I’m excited to have Dan Pardi as a guest on today’s show. I met Dan at PaleoFX last March, and we instantly hit it off. As a PhD candidate sleep researcher at the University of Leiden in the Netherlands, and the CEO of Dan’s Plan, Dan is one of the most knowledgable people on the effects of sleep on health I’ve come across. I hope you enjoy the interview!
In this episode, we cover:
6:48 Why sleep is essential to health
20:30 The telltale signs of sleep deprivation
32:40 Does light play a role in getting better sleep?
40:28 The truth about polyphasic sleep
49:00 Simple tips for getting better quality sleep
Full Text Transcript:
Steve Wright: Hi, and welcome to another episode of the Revolution Health Radio Show brought to you by ChrisKresser.com. I’m your host, Steve Wright from SCDLifestyle.com, and with me is integrative medical practitioner, licensed acupuncturist, and healthy skeptic, Chris Kresser. How’s it going?
Chris Kresser: I’m doing pretty well, Steve. How are you?
Steve Wright: I’m pretty jacked tonight. We have a very special guest on the line.
Chris Kresser: Yeah, I’m excited to introduce Dan Pardi. Dan and I met at Paleo f(x). Actually we had been on each other’s radar before that, but we finally met at Paleo f(x), and we hit it off right away. I think we share a similar perspective on a lot of this stuff, and we spent some time together and got to know each other, and then we hung out a little bit at AHS, and we’ve become fast friends. And so, I have a lot of respect for Dan and his work, and I’m really excited to have him here on the show, and I’m gonna have Dan introduce himself and tell you a little bit about how he came to this work and what his perspective is. And then we’re gonna spend the rest of the episode talking about sleep. So, Dan, why don’t you say hello to everyone and tell them a little bit about yourself and where you’re coming from.
Dan Pardi: Great. Thanks for the introduction, Chris. I tell you, it’s a real honor to be here because I learn so much from you and this podcast, so it’s a real pleasure. And I’m excited to talk about some concepts related to sleep today, and yeah, I’ll tell you a little bit more about myself. So I’m a researcher, and I work with the Department of Neurology and Endocrinology at Leiden University in the Netherlands, and I work with the Behavioral Sciences Department at Stanford University. And I look at how chronic sleep deficiency or not getting enough sleep on a chronic basis, how that affects things like decision making and weight gain, just a couple of areas that have been of interest to me for a long time. I got into sleep probably 10 years ago. I was working at a pharmaceutical company that was working in rare disorders and had a sleeping drug for narcolepsy. And with that, I started going to scientific conferences on a yearly basis and was just trying to soak up as much information as I could because as soon as I started to learn about it, the doors opened up and I couldn’t learn enough. It’s an endlessly fascinating topic, I find, and how it leads to personal insight about yourself or others, our health.
And so over time I started to think about — I had done some academic research in the past on lifestyle factors like diet and stress management and exercise, and a lot of these different disciplines that I had explored started to coalesce into some ideas about how to help to facilitate health in others, and I created this model for behavior change, and the idea was that it would look at a variety of different influences on behavior and try to harness those in a way that would enable somebody to live a healthy lifestyle more easily. And from that I started to try to operationalize the model, and friends called it Dan’s Plan because I had talked to them about what I was doing, and the name kinda stuck, and it seemed memorable so I rolled with it. Yeah, so now the idea with Dan’s Plan is simple: We try to take the best practice guidance about what is the information that is most helpful to help us live in a way that is going to facilitate health and try to filter it through this behavioral model, which uses things like behavioral economics and persuasive technology, and the idea is to try to simply a person’s health practice to try to make it as easy as possible for them to live a healthy lifestyle on a day-by-day basis.
So, that’s what we do, and one other thing that I’ll say is that the thesis that we’re working off of is that a lot of modern illness is a result of what we call a broken lifestyle, and that is a lifestyle that is in discordance with our biology and because this is facilitated by a lot of modern luxuries. So instead of having a lot of our health behaviors be predicated on survival behaviors, we now have an option to really not engage with things that keep us healthy. And so, therefore, if you want to be healthy, you have to cultivate and maintain a personal health practice because right now we actually have the option not to, and so we try to look at what are the things that make that health practice effective to keep you free of disease, maintaining full physical function, and have the highest quantity of health within your lifespan. So that’s a little bit about me and what I do.
Chris Kresser: Cool. Thanks, Dan. And for the record, everybody, Dan’s Plan is excellent. I recommend it to all of my patients. It’s the best tool that I know of for tracking the most important factors in changing your lifestyle and meeting your health-related goals, and it’s completely free, so you should definitely go check it out. It’s at DansPlan.com, and you can set up an account. You can set up your weight goals and your sleep goals and your movement and activity goals, and then there are a lot of really cool tools to help you stay on track. There are great emails that he sends out every day with suggestions for exercise and activity and recipes and other hardware tools that interface with Dan’s Plan like the Fitbit and the Withings scale that can make it really easy to track your data and get it up into Dan’s Plan. So, definitely check it out. I think it’s definitely the wave of the future in terms of this kind of tracking.
Dan Pardi: Thank you. Thanks, Chris.
Why sleep is essential to health
Chris Kresser: OK, Dan, so let’s begin by talking about some fundamentals of sleep because I think even though sleep, you know, we talk about it a lot, we hear about it a lot, I think everyone knows a little something about the importance of sleep, there are still some things that we don’t know about sleep, and I find that pretty interesting after all this time researching it. But let’s begin with why do we even need sleep, how does it work, and what are some of the key metrics to consider when we talk about measuring sleep.
Dan Pardi: It’s a great question. You know, this question of the purpose of sleep has really been elusive to researchers, and I think it might actually have to do with the nature of the question itself, as though we’re trying to identify a singular purpose for sleep when really there might be hundreds of purposes to sleep, many, many things that it does to kind of work in a reciprocal fashion to what’s happening during the day so that we are better prepared for the next day once we engage with sleep. So yeah, that kind of grand purpose, it still eludes us, and it’s like every scientific study concludes with “more research is needed.” You know, every time you go down one path, it opens up more doors, and that’s perhaps the frustrating thing about science but also one of the wonderful things, too.
So, the structure of sleep is it’s very complex and active and highly organized. We used to think that sleep was just this period of behavioral quiescence, so the mind and the body kind of shutting down and relaxing, but we know now that there are parts of the brain that are more active during sleep than they are at any other point during a 24-hour period. We also know that the structure and the sequencing of the sleep stages — There are different sleep stages that we go through over the course of the night, and different research will look into, you know, what are the important aspects of these different stages, how about the rhythmicity, so how they flow together. And the three real kind of cardinal features about sleep, the keys, are timing, intensity, and duration. And there’s so much more to talk about, but those three things are really critical. So, timing has to do with your bedtime and your wake time, so that timing within a 24-hour period. Then there is duration. OK, that’s easy. That’s the length of time that you sleep within that period. And then also intensity, which refers to the depth of sleep, and you could spend 8 hours sleeping and if you only stay in the lighter stages of sleep, you’re not gonna really reap any benefits of sleep, so you’re gonna wake up feeling like you got no sleep at all and you’re gonna feel that way, too. So the depth of sleep has been looked at as a marker of quality, but it really has to do with both the depth of sleep, the cyclicity of sleep, so there’s definitely a lot kind of going on there, and the whole conversation would be about just looking at these different structures, but I think that’s probably good.
Chris Kresser: Um-hum. And there are certain health conditions, like I think there’s some pretty interesting research about fibromyalgia and nonrestorative sleep where a lot of people with fibromyalgia are only getting, you know, in stage one, stage two, maybe some stage three, but they don’t go into deep sleep, and their muscles are never able to fully restore themselves, so they have this constant soreness as a result, which I’m sure a lot of people can relate to if you’ve had a few nights of poor sleep, what happens to your muscles and your recovery after that period of time.
Dan Pardi: Yeah, that’s right. Sleep can be truncated, so you can lose sleep by just simply not being in bed long enough, you can miss out on certain stages, or then the architecture or that rhythmicity that I was talking about, so how the stages flow back to back, that can be disrupted, too. And all of it can lead to these cardinal features of poor sleep, so feeling sleepy, mental impairment, physical impairment. So it can get disrupted in a variety of ways, but achieving good sleep is also something that a lot of us can do when we kind of do the right things on a daily basis, and we’ll talk about that further.
Chris Kresser: Yeah, let’s talk about that in particular because I read something a couple days ago, I think, that a third of Americans are getting less than 6 hours of sleep a night, which just strikes me as, like, an alarming epidemic, probably one of the most shocking statistics I’ve heard recently. And if we want to talk about things that are gonna send our health off of a cliff, of course we talk about diet and lack of physical activity and things like that, but I’m thinking that this single statistic is probably scarier than anything else in terms of its potential impact on our health.
Dan Pardi: Yeah, we’re getting 20% less sleep per night on average than we were 40 years ago, and these are statistics from the National Sleep Foundation, which does sleep polls every few years. So around in the 1960s, average sleep times were about 8-1/2 hours per night or least times in bed or self-reported sleep times. And there was an assessment of subjective sleep time in the early 1900s, and it was about the same as it was in 1960, so about 8-1/2 hours. And there has been a slow and steady decline in sleep times, and now the average is 6-1/2 hours per night for working adults, and then about 7 hours and 20 minutes on the weekends and trying to play catch-up.
Chris Kresser: And that doesn’t even reflect the quality of sleep, so it’s possible that those 6-1/2 hours, it’s not only shorter than our traditional norm, but those 6-1/2 hours are poorer quality, I would suspect, than they have normally been.
Dan Pardi: Well, it’s very possible. In some senses, sleep has the ability to almost compress, so it’s compensatory in that when you get less sleep one night, the staging, the depth of sleep will try to do its best to try to get that sleep back, to try to recover lost sleep. But there are also these factors, you know, like one big important factor is light in our environment. In fact, artificial light is listed as a probable carcinogen by the World Health Organization.
Chris Kresser: Wow.
Dan Pardi: And I think that’s because when we have a lot of artificial light in our homes, we’re staring at iPads and TVs, right? We’re getting engaged. Light will directly stimulate the cortex, and it acts like a cup of coffee. So it’s this fallacy to think, well, I’m gonna just read my iPad until I’m sleepy, right? Because it’s keeping you up. And so, even if you’re getting less sleep on a nightly basis, this sleepiness is getting masked by the environment in our homes in the evening, and that can then set your circadian rhythms, which we’ll talk about in a little bit. That can get them off so that the necessary rhythms in the body become out of synch, and there are very real consequences to that, including much higher incidences of cancers, coronary heart disease, metabolic disease like diabetes. So yeah, I agree with you, Chris. I think that this is one of the most significant issues that we’re facing in our health today.
Steve Wright: So when you’re talking about the artificial light and we’re talking about decline of 2 hours plus or minus a little bit from the ‘60s, which I wasn’t around in the ‘60s, but I hear they didn’t have iPads and the TVs were, like, a different type. They were round or something. I guess it was weird.
Chris Kresser: And they weren’t 70 inches on the wall?
Steve Wright: Yeah, yeah, like the programming stopped at night or something and people went to bed.
Chris Kresser: Yes. Imagine that.
Steve Wright: Yeah, so I’m just curious, do you guys really think that the extra 2 hours is also technology based? Are we compounding it? We’re losing hours in bed and replacing those with artificial light hours?
Dan Pardi: Well, there’s probably a variety of things that are culpable in why we’re getting less sleep. One of them, I think a very real issue is our technology because it will mask the sleepiness. Not only is the light going to keep you up and be an artificial stimulant, but also what are you doing? You’re maybe doing work, playing Angry Birds, whatever that is — that’s going to engage you and mentally stimulate you as well, so that’s one thing. But then there are also things like longer work times and longer commute times, and so to some degree, people are trying to just find more personal time for themselves and their family, and they’re getting home at 8 o’clock at night, and they want to have a little time to themselves. So there are those sorts of factors that are also kind of shaping, I think, this new existence.
Chris Kresser: You think there’s been a cultural shift, too, you know like this kind of idea of I’ll sleep when I’m dead and a lot of the biohacking ideas out there where folks believe that they get by just fine on 4 hours of sleep, you know?
Dan Pardi: Yeah.
Chris Kresser: I don’t know. I mean, those trends seem to have been around for a while. I can’t imagine that kind of conversation was happening in the ‘60s.
Dan Pardi: Yeah, I don’t know. It’s interesting, and I don’t know. I don’t know how new they are, but there is that modern mindset of just trying to maximize performance over your day. You know, there’s so much that’s being asked of you. And people sending work emails at, like, 2 in the morning, and there’s probably some subconscious communication about look how hard I’m working, look how dedicated I am. But then there’s also, like, hey, look how well I can do with less sleep. It’s almost like a bravado as well. So there are a lot of different forces that are shaping this, and some of them are kind of, again, subconscious, and some of them are more the mindset that we’re operating under.
Chris Kresser: Yeah. I think there’s a boundary issue with the way that — You know, one of the benefits or the promises of modern technology is that it sort of untethers us from the traditional office environment and 9-to-5 work schedule, but one of the downsides of that is that now, as you’ve pointed out, you can be on vacation, you can be at home at 10 at night, you can be at home on Sunday or out doing errands and there are work emails coming in if you have your phone set up for that, which a lot of people do. And so, you pretty much never have a break, if you do set it up that way, from work, and I think human nature, it’s hard for a lot of people to resist that. If it’s possible, a lot of people will do it. So I personally feel like that has a huge impact on people’s sleep rhythms and just their ability, as you said earlier, if they’re on their iPad and they’re doing something and an email pops in at 10 o’clock at night, it may be hard for them to resist checking it, and then they check it and it’s like a big fire at work that needs to be put out, and so all of a sudden they’ve shifted into a state where they might have been relaxing and kind of getting ready for sleep into like an activated stress response because of something that’s happening that’s work related.
Dan Pardi: I was thinking about something very similar earlier today, Chris, and I agree. In some senses, yeah, it’s this great benefit of untethering us from just being at a desk 9 to 5, but then it follows us everywhere. And I think the only real vacation these days is the one without cell reception.
Chris Kresser: Haha, that’s right! Yeah, I purposely look for places like that at this point. They’re harder and harder to find, though.
Dan Pardi: Yeah, so I think what’s gonna happen is there needs to be some public awareness about some of the negative consequences, particularly within work environments, so showing the employers that if you want a really good, happy, productive person, they need rest, they need an off period, and you have to make it somewhat part of the culture to regard sleep as something that is going to help you perform on a daily basis. You know, like you wouldn’t go to work and have a glass of alcohol. It’s just not culturally acceptable. And so, I think getting sleep time and not sending emails really late at night, that’s going to, I think, hopefully imbue into kind of the work culture and so there will be less pressure to kind of confirm to what your workmates are doing.
The telltale signs of sleep deprivation
Chris Kresser: Um-hum. So let’s just dive in a little more deeply to the consequences of sleep deprivation. I mean, I’m sure most of my listeners have a pretty decent idea just even from their own personal experience, but the research on this is robust, and it’s pretty scary, actually, so tell us a little bit about what you’ve seen in your research and just your awareness of the overall body of literature.
Dan Pardi: Yeah, the effects of sleep will affect almost all body systems and tissues, and I think we’re still uncovering and unraveling the effects of sleep loss on our health, and I think there’s probably some impairments and consequences that are taking place that we’re not even fully aware of. But you see very meaningful, consistent clinical data showing cardiovascular risk, metabolic risk, premature aging and cancers, problems with the brain, so it’s almost hard to find some tissues or systems that aren’t really affected with chronic sleep loss, but then again, it’s also newer, right? So we’re getting less sleep as a society, and it’s continued to go down over the last 20 or 30 years, and so right now we’re at the lowest average that has ever been recorded, and so the results of today, it’s unprecedented. We don’t know what’s really gonna happen and how severe it can be.
Chris Kresser: Really it’s a big society-wide experiment.
Dan Pardi: Yeah, exactly. That is life today, haha.
Chris Kresser: In a number of respects. So how about more particularly on weight regulation? I saw a pretty interesting quote — I think you sent it to me — from a study that said in that study sleep deprivation was more of a risk factor for obesity than fat intake or lack of higher intensity exercise.
Dan Pardi: Yeah, this has been a line of research that has gained a lot of visibility over the last probably 10 years, and it started with — There were several different studies, but one of them was the Wisconsin Cohort, which looked at 15,000 people and noticed that if you did a trendline, those that actually slept less tended to be higher weight and had a much higher risk of being overweight, and it was actually this sort of U-shaped curve. So the extreme long sleepers, they also actually had higher weights as well, and the average right around 8 hours was the people that maintained the lowest weights. And so these studies were followed up with short prospective-term studies where they took healthy young men and they would subject them to, you know, 4 hours of sleep per night, and then they would monitor some of their homeostatic hormones like leptin and ghrelin, and they noticed that both leptin and ghrelin, which affect feeding, energy regulation, sympathetic nervous system activity — all things that will eventually help to control or influence body weight — would adjust in a manner so that you were more likely to be hungry and more likely to be storing fat, and less likely to be burning energy. So that’s been followed up multiple times both in animal studies and in humans, and additionally we also see that there is a pretty immediate and significant impairment in glucose regulation. So the thinking is that chronic sleep deficiency is going to not only predispose you to obesity, and by the way, 81 out of 89 studies that have looked at this have found positive findings, and the risk seems to be that lack of sleep or chronic sleep restriction will increase your risk for obesity about 55%.
Chris Kresser: Wow.
Dan Pardi: So it’s really, really meaningful, this connection. How it’s happening, I think, is still being discovered. But certainly, you know, the sympathetic nervous system is an autonomic process that will be much higher during the day or when you’re awake, excuse me, more active during wakefulness than it is during sleep. And so, as we truncate our sleep times, you’ve got longer periods of the sympathetic nervous system activity, which might have this downstream effect on cells or on cortisol. One of the downstream effects actually is cortisol, and we know that if you have higher levels of cortisol circulating, like Cushing syndrome, you can induce insulin resistance and rapid fat gain. So those of some of the areas that have been explored, but there either seems to be a clear connection between sleep loss and weight gain, and also there seems to be one between sleep loss and the increased risk of diabetes, as well.
Steve Wright: Hey, Dan or Chris, one of you two guys jump down that rabbit hole, so when poor sleep or chronic low sleep messes up my ghrelin or my leptin, which one’s gonna be appetite regulation, the other one’s gonna be appetite regulation as well kind of, tell us when we’re not sleeping correctly, tell me what’s gonna happen during the day, what body functions are gonna malfunction because of these hormones?
Chris Kresser: Dan, maybe you could address that in relation to your research on sleep and appetite and decision making.
Dan Pardi: Yeah, sure. These hormones will display 24-hour cycles, and so leptin will gradually rise from the morning over the course of the day, and then it will peak somewhere in the evening, and ghrelin will follow a little bit of a different pattern. It’s considered an episodic hormone, in that it waxes and wanes depending on food intake over the course of the day, but it also seems to peak in the middle of the night and then decrease. And ghrelin is a fascinating hormone, actually, because it’s released from what are called oxyntic cells in the stomach, and it’s thought that it will stimulate hunger. So when there’s lack of food in the system for a period of time, ghrelin levels rise, and then that will make you hungry. But it also is then involved in things like reward, so it has a lot of effects on cognition as well, and it’s involved in memory and reward processing, so anyway, lots of interesting stuff that’s going on there.
But there’s different ways that this can kind of be messed up. When you have less sleep, you actually affect the daily rhythms of both of those hormones, so with 2 hours less sleep per night, there’s about a 15% decrease in leptin and about a 15% increase in ghrelin, so one goes up, one goes down. Both of them, again, would predict that you would be hungrier, and that is what some research has seen, is that people tend to be a little bit more impulsive and they tend to crave what’s usually found is high-carbohydrate food. And that may or may not be true, but what my research is looking at is, is it that they’re craving high-carbohydrate food or are you actually just more impulsive? And a lot of high-carbohydrate foods in our cupboards, for example, they tend to be: open package, eat. Right? In the typical American home. So is it the carbohydrates or is it kind of the quickness? You know, it’s many more steps to prepare a meal, but just opening a drawer and eating something, what we know is that sleep loss makes you much less likely to make an effort for a reward. And it’s called effort discounting. And so, you just want to basically find the fastest path to make you happy because you don’t want to work for it. So that’s what my research is looking into.
And I’ll share another example that is not specific to weight gain but is really interesting, and I won’t go too nerdy here, but I’ll mention these two parts of the brain. So one of them is called this ventral medial prefrontal cortex, and it actually is a part of the brain that is known for what’s called the neural correlate, so this is the area of the brain that is thought to represent the estimation of gains, so if you’re in any sort of risky decision making, like gambling, right? If you’re about to say how much can I win? Then this area of the brain is very responsive. A counterbalancing part of the brain is called the anterior insula, and that’s thinking about all the consequences of gambling. And when you’re sleep deprived, then the area that is encoding possible gains becomes very active, and the area that’s encoding possible losses becomes not very active at all. So if you think about when casinos make a lot of their money, it’s late at night, right? You’re sleep deprived, right?
Chris Kresser: Yeah.
Dan Pardi: Probably you have alcohol in you, too, if you’re in a casino. And you’re much more likely to make a gamble that you ordinarily would never do. Now think about how that translates into everyday life where in this obesogenic environment there’s food everywhere. Are you less likely to say no to the candy bowl as you pass it? You’re not thinking about the consequences.
Chris Kresser: That explains why people eat that food at the casino buffet.
Dan Pardi: Something has to explain that!
Steve Wright: Does lack of sleep also lower dopamine? Like, are these people also kind of craving a possible dopamine hit? Is that part of it?
Dan Pardi: It’s an interesting question. You know, this guy David Rye is one of the foremost dopamine researchers in the world, and he — It’s funny, haha. It’s a good question. He would roll his eyes at it because he gets really frustrated because dopamine doesn’t do just one thing in the brain. Actually the levels stay relatively constant, particularly compared to other neurotransmitters, particularly over a 24-hour period. And in some areas it’s promoting inhibition, in other areas it’s more excitatory, so it’s hard to think of dopamine as doing one thing. It actually is having kind of pervasive effects throughout the brain as basically a signaling molecule. But we do tend to think of it as being related to pleasure and reward, and there is some idea that that might actually be a possibility, and we do know that one thing that does affect dopamine signaling is light, so as you can see with seasonally obese animals — these are animals that become obese during certain parts of the season — you’ll see a drastic reduction in dopaminergic signaling in the master clock in the brain. So dopamine signaling goes way down, and that probably has been signaled by alterations in the light-dark cycle as the seasons change. But the corresponding change in the brain is there’s this big increase in noradrenergic or norepinephrine, another neurotransmitter in another part of the brain that is involved in feeding. And so, in these animals, without any increase in food intake, you see the induction of metabolic syndrome. They become hypercholesterolemic, they have insulin resistance, they gain weight immediately, and basically this is the mechanism by which the brain helps them store energy for the winter. So could that actually be happening with us with these altered light-dark cycles? And we’re not seasonally obese animals, but we also don’t really fully appreciate or understand the effects of the seasons on our health and our rhythms because it’s just hard to study. So I’m not sure if that answered your question, but yeah, it’s some interesting dopamine research.
Steve Wright: Yeah, super interesting. Wow.
Dan Pardi: Yeah.
Does light play a role in getting better sleep?
Chris Kresser: So let’s talk a little bit more, we touched on this before, but about exactly how light does influence sleep rhythms and hormones that regulate sleep like melatonin and cortisol.
Dan Pardi: Yeah, so light will enter into the eye, and it affects the specialized cells that are called intrinsically photosensitive retinal ganglion cells — not important, but a nice long scientific word. And those will transmit their signal back into the hypothalamus, which I’ve heard you talk about, of course, on the show before. And near that hypothalamus is this suprachiasmatic nucleus, the SCN, and that is the master clock in the brain — and the body. So this is affecting the rhythms throughout the body. And the way that it works is that that master clock, through the communication of light through the eye, will synchronize to the light-dark cycle of a 24-hour period. So the clock in the brain synchronizes with the environment, and then all of the clocks — because there’s a clock in all cells in the body — will then synchronize with the master clock. So there’s two synchronizations taking place: our brain with the environment and then the clocks throughout the body with the master clock in the brain. And what you see is that we know that at certain times of day, of course at night, melatonin levels go up, body temperature starts to drop, cortisol levels are low, and what happens is at different parts of the day there are different phase relationships. So usually if you go to bed hours later than you used to, you’re gonna end up sleeping in a different hormonal milieu, right? A whole different hormonal soup than you would if you have gone to bed at the time that you usually do. Now whether or not that is pathological — I think that there’s some evidence that suggests that it is, but that is one thing that is — I’m suspicious of that. But anyway, that is one way that light enters into the eye and affects these rhythms.
Steve Wright: So is it all light? I’ve heard a lot about this just being a blue light problem. Or is it any light?
Dan Pardi: Yeah, it’s a great question, because there’s definitely an emphasis in discussions around this around blue light, and the spectrum of light does matter. But the things that do matter are the intensity of the light, the wavelength or the spectrum, and then the duration or how long light is acting on the eye. So the intensity is actually very — If there’s any light at all, then it’s entering your eye. If you can see at all, light is entering your eye and it has the potential to affect your rhythms. But most potently, blue light will affect your circadian rhythms more than anything else. So you can think of, well, during the day we’re getting a lot of bright, blue light, which makes sense being outside. That’s going to, again, be a direct stimulator of cortical activity. So if you want to feel like you’re having a cup of coffee, get outside, walk around, get some light in. And outside light is much strongly intensity than inside light, and more so than it even appears so. The intensity of light is measured on a logarithmic scale, so outside light is measured in lux, and it can be over 100,000 lux, where in a room inside light is 200 lux, so it’s much, much lower in intensity. And intensity definitely shifts our rhythms.
And we know that if you’re outside during the day, then you’re gonna have a much more robust melatonin rhythm at night. So being inside during the day will decrease your melatonin at night by about 50%, so what we end up having is this process unfortunately of asynchronization, and what I mean by that is we’re spending a lot of our time indoors during the day, right? With not a lot of light and not a lot of physical activity. And then in the evenings, we’ve got a lot of artificial light and a lot of things that are stimulating and keeping us up. And at night, we might have also clocks and windows open and other sorts of light, a nightlight on. That itself can also suppress melatonin. So not getting enough daytime light will suppress melatonin, getting too much night-time or evening light will suppress melatonin as well, and so overall — You know, we know melatonin is a really fascinating hormone. It has a lot of potential positive effects, particularly on cancers, and it is an antimicrobial agent. And if we’re getting the natural amount of darkness in a natural living environment is somewhere, depending on the seasons, like, let’s say 10 hours, we’re not getting 6. We’ve truncated that by 4 hours per night. We’re not getting the benefit of that hormone acting throughout the body and having the ability to kind of exert its benefits.
Chris Kresser: Yeah, and that’s, of course, what you described: not enough light during the daytime and too much light at night. That’s probably one of the primary factors of the modern lifestyle that’s driving this sleep epidemic. Someone who goes to work in an office and is exposed to artificial light or very little natural light during the day and then they go home and the iPad and all the various technological devices emitting light, and it’s kind of a double-whammy effect.
Dan Pardi: Yeah.
Steve Wright: Dan, so what Chris just talked about, I’m sure a lot of listeners, including myself, are in that situation. Is there is a minimum level of daytime light we should try to achieve?
Dan Pardi: You know, that’s a really interesting question, and I don’t know we have an answer to it. What is that minimal threshold that we need to surpass in order to maintain these normal rhythms? Well, I would say that getting morning light is definitely important. That serves as an anchor. So I think waking up in the morning, getting outside, and getting light for a good 10, 15, or 20 minutes is a really smart thing, particularly if you do any fasting, by the way. I do intermittent fasting myself, and I think that there’s some really interesting science behind it. I know it’s not for everybody, but I’ll just bring it up to mention that if you do do fasting, then it is important, I think, to get bright light exposure first thing in the morning, because what a lot of people might do if they’re fasting is that their circadian rhythm will shift, right? The body is always trying to listen to understand what part of the day are we in? Like if you travel to Europe or basically you change time zones, over time, the body is taking in signals, not only light but also sleep, physical activity, food, those to a lesser degree than light, but they are affecting the circadian rhythms. They’re gonna eventually help you shift and get onto that schedule where that schedule now feels normal. So all of those things really do matter, and actually you see this in people that will do fasting for religious purposes. What happens is that — it’s usually a month long — over the first couple of days, they basically shift their schedule. So even though they’re fasting, they’re able to eat at night, and so they end up being up at night much longer than they normally would be if they weren’t fasting. So be careful of that. Get a lot of bright light exposure if you do fasting, particularly in the morning. And then I would also say getting outside a couple of times a day whenever you can does make sense.
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The truth about polyphasic sleep
Chris Kresser: Um-hum. So I’d like to move this into a more practical direction, but before we do that, I want to talk a little bit about biphasic and polyphasic sleep. I know we both saw this article in the New York Times last Sunday — maybe some of you all saw it — that was saying that we don’t really need 8 hours of continuous, uninterrupted sleep and that from an evolutionary perspective that probably wasn’t natural. So what do you think about that, Dan, and if that’s even true and how applicable it is to our modern situation?
Dan Pardi: Yeah, so the author, David Randall, wrote an interesting article, and there are a few things that I thought were really good points, and there were a few things that I thought were not accurate. And this is actually similar — A BBC article came out probably six or eight months ago, and it was very similar to this, and it talked about this first and second sleep. And it was referencing the work of a historian from Virginia Tech — I’m trying to remember his name. It’s Ekirch, I think. And this researcher was looking in historical texts, and he kept noticing references to this first period of sleep and second period of sleep, and basically what he identified is a natural sleeping pattern for people pre-Industrialization, pre-modern lifestyle, where they just had candlelight, is they would go to bed soon after sundown, they would sleep for a period of time, then they would wake up and have this alertness in the middle of the night, and then they would go back to sleep and sleep for the remainder of the night. And both articles seemed to suggest that that is the more natural pattern, and they used that as a way to condemn the 8-hour monophasic, consolidated chunk of sleep. And I don’t think that the evidence supports that. Right? Just because there are suggestions that an alternative or another pattern of sleep and wake might not have any harm, you’re not necessarily condemning the 8-hour monophasic sleeping in one 8-hour chunk.
Chris Kresser: Right.
Dan Pardi: The point that he brings up is that when you get really concerned about getting your 8 hours, it can cause anxiety, and without a doubt, that’s a good point. Cliff Saper, who is the Dean of the Harvard Neurology Department, said insomnia is an anxiety disorder. First and foremost, that’s what it is. And people get worried about something, and they start to ruminate on an idea, and then eventually whatever was the kind of instigating stimulus that stimulates the insomnia, eventually it can just turn into this positive feedback loop. Now you’re worried about the insomnia, and that’s preventing you from sleeping. So anxiety is a problem, for sure, for people that have insomnia. And we all experience that every once in a while, in some people for frequently, for sure. But I think that, as we discussed earlier, the real problem in our society is lack of sleep, so we’re not getting enough sleep on a nightly basis. At least it seems that way. And we’re getting enough sleep to a degree that we will see very significant impairments in cognition if you were to look at those same situations under lab conditions. And so, an awakening is not an awakening. Right? If you are getting all the sleep that you need and you wake up in the middle of the night, OK, then that’s fine. You don’t necessarily have insomnia. But if you are not getting enough sleep and you still can’t sleep, then that doesn’t mean that you don’t need that sleep. It might be that you have temporarily a sleep issue. So I think that there were a couple points that weren’t made as well as I would like for him to have. What were your thoughts on the article, Chris?
Chris Kresser: I thought it was just an interesting historical perspective, but I didn’t really see anything in there — I mean, even if we’re talking about pre-Industrialization, that doesn’t necessarily give us any insight into what was happening pre-Western civilization. And I think obviously we’re in a really different place right now, and so even if a biphasic sleep pattern worked in a pre-Industrial society where people were getting more sleep overall and probably having maybe more sleep during the day and leisure time — You know, I think one of the things that that article pointed out is that even still in several other cultures it’s acceptable to take a nap during the daytime even at the office. You know, people just put their heads down. So it was interesting to me, but the question definitely arises of how applicable sleep patterns in pre-Industrial civilization are to our current situation now.
Dan Pardi: Yeah, and that’s a great point. There’s a model called the two-process sleep and wake model, and I think it’s actually really illuminating for this topic. This was a model that was published by a researcher, Alexander Borbély, in 1983, and it is the most cited sleep article, I think, that we have today. It’s incredibly influential in our understanding about how sleep works. So in that model there are basically these two different processes that are influencing your levels of sleepiness or alertness at any point over a 24-hour period. And the first process is called sleep pressure. It’s this type of theoretical construct to explain this observation that we see in various elements of the lab. I won’t go into that, but the idea is that sleep pressure builds from the moment you wake up. It builds, builds, builds. However, you don’t necessarily feel sleepier and sleepier from the moment you wake up, not at all, right? Usually you might have a little inertia, which means you’re a little groggy for the first hour. That’s totally normal. Not everybody experiences that. But then you stay somewhat stable over the course of the day. And that’s because there is this opposing force, which is called your wake drive. And your wake drive is basically counterbalancing this building sleep pressure. And then in the evening the wake drive will actually dissipate. It waxes and wanes. It has this cyclicity. And now all of a sudden you have this unopposed sleep pressure, and that facilitates sleep onset, and it also will help to maintain sleep maintenance if you have enough pressure.
So what happens if you take a nap during the day? Well, you wear off some of that sleep pressure, all right? And a lot of people, if they’re not getting enough sleep on a nightly basis, then that’s okay. They’re actually helping to wear down some of their sleep debt, and they have really measurable performance improvements. The other way to do that is to sleep longer at night. But for people that are getting fully sleep satiated, if you take a nap in the afternoon, then what you’re gonna see is the sleep latency or the time to fall asleep is increased. And then also if you wake up in the middle of the night, you might not have enough sleep pressure to maintain sleep throughout the night. And so, that’s the model that we’re really working with, and then we have to think about how that then fits within the society. Are we talking about if you referenced in China, India, or Spain, where they allow for naps? You know, let’s say you become dependent on a nap, but your culture, society, or your workplace, you don’t actually get that on a regular basis, behaviorally you maybe come to expect a nap at 3 o’clock, and if you don’t get one you’re gonna practically fall asleep in your meeting. So it kind of depends on the context of the culture that you’re in, too, whether naps are beneficial or not.
Simple tips for getting better quality sleep
Chris Kresser: OK, this has been fascinating, and I would love to now maybe just spend a few minutes breaking this down into some tips that people can follow in terms of ensuring good sleep hygiene. Obviously we can’t address all of the issues that can cause problems with sleep in 5 minutes, let alone a single podcast or even 10, but maybe just some general guidelines for ensuring good sleep. You talked about the importance of getting some light exposure in the morning and throughout the day, but what are some other things that you talk about within the context of Dan’s Plan?
Dan Pardi: Yeah, sure. So kind of going back to operationalizing sleep, how do you then try to get the best outcome with the knowledge set? So you believe now, OK, sleep’s important. I want to get the best sleep that I can. What do I do? Well, we look at day, evening, and night as opportunities to affect this process. And as we talked about in the beginning, timing, intensity, and duration are three of the most important things to focus on. Most people have an idea about duration, or at least you can think about it. So over the course of a week or two, you can think about how much sleep do I need to get for me to feel my best? And then you can backtrack because a lot of people have fixed wakeup times either due to work schedules or school schedules, so you can then work back and say, OK, if I need 8 hours of sleep, then I know that I need to go to bed at 11 o’clock. And what you do is you form an intention, right? Now you have a clear, tangible time in your mind. That’s your goal. You want to be in bed by that time. And that’s really important because remember, as we’re up at night, if we’ve got other sorts of stimulating influences like television, etc. — Like, let’s say if you do watch TV at night and you’re deciding on whether to watch another episode and it’s 10:45, but you want to be in bed at 11, well, if you didn’t really have a clear objective in mind, it would be very easy to just put on another show. But if you do and you care about that, now you’re getting consistent timing because we try to gamify that. We color-code your score around your bedtime based off of how close you are to it. So that kind of makes it more interesting and relevant and salient. So that’s one thing that you can do, and it actually addresses basically two out of the three: timing, so that’s the time that you go to bed, and then the duration.
And then the third one is intensity, and that has more to do with the things we were talking about earlier. You can’t get more sleep by squinting harder, right? I mean, it’s not an action, but there are actions that you can do in the beginning of the day that can facilitate that. And what we know is that sleep is dependent on the usage of our body and mind over the day. So when you get more physical activity during the day, you will fall asleep sooner and you’ll stay asleep longer. Light exposure first thing in the morning. We talked about how that affects melatonin. Of course, melatonin will influence sleep rhythms and circadian rhythms. And I think the other thing is controlling your light environment, getting light in the morning, outdoor light several times during the day. Try to have bright light at your office place. And then in the evening, tone down the lights, change the tone of the lights from blue to more amber tones, and then at night try to keep your sleep environment cool, calm, quiet, and dark. Those are the things that are gonna help to facilitate really good sleep while you’re in bed. But you see that most of that guidance is happening outside of bed, right?
Chris Kresser: Um-hum.
Dan Pardi: Those are the things that you can, I think, really do to try to nurture and encourage good sleep on a daily basis. But just prioritizing it, recognizing it’s important, forming that intention about what time to go to bed, doing some tracking, which is really simple, but then it’ll help to create mindfulness about if you’re doing it or not. It can make a huge difference. And we need tools that help counteract these forces and stimuli that keep us up. So I would say count on that you do, right? Because these things are very persuasive. And again, it’s easiest to go to sleep when you’re sleepy, but there are reasons why we don’t necessarily feel sleepy while losing sleep.
Chris Kresser: Well, I think that really sums up some of the best approaches you can take, and a lot of it seems to really boil down to awareness and intention.
Dan Pardi: Yeah, forming that intention, being aware of yourself. And I’ll share an anecdote: There’s not a linear correlation between knowledge on a health subject and how healthy you are, right? And just because you know a lot about something does not necessarily mean that you’re going to live that lifestyle that’s gonna facilitate that. The professor emeritus at some university on nutrition doesn’t necessarily have the best nutrition herself. So the point that I’m making is that a while ago, I’d been coaching and educating on sleep, and if somebody asked me how much sleep I was getting, I would’ve told them 8 hours, absolutely. But I was tracking my sleep, and I was getting just over 7. So I was getting basically an hour less than I thought I was. And so that tracking can really help you understand what’s really happening versus what you think you’re doing. And so it just makes it a lot easier to then do some course correction so that you can say, OK, you know what? I’m not getting quite the sleep that I need, that I know that I need for me to feel my best, so let me make some adjustments. And I think that that can keep us on track.
Chris Kresser: And that’s, of course, equally true for physical activity, I think, which we’ll have to have you back on to talk about another time.
Dan Pardi: All right, I’d love to.
Chris Kresser: Well, thanks for coming on the show, Dan. It’s been great. I really appreciate your time, and I look forward to the next time we can have you on.
Dan Pardi: Thanks so much, Chris. It’s a real pleasure for me.
Chris Kresser: So everybody, check out Dan’s Plan, again http://www.dansplan.com. You can sign up for an account there for free and get started tracking all this stuff and set your goals for sleep and activity and weight. And if you’re like the vast majority of my patients, it’s gonna help you a lot. So that’s it for this week. We’ll see you in a couple weeks.
Steve Wright: That was a fascinating show, and I hope that everyone enjoyed it as much as I did. And we want to thank you for listening today, and please keep sending us your questions to ChrisKresser.com using the podcast submission link. If you enjoyed the show, please head over to iTunes and leave us a review. It helps us with our rankings and helps the show reach more people so we can change more lives. Thanks. We’ll talk to you soon.
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