after a day of sitting.

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,

00:38:17.260 which can make urine production worse.

00:38:18.620 The good news is that there are drugs that mimic the natural drugs that produce urine

00:38:25.060 at particular times.

00:38:26.600 And you can take those vasopressin,

00:38:29.140 which stops urine production when you're trying to sleep at night.

00:38:32.780 So, yeah, it's a common problem.

00:38:34.780 You know, many people do it.

00:38:36.000 And many people sort of buy a little bottle that they can pee into by the bed

00:38:39.540 so they don't have to go to the loo.

00:38:41.200 I mean, you know, there's lots of strategies.

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.

00:39:00.020 I imagine also if you want to avoid it,

00:39:02.320 just try not to drink as much fluid before bed.

00:39:04.820 Yeah, well, absolutely.

00:39:05.740 Yeah, absolutely.

00:39:06.780 I mean, these are the sort of tricks.

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,

00:39:21.840 how our body uses energy.

00:39:23.880 So tell us about that, the circadian rhythm in metabolism.

00:39:27.560 Yeah, this is a really interesting area.

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,

00:39:45.440 which is we don't feed, we don't eat at night.

00:39:48.820 We're mobilizing stored calories.

00:39:51.560 So they're very different metabolic states.

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

00:40:27.900 rather than late into the evening.

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.

00:40:42.080 There's no time for a breakfast.

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.

00:41:18.420 So there's a couple of strategies here.

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

00:41:35.540 isn't as great first thing in the morning.

00:41:37.600 It rises throughout the day.

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.

00:42:45.360 Yeah, yeah, absolutely.

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,

00:43:03.740 which was lunchtime.

00:43:04.960 And that was the main meal of the day.

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

00:43:23.580 and how it's connected to my circadian rhythm.

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,

00:43:42.280 it wasn't as high.

00:43:43.420 It was blunt.

00:43:44.020 And I think it's because like my body was still waking up.

00:43:47.180 So shifting my carbs later in the morning,

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,

00:43:54.280 you've got a spike in cortisol.

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,

00:44:13.300 probably being driven by cortisol.

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.

00:44:24.260 Anything to that?

00:44:25.900 Well, I don't have any data to hand, really.

00:44:28.720 I mean, personally, I drink coffee first thing in the morning.

00:44:32.020 I find it useful to wake me up a bit.

00:44:34.840 And particularly, I think if people are tired,

00:44:37.620 then that morning coffee can be really helpful to increase alertness

00:44:40.900 during the morning commute, for example.

00:44:42.620 But I think the key thing about coffee for me

00:44:45.340 is that you try not to drink it after two o'clock in the afternoon.

00:44:49.500 I am really sensitive to coffee.

00:44:51.460 So coffee in the evening will actually keep me awake.

00:44:54.800 So I try and cut it out earlier.

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.

00:45:03.920 No problem.

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.

00:45:12.620 I have a hard time falling asleep.

00:45:13.760 That's interesting.

00:45:14.580 Yeah, and it's one of those things of aging.

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

00:45:30.740 or sleep pressure.

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.

00:45:42.560 And adenosine is a signal for sleepiness.

00:45:45.800 Now, what happens is that caffeine blocks the receptors in the brain

00:45:49.540 that respond to adenosine.

00:45:51.000 That's why we feel genuinely more alert,

00:45:53.220 because the body's signal saying we're tired is being blocked by caffeine.

00:45:58.660 That's interesting.

00:45:59.540 The last thing I want to talk about,

00:46:00.800 you've done some research and highlighted research in this book

00:46:03.000 about our circadian rhythm and immune system.

00:46:06.360 So how is our immune system influenced by our circadian rhythm?

00:46:09.140 This is so fascinating.

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

00:46:24.400 was having different effects.

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

00:46:36.940 than if you took it in the late afternoon.

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.

00:46:50.260 And you could ask, well, why?

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

00:47:03.400 is that you can get autoimmune responses,

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,

00:47:16.260 and you're in the environment,

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

00:47:24.980 and far less likely to encounter pathogens.

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?

00:47:42.320 Oh, yes.

00:47:43.220 Huge impact.

00:47:44.340 I mean, it really is extraordinary.

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,

00:48:00.720 but given at different times.

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,

00:48:13.400 massive impact upon long-term survival.

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%.

00:48:34.920 Same drug, same concentration, different time.

00:48:37.140 So lots of data in anti-cancer drugs, same for radiotherapy, incidentally, depends upon the drug

00:48:44.160 and it depends upon the treatment.

00:48:45.640 So there's no one rule fits all there.

00:48:48.660 Another really interesting area is in one's high blood pressure and taking,

00:48:53.040 when do you take antihypertensives?

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.

00:49:44.760 They have a short half-life.

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?

00:50:11.320 Yeah.

00:50:11.880 I mean, Lifetime is available in the United States, published by Yale University Press.

00:50:16.640 UK, it's by Penguin.

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,

00:50:32.840 and you'll find us.

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

00:50:43.100 ping you the papers that you're interested in.

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.

00:51:04.120 But that, it's turned out to be fantastic.

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.

00:51:21.940 And he said, oh, that's complete nonsense.

00:51:23.940 And she said, go to the reference in the book.

00:51:26.200 He did.

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.

00:51:38.000 And I should just finish.

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.

00:51:53.200 You shouldn't look at a Kindle.

00:51:54.580 You can't do this.

00:51:55.500 You can't do that.

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.

00:52:15.660 Well, Russell Foster, thanks for your time.

00:52:16.840 It's been a pleasure.

00:52:18.000 Well, absolutely.

00:52:18.900 Great to chat, Brett.

00:52:19.980 And when you're coming out to the UK next, I hope we can get together.

00:52:23.560 Sounds great.

00:52:24.900 My guest today was Russell Foster.

00:52:26.080 He's the author of the book Lifetime.

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.

00:52:33.980 We delve deeper into this topic.

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

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00:52:57.260 It helps out a lot.

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00:52:59.820 Please consider sharing the show with a friend or family member who would think there's

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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

00:53:09.540 you've heard into action.

The Art of Manliness - August 21, 2024

Unlock Better Sleep and Health by Harnessing Your Circadian Rhythm

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