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Yes, You Still Need 7-8 Hours of Sleep—with Dan Pardi


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Dan Pardi and I interpret the recent UCLA sleep study and discuss how it impacts those of us living in the industrialized world. What factors are important when it comes to sleep and what did the study not tell us?

Revolution Health Radio podcast, Chris Kresser

I’m sure by now many of you have heard about the recent study that came out of UCLA that looked at sleep patterns in three different hunter-gatherer groups, and the way that the media is reporting on this study suggests that despite a lot of recent evidence and claims that humans need 7 to 8 hours of sleep to function properly, which I’ve been an advocate of in my book and elsewhere, that in reality our ancestors may have only slept 5-1/2 to 6 hours a night and get even sleep than most of us in the industrialized world get today. So I wanted to invite Dan Pardi, a sleep expert that we’ve had on the show before, back to discuss this study and its implications for those of us that are living in the industrialized world.

In this episode, we cover:

What the UCLA sleep study says
Important sleep factors
What the study did not tell us
Sleep recommendations while traveling

Links We Discuss

Chris Kresser: Hey, everybody, it’s Chris Kresser. Welcome to another episode of Revolution Health Radio.

I’m sure by now many of you have heard about the recent study that came out of UCLA that looked at sleep patterns in three different hunter-gatherer groups, and the way that the media is reporting on this study suggests that despite a lot of recent evidence and claims that humans need 7 to 8 hours of sleep to function properly, which I’ve been an advocate of in my book and elsewhere, that in reality our ancestors may have only slept 5-1/2 to 6 hours a night and get even sleep than most of us in the industrialized world get today. So I wanted to invite Dan Pardi, a sleep expert that we’ve had on the show before, back to discuss this study and its implications for those of us that are living in the industrialized world.

Dan is an entrepreneur and researcher whose life’s work is centered on how to facilitate healthy behaviors in others. He’s the CEO of humanOS.me and DansPlan.com, health technology companies that utilize the Loop Model to Sustain Health Behaviors, which he developed to help people live a healthy lifestyle in the modern world. He does research with the Psychiatry and Behavioral Sciences Department at Stanford and the Departments of Neurology and Endocrinology at Leiden University in the Netherlands. His current research looks at how sleep influences decision making. Dan also works with Naval Special Warfare to help the most elite fighters in the world maintain vigilant performance in both combat and noncombat conditions. You can follow him at DansPlanHealth on Twitter.

OK, so without further ado, let’s talk to Dan about sleep.

Dan, welcome back to the show. Pleasure to have you on again.

Dan Pardi: Chris, thanks for having me back. It’s great to be here.

What the UCLA Sleep Study Says

Chris Kresser: I invited you to come back on the show so we could talk about this new study that just came out that’s making a lot of waves in the media by Jerome Siegel, I think he was the lead author, from UCLA. And as I’m sure most people who are listening to this have heard, the way the media is approaching it typically is, “Hey, contrary to popular belief, we have a lot of people who have been saying that our ancestors got more sleep than us, maybe 8 or 9 hours a night, and this new study shows that, on the contrary, many of them actually get as much or even less sleep than we do in the West, and so we basically just need to throw out everything that we knew before about sleep and ancestral sleep patterns, and anyone who’s out there just sleeping 5-1/2 or 6 hours a night is fine because this is what these three hunter-gatherer cultures do.” What’s wrong with that picture, Dan, and way of interpreting that study, which we’ve seen over and over now in the media?

Dan Pardi: Yeah, it was a huge popularity last week and for good reason. It’s a really interesting study, but it’s also easy to misinterpret. The question I get most regularly and probably the easiest question to ask is, how much sleep do you need? And it’s actually one of the hardest questions to answer because it’s dependent on several things. But I’ll talk a little bit about the details of this study. Then we can talk about its interpretation.

As you mentioned, there were three hunter-gatherer groups that were analyzed, and they were analyzed through what’s called wrist actigraphy. This is a wrist-worn device that will look at movement patterns, sleep patterns, and then some new ones also look at light, so just by wearing it, it has a light meter. And what they can do is then they can look at periods where they will use that motion data to then predict, OK, were they asleep or not, maybe what type of sleep were they in, and then what were their physical activity patterns like, and then also what kind of light exposure did they get.

The three groups that were studied were the Hadza, which are foragers of Northern Tanzania; the San, which are hunter-gatherers in Namibia, they’ve been in the Kalahari for tens of thousands of years; and then the Tsimane, which are semi-nomadic people out of the Andean foothills in Bolivia. So those are the three groups that were evaluated, and they were all relatively fit, and I do have some comments to make about what “fit and healthy” means.

Chris Kresser: Mm-hmm.

Dan Pardi: Maybe while I’m on that point I’ll just mention them. Their fit and healthy people might be healthier and fitter than our people. Fitness was actually discussed a little bit in the study, but because unhealthy people in hunter-gatherer tribes will die young, or can, then a lot of people that have health issues are not kept alive through modern medicine, which is a great thing, but there might be some population differences when we say “normal healthy subjects” in a study with hunter-gatherers and then in a study within the United States or some other developed country.

Chris Kresser: Right, because previous work has shown that hunter-gatherers are typically much healthier overall than Westerners when you look at measures like body mass index and oxygen consumption and vision and bone density and things like that.

Dan Pardi: Yeah, so you have to take that into consideration when we’re thinking about these terms that are used to described actually different groups.

Chris Kresser: Right.

Dan Pardi: Normal, healthy. It’s relative.

Chris Kresser: Not to mention the vast difference in just about everything about their lives!

Dan Pardi: Truly, yeah.

Chris Kresser: That can be measured. Yeah. OK, so go ahead.

Dan Pardi: It’s so true! Yeah.

Chris Kresser: Just to throw this in, I was driving back from San Francisco just now and was listening to Science Friday recorded from last week, and they were interviewing this psychologist who studies the psychological and physiological impact of the built environment, and they actually had people take these guided walking tours through New York City in the Lower East Side, among other cities, and they had skin…

Dan Pardi: Bioimpedance monitors?

Chris Kresser: Yeah, bioimpedance monitors to measure the activation of the sympathetic nervous system. They had other heart rate variability monitors. They had a number of monitoring systems to see what was happening to their nervous systems as they went through these different kinds of environments. So they’d have them stand, like, in the middle of a busy intersection, not in the street, but on the center divider. They’d have them stand inside of a green-space park. They’d have them stand at the entrance of different kinds of buildings. And what they found, unsurprisingly, was that the different environments profoundly affected the nervous system.

Dan Pardi: Yeah.

Chris Kresser: In a dramatic way. Like, even just two or three minutes sitting on a park bench in green space dropped the sympathetic arousal by a huge amount, really unexpected, actually, even to the researchers. It just stands to reason to me that the nervous system of people in our highly manufactured built environment and industrial environment is going to be profoundly different than the nervous system of people living in these more traditional settings.

Dan Pardi: I did not hear that. I’m going to go find and listen to it. But it’s also very consistent with other reports where you see things like ego depletion happening, which is basically the sapping of your willpower. That happens a lot less when you’re exposed to natural environments or in natural environments. So if you’re doing the same sort of depleting task, if you’re in a natural environment, it’ll happen less.

Chris Kresser: Right.

Dan Pardi: Just one more example about how… you know, our physiology evolved in a condition that’s very different than what’s normal now for many people, so yeah, that’s really, really interesting.

Chris Kresser: So there’s the context, everyone. And Dan’s going to continue—after I’ve interrupted him six times!—and tell us more about this study.

Dan Pardi: No, it’s a really crucial point, so thank you for mentioning it!

Important Sleep Factors

Yeah, so they examined their sleep duration and timing, and as you’ve probably heard me say before on your show and even in the article that I wrote, timing and duration are very key and they’re independent. Duration is easy. It’s the amount of sleep that you get over the course of a 24-hour period. Timing is when that sleep is occurring within the 24-hour period. They looked at both of these factors in relationship to natural light and ambient temperature and then also seasonal changes.

That’s basically the context of the study, and in the big-picture findings is that all three of these groups showed very similar patterns, almost identical. They were all distanced by, you know, there’s a geographical difference for all of them, and the idea is that this might suggest that these people are expressing what is kind of a human, Homo sapiens sleep—the real core, natural sleep—which I think is really an interesting… I wouldn’t say “finding,” but interpretation.

Chris Kresser: Right.

Dan Pardi: Yeah. So what did they find? There are a lot of ways that natural sleep, we’ll call it, is discussed, and oftentimes, depending on who’s discussing it, it can be misinterpreted or, even worse, it can just be wrong in how somebody’s phrasing it. For example, hunter-gatherers would rise with the sun and go to bed when the sun would go down. We know that’s not true. Even though they might not stay up as late as we do when we have artificial light that is stimulating arousal, we also know that hunter-gatherer groups would gather around fires and tell stories and dance pretty late, so it’s not just going to bed right after the sun went down. And in this study they found that, indeed, on average these groups would go to sleep about 3-1/2 hours approximately after sunset. I thought that was pretty interesting.

Chris Kresser: Yeah, me too.

Dan Pardi: Yeah.

Chris Kresser: What are they doing? They’re not watching TV, Dan.

Dan Pardi: Yeah, they’re dancing! If you’re going to stay up past dark, you should go dancing.

Chris Kresser: You’d go dance around the fire, right?

Dan Pardi: Yeah. I totally support that.

Chris Kresser: Mm-hmm.

Dan Pardi: They also did not wake up with sunrise, but would actually wake up before it. And what was really, really interesting to me was that what correlated most strongly with the time that they would fall asleep and the time that they would wake up was actually body temperature… and ambient temperature, and how the sleep onset and sleep offset took place when there were drastic changes in ambient temperature, suggesting that as it’s dropping later in the evening, then that would be a time for energy expenditure within a human to decrease, and this initiates the sleep onset period.

Chris Kresser: This is why you often hear the recommendation of sleeping in a cool room rather than a warm room.

Dan Pardi: Yeah, that’s right. And another recommendation as well, which is if you’re having some trouble sleeping, sometimes taking a hot bath or getting out of a hot tub can facilitate sleep onset, the reason being that when you go into a hot bath, you will vasodilate, and so that allows more core blood to go into your periphery, and when that happens because you’re warm, your body wants to try to actually get rid of body heat. You step out of that hot environment, the heat leaves your body, and you have a drop in core body temperature, and that can make you really drowsy. Anybody that’s ever gotten out of a hot tub at night might feel drowsy and groggy, and that’s one of the reasons why, particularly if they go into a colder environment.

Chris Kresser: Mm-hmm.

Dan Pardi: Yeah. So that is a couple of examples about what can help. Another thing that also can help is taking a half of an aspirin, and that can lower core body temperature, and that can facilitate sleep onset. That’s again going back to temperature here.

They also noticed that when people would wake up, it had to do with when temperatures were rising and not necessarily when the sun was rising. So when it was starting to get a little bit warmer, they would experience vasoconstriction, and that would then be alerting.

Now let’s talk about, maybe, the sleep periods. So how long was sleep duration? This was the big kind of main point that was discussed within a lot of the popular press articles.

Chris Kresser: Right.

Dan Pardi: Sleep duration ranged from 5.7 hours to 7.1 hours, and that sounds pretty low, and in fact, a lot of the commentaries were that this is kind of near the low end of modern cultures, this range. But what’s really important to note is that the sleep period—so there’s sleep duration, which is how long you slept, and then there’s the sleep period, which is the time that you were actually sleeping, the period of time that you were sleeping. That was really average. That was 7 to 8-1/2 hours per night, which is what I recommend.

Chris Kresser: Mm-hmm.

Dan Pardi: Because what’s happening to your sleep in that period is difficult to say. There are a lot of things that are going to influence it. Sometimes you’ll sleep more, and sometimes you’ll sleep less, but you want to give your body adequate time for what I call “complete sleep,” which is allowing all of the homeostatic, physiological processes that are taking place during sleep to not be interrupted by artificial means, like an alarm clock.

Chris Kresser: Yeah, and let’s be realistic about this. When most people hear the instruction to get 8 hours of sleep, they’re going to go to bed at 10 and get out of bed at 6. They’re not going to be determining how many of those 8 hours they’re actually… you know, they’re not going to go to bed at 9 and wake up at 7 so that they can get 8 hours of sleep. Most people don’t think about it that way.

Dan Pardi: Right.

Chris Kresser: But that’s probably what is actually happening. Very few people are going to go to bed at 10 and wake up at 6 and actually get 8 hours of sleep in that interval.

Dan Pardi: That’s right. Yeah.

Chris Kresser: So this study… from a practical perspective, it doesn’t change what the recommendations have been and what you’ve been saying and I’ve been telling my audience for some time now.

Dan Pardi: Yeah, that’s right. An important point was brought up in the study in that let’s say you’re monitoring your sleep and you’re showing that you’re not getting 8 hours, because that’s what’s recommended, 8 hours, let’s say. And by the way—we talk about this every time—you cannot recommend, let’s say, population averages prescriptively to individuals. You can’t look at a group of a hundred people and say, “OK, well, the average was 8 hours; therefore, you need 8,” because you could need more or less.

Chris Kresser: Mm-hmm.

Dan Pardi: You have your own individual sleep need. Some people sleep more, some people sleep less.

Chris Kresser: And we have a great article guest post by you on my blog that will help you determine how much sleep you need. I think if you search for “Chris Kresser, Dan Pardi,” that should show up.

Dan Pardi: Yeah. Thanks for giving me that opportunity to write that because, like I said, it is a question I get very frequently, and it’s nice to lay out the different factors because the amount that you need can depend on different things, depending on if you’re fighting an infection, if you’ve been playing sports.

Also, “How much sleep do you need—” should be followed by “—for what?” You might perform perfectly well and not have any untoward health side effects from getting a little bit less sleep, but if you’re trying to optimize cognition and information processing and memory and things like that, you might actually need to get more sleep. And the way to do that is to then test the amount of sleep that you’re getting and judge it by how well you think you’re performing, how alert you are, and how sharp you feel the next day. That’s the best way to kind of assess that, and that’s called “sleep satisfaction.” It’s how satisfied are you by the sleep that you’re getting. If you feel kind of a persistent sleepiness, you don’t feel very sharp, then maybe you need more and you should experiment with that.

What the Study Did Not Tell Us

Chris Kresser: Yeah. OK. So what this study hasn’t told us—again, in contrast to what some popular media stories have suggested—is that it’s normal for humans to sleep—or to be in bed, let’s say—for 5-1/2 or 6 hours a night, which is, I think, how it’s been interpreted in some cases.

Dan Pardi: Yeah.

Chris Kresser: But what new information do you think it has highlighted? Or if not new, just interesting angles? The importance of temperature, maybe, in the room that has become a little bit more apparent with this study?

Dan Pardi: Yeah. I didn’t fully complete my last thoughts, and that’s one of them. If you worry too much about getting 8 hours of sleep, let’s say you’re tracking it and you notice you’re in bed for 8 but you’re getting 6, don’t worry. That’s not uncommon. A lot of these findings are not actually inconsistent with sleep findings from the lab. You’ll bring somebody in the lab, they’ll be there for 8 hours, but they’ll sleep for 6 hours and 45 minutes. There’s definitely a distinction between sleep period, which is the in-bed duration, the time that you’re in bed, and then the amount of sleep that you’re getting. Those are two ways to kind of distinguish them, and they’re important.

The other finding, which I thought was interesting, is they comment that light exposure did not have a big impact on sleep time. For me, that wasn’t too much of a surprise because their environment is consistent.

Chris Kresser: Right.

Dan Pardi: It has more of an effect on our life because our environment is very inconsistent. Our lighting environment is as if you were to take one of these groups, let’s say, the San, and you’d move them over several different time zones and you’d plop them down one night, and the next night you’d move them back, and the next night you’d move them back, and the next night you’d move them back.

Chris Kresser: Right.

Dan Pardi: The repetivity of that change is really what we’re inducing with the types of light that we’re getting when we are up late one night watching television and go to bed early the next. That high variability in light exposure is then going to have an effect on the timing of our circadian rhythms.

Chris Kresser: I also can’t help wondering… I know for myself if I look at an iPad or something like that without my orange glasses on, blue-light-filtering glasses on, late at night, it definitely does something to me and makes it harder for me to get to sleep, and I don’t sleep as well that night.

Dan Pardi: Yeah.

Chris Kresser: And maybe the exposure to blue light from an electronic device that’s a couple of feet away from your eyes is different than the light/dark stimulation that they were getting in that ancestral environment.

Dan Pardi: Yeah, absolutely. Every time that you half the distance of a light source to the eyes, so for example, if you’re holding an iPad out 2 feet and you cut it to 1 foot, you quadruple the intensity of the light exposure because more of those photons are going straight into the eye. And if you think about where we tend to hold our iPads or phones if we’re lying down in bed, they’re right up to our face.

Chris Kresser: Yeah.

Dan Pardi: And so even though they’re not emitting very strong light in terms of lux units, which is the light intensity measurement, it is intense because it is going into our eye. There was work out of Chuck Czeisler’s lab recently at Harvard, who’s kind of considered the grandfather of circadian biology—one of the—that they had a study where they were looking at e-readers in your face at night, and they found that there was a significant impact of those sorts of devices on circadian timing, so it would cause a shift.

Chris Kresser: That’s so interesting. I know, like, early versions of the Kindle were non-backlit, right?

Dan Pardi: Yeah.

Chris Kresser: And then, I think, pretty much all Kindles that you can buy… I’m not sure about the other devices because I’m not as familiar with them, but I’m pretty sure all Kindles now are backlit.

Dan Pardi: Yeah.

Chris Kresser: So what should people be doing if they’re reading a Kindle at night when it’s dark? Is it better to turn down the backlighting as much as possible and use room light instead because it’s warmer light, wear blue-light-filtering glasses when they’re reading, or some combination of the above?

Dan Pardi: Yeah. I’d like to add, though, that my mentor, Jamie Zeitzer, who did his PhD under Chuck Czeisler, he wrote a commentary on top of that paper that I just mentioned, and he said that while the results are true—he didn’t question the results—he did question the relativeness of the environment they kept people in. They kept people in very dim, dark environments across the day, and that would basically heighten sensitivity to light exposure at night.

Chris Kresser: Ahh, interesting.

Dan Pardi: Yeah. That’s a really important point.

Chris Kresser: Yeah. I wonder why they did that.

Dan Pardi: Well, I think a lot of times studies are designed to look at the capacity of a system, not necessarily its sensitivity. They kind of want to see if they can get an effect under the best-case scenario.

Chris Kresser: Right.

Dan Pardi: And if you can, then you might kind of work to see how ecologically relevant your findings can be, so you change the conditions to make them more naturalistic. That’s a pretty common way to do it. You first try to see if an effect exists at all, because if not under the best conditions, maybe it’s not worth exploring further.

Chris Kresser: Right. Because one of the recommendations we often make, too, is for people to get bright light exposure during the day—

Dan Pardi: That’s right.

Chris Kresser: —which has some effect on regulating the rhythm, and it’s interesting to think about it from that perspective, too. If you get that exposure to brighter light, then you’re maybe less sensitive to the light you might be exposed to later in the evening when the sun is down.

Dan Pardi: That’s right. That’s why I always say get at least a half an hour of bright light exposure outside during the day because that’s going to anchor your circadian rhythm, and it’s going to make you much less sensitive to light exposure that you’re experiencing at night.

Chris Kresser: Mm-hmm.

Dan Pardi: But a lot of people do work inside all day under much less intense indoor light environments, particularly during the winter where it’s raining and cold outside. You’re going to be inside under normal room light, so that chances that artificial light in the evening is going to cause an effect to shift your circadian rhythms is heightened. Yeah, just a good important point to make. It stresses several things: Get outside during the day when you can, at least a half an hour. If you’re going to have a break at work, go outside. If you’re going to exercise, do it wherever you can, but if you can get outside and do it, that’s great as well. There are additional benefits from circadian rhythm alignment. And then in the evening, yeah, just like we were talking about, there’s not just a spectrum of light that will affect the activity of your master clock in the brain, but it’s also light intensity. So you want to then dim all environmental lights, and then if I’m reading anything in bed, I always wear my blue-blocking glasses. It reduces the intensity a little bit, but it will also pull out all the blue light in that spectrum of light, and it’s that blue light that is the strongest at telling the brain that it is day, and that’s what we want to avoid.

Chris Kresser: I just want to tell everyone that Dan has the fanciest, most stylish blue-light-blocking glasses that I’ve ever seen.

Dan Pardi: Thank you.

Chris Kresser: You have to look good when you’re blocking that blue light.

Dan Pardi: Right?!

Chris Kresser: It doesn’t matter if you’re alone by yourself in a dark room. You never know what’s going to happen.

Dan Pardi: I do it for my wife, you know?

Chris Kresser: It’s good, it’s good. No, as we speak, I’m actually wearing some yellow-tinted glasses. I don’t think they block out much blue light, but they’re glasses made for gamers.

Dan Pardi: Yeah.

Chris Kresser: I just find that they reduce my eyestrain during the day when I’m looking at the computer a lot.

Dan Pardi: Yeah.

Chris Kresser: So I’ll wear these intermittently. And I’m a little bit embarrassed to say this, but I have to say that I’ve been going with the BluBlockers at night.

Dan Pardi: Yeah!

Chris Kresser: I remember the QVC ads when we were growing up, BluBlockers, and of course, I never knew what they were until I learned more about this stuff, that they were actually blocking blue light, and I think they claim to block almost a hundred percent. I don’t know if that’s ever been verified, but I’ll tell you that I’ve tried, now, three or four different brands or types of blue-light-blocking glasses, and I find that the BluBlockers—I have their wraparounds, and they have a panel as part of the wraparound that’s orange also, so it pretty much covers the whole eye area, and I notice a big difference just a few minutes after I put them on at night.

Dan Pardi: They do block a hundred percent of blue light, and the Gunnar yellow-tinted cut the blue light in about half. What’s interesting is that cutting some blue light during the day can actually make people feel more calm because, again, blue light is alerting. So some people perform better when they use some blue light blocking during the day at the office because it makes them feel more calm, and then that makes them feel more productive, which is interesting. It’s only a problem if you’re then not getting outside to get adequate daylight during the day.

Chris Kresser: Right.

Dan Pardi: So if you’re going to do that, you have to get outside, for sure.

Chris Kresser: Yeah. I’ve made a point now when I go outside not to wear sunglasses typically, unless I’m going to be outside for a while or I’m at the beach or something like that. Even then, I’ll spend the first hour or something without sunglasses.

Dan Pardi: Yeah.

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Sleep Recommendations While Traveling

Chris Kresser: Let’s talk just briefly, since we’re finishing up here. I’m going to the UK on Saturday, and I’m gone for a couple of weeks, and Dan has helped me with my strategy for traveling because I want to try to time shift my rhythm as much as possible beforehand so I can ease the transition into this timezone which is 8 hours ahead. I have my glasses, and I have my melatonin. So tell everyone what you advise regarding melatonin for me and why. And then we didn’t talk about how I could use my glasses possibly to help with that shift, so let’s do that too, because I know a lot of people listening to this do a lot of traveling as well, across timezones.

Dan Pardi: Yeah, I get it a lot, so let’s think how melatonin is usually taken supplementally. People take it before bed to induce sleep, and the effects of melatonin are pretty weak as a sleep inducer—but they’re there. Part of the effect of aiding sleep initiation is placebo. If you think it’s working, then you’re more likely to really relax and help you go to sleep, and if there’s even just a little bit of an effect and you think that you’re taking it for a specific reason, it’s going to augment the placebo effect. That’s how most people take it.

Now let’s look at your case, what you’re doing. You’re going to be taking melatonin in a small dose, 0.5 mg to 1 mg, to adjust your circadian rhythm by up to 3 hours a day. That’s kind of the maximal amount that you can shift your rhythm. And you’re going to do that ahead of time, several days ahead of time, so that when you arrive in the UK, you’re not going to have to adjust 9 hours, but you might be in a place where you only have to adjust 3, 4, or 5, so you at least cut it in half or more. It depends on how much you try to adjust between now and then.

Chris Kresser: Mm-hmm.

Dan Pardi: I always save a little bit of adjusting for when I arrive just because it’s easier than trying to fully adjust while I’m here.

Chris Kresser: Right, because then you could run the risk of disrupting your schedule where you are, right?

Dan Pardi: Yeah, exactly. That just is impractical for a lot of people. So what I tend to try to do, in your case, is I look at, when is it getting dark where I’m going, and then what time is that here where I am? And at that time, here where I am, I will then start to take melatonin daily three to four days out before I leave. So that might be noon or 2 in the afternoon depending on, again, where you’re going. And you just take 0.5 mg, and then I might take 0.5 mg 4 or 5 hours later. What you’re doing when you do that is you’re not necessarily facilitating any sleepiness, but you are telling the brain, you’re starting to initiate the process of phase shifting.

Chris Kresser: Mm-hmm.

Dan Pardi: Now, you also want to try to go to bed earlier the first few days, the days preceding leaving, and then also get up earlier as well, so you’re already shifting before you arrive.

Chris Kresser: Right. So if I wanted to accelerate that, would I consider putting on my BluBlockers a little earlier in the day as well?

Dan Pardi: Yeah, absolutely. So you usually put them on in the evening to block the blue light from artificial light, but in this case, you’d put them on maybe starting at 4 in the afternoon. So you’d have some melatonin earlier than that in supplemental form, wear the BluBlockers starting at 4, and then try to go to bed early and wake up early. That’s a pretty good way to do it.

Chris Kresser: So if I wanted to really take this to the next level, I could also have a bright light when I wake up in the morning. Let’s say, if I wake up before dark, I could have a light machine and get some bright light exposure in my eyes, or would just normal daylight at the normal time be enough?

Dan Pardi: Yeah, you could get bright light exposure early in the morning. That’s another shifter of your circadian rhythm. It’s always a good thing to do. You’re managing light environment across the 24-hour period.

Chris Kresser: Yeah.

Dan Pardi: Yeah, so first thing in the morning getting bright light exposure, and actually that’s another very interesting point to the study by Jerry Siegel. They did measure light exposure, and a lot of these hunter-gatherer communities got a lot of light exposure early in the morning, first thing in the morning.

Chris Kresser: Mm-hmm.

Dan Pardi: Then around noon, when it was hottest, the light intensity of the exposure would dim because they would be temperature regulating under trees when it was really hot. I thought that was very fascinating as well. It could suggest another mechanism for why getting light in the morning is a good idea.

Chris Kresser: Fascinating. Thanks so much for coming back on the show, Dan. I’m sure this will help a lot of people and eliminate a lot of potential misunderstanding from that recent study.

Dan Pardi: Thanks for having me back on the show. Always a pleasure.

Chris Kresser: Great. Take care.

Dan Pardi: All right. Have a good trip to the UK, too!

Chris Kresser: Thanks! I definitely will.

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Join the conversation

  1. I love how in depth this article is and I’ve learned something new! Thank you. There’s a strong mental component at play too. With our overtaxed, chaotic lives (adrenal fatigue referenced above), we could be subconsciously sabotaging our ability to get good sleep if we aren’t giving our mind permission to rest and recuperate. Here’s a simple, bedtime breathing exercise to help. With sleep disorders being so complex, and sleep being so critical, addressing it holistically is the way to go! Sweet dreams everyone. https://www.fitlandiafitness.com/breathe-your-way-to-restful-sleep/

  2. I also think it’s fascinating that our ancestors subsisted on much less sleep than the typical recommendation of 7-8 hours. However, some of the same things that tired them our probably the same esp. physical exercise during the day. I know I sleep more soundly if I have run or played tennis that day. They also were outdoors a lot more than we are now. I also tend to think they had a less comfortable sleeping environment than we do now with our fancy beds and bedrooms. It seems like they had more environmental stress worrying about the weather and surviving wild animals and other natural phenomena than we do now. So, in a way, with our comfortable lives, we have the luxury of sleeping 8 hours nightly.

    • I think you missed a major point of the post. That 7-8 hours of time in bed is not the same as 6 hours of sleep. The study pointed out that, yes, the HG groups only needed 6-6.5 hours of real sleep, but that came within the 7-8 hours of down time.

  3. One of things that gets me about these studies is that they are all of people much close to the equator than I live. In the summer the sun sets up to half 9, so three hours + after that will be midnight, and then the sun starts to rise again from about 5. And at the opposite end the sun will set before 5 and doesn’t rise again until 8 the next morning. And I don’t even live that far north in Europe.

    I know, I read the article – it’s about temperature and not light, but the two are related. It’s difficult to get enough light when it’s dark when you leave for work, dark when you finish work, and in the middle you’re in an office whilst it’s chucking down with rain and overcast. Because that happens a lot in winter here in the UK.

    Anyway, rant over. Because I did find some usefulness in the article. I do understand that there’s a difference between the time spent asleep and the time generally in bed (provided you’re not tossing and turning), which is why I don’t get up as soon as my alarm goes off and I try and block out some time before actually getting into bed. As for those who struggle to get to sleep – audio books. Then you can lie in bed and focus your mind on something so you can at least be restful even if you can’t sleep.

  4. Sleep is definitely one of the biggest pieces to the puzzle in functional medicine.

    The truth is, after you get your circadian rhythm aligned by using light therapy and forest bathing, which I podcast about extensively, you still have to work on the blood sugar and adrenals.

    Many people can’t go to sleep or stay asleep even if they take all these rules into consideration!

    Blood sugar drops in the middle of the night due to a worn out adrenal and blood sugar regulation system, which causes that shot of adrenaline and cortisol that wakes you up with a racing mind/heart!

    Stabilize your blood sugar before bed and you’ll sleep much better.

    Blue blocking glasses help, but we have light receptors on our skin as well..

    • Yes, I believe I suffer from the blood sugar instability. Even with all the talk about energy metabolism in the Paleosphere, I don’t seem to be able to absorb much actionable knowledge. I try to eat my carbs *with* protein and fat, eat a carb-heavy snack before bed (with fat, at least), drink some bone broth before bed. I use the Uvex safety glasses, get plenty of sun, walk a lot, eat prebiotics / probiotics in all shapes and sizes, as recommended.

      I was all set to take advantage of frequent testing of various metabolic and blood sugar markers, here in AZ, through Theranos, but, they got trashed by the Wall Street Journal, and now, I don’t know if that is such a good idea.

      My sleep is not too bad, but, I seem to be dependent on olanzapine (minimal dose, 2.5 mg) to stay asleep through the night. Unfortunately, I was suicidal, and needed to take this drug. My mental health is better, now, but, I wake more, during the night, when I miss my dose.

      • John, a miracle micronutrient that is so deficient, even in paleo diets, is chromium.

        There are specific combinations of glycemic support that I use, but a good adrenal program in addition helps reduce those mood rollercoasters.

        The benzod Rx you are referring to is a GABA agonist, meaning that it down-regulates your natural production.. making it difficult to reduce or remove that from your life.

        Sulfur rich foods such as broccoli can help to support the natural production of GABA, but it will have minimal impact compared to more potent natural GABA supportive nutrients.

        • Thanks Evan.

          My new psychiatrist wants to get me off olanzapine. The dose is down to 2.5mg from 10mg. That went okay. The next step is to start skipping doses on alternate days.

          I’ll be working 60-hour weeks until Christmas, so, leaning on the drugs and supplements more than I’d like. I’ve been wanting to get more brassicas and alliums in my diet to support glutathione levels, so, another reason.

          Thanks Again,

  5. Thank you Chris for discussing this paper with someone who has really looked closely at sleep, light, and temperature. You got into the finer points of the research on circadian rhythm and light that were particularly relevant to all of us. The news media could never have addressed the issues you and Pardi raised in this interview. One could only wish they would point listeners to webpages where the study is being critiqued professionally.

  6. It isn’t rocket science. If you wake up naturally (without an alarm) and you have sufficient energy throughout the day, then you probably got enough sleep. Some days you might need only 6 or 7 hours; other days you might need 9 or 10 hours. Your body will let you know if you’re sleep-deprived. It’s up to us as individuals to pay attention and adjust our lives accordingly.

  7. How much sleep do you need? 7 hours is best but no more as 6 or even 5 hours is better than 8. (where “better”=correlates with lower mortality)


    which says

    “among both women and men, the best survival was experienced by those reporting a usual sleep duration of 7 hours, which was 1 hour less than the modal sleep duration.”


    “Participants who reported sleeping 8 hours or more had distinctly and significantly increased mortality hazard: the longer the reported sleep, the higher the mortality hazard. When reported sleep exceeded 8.5 hours (as occurred among 7.5% of women and 7.7% of men), the added risk associated with long sleep exceeded 15%. Reported sleep had to be less than 3.5 hours among women (as occurred among only 0.1%) or less than 4.5 hours among men (0.7% of men) for the added risk associated with short sleep to exceed 15%.”

    so generally it suggests that 7 hours is perhaps best and even 5 is better than 8 or 8+.

    • Don’t forget that correlation does not equal causation! I haven’t looked at the study referenced, but if it’s just reporting an association between longer sleep duration and higher mortality, it seems more likely to be an effect of confounding, rather than extra sleep actually playing a causative role in higher mortality. People with health problems are more likely to sleep longer, and would also have higher mortality rates, so that could account for part of the association.

      • They controlled for a range of covariates. “A total of 32 covariates were entered simultaneously into the models, including sleep duration, insomnia frequency, and variables reflecting demographic risk factors, habits, health, and medication use, selected by preliminary identification of variables substantially predictive of mortality risk (Table 1).” See the article http://archpsyc.jamanetwork.com/article.aspx?articleid=206050

        Is there any contrary evidence that says 8 or 8+ hours correlates with anything positive? Was that a double blind randomized controlled trial? Probably not. Double blind random etc would be near impossible for this sort of study. The best evidence we have is looking at correlations and controlling for confounding risk factors. This study did that.

        I don’t see any evidence supporting the claim that 8 hours is healthier than 5 or 6, especially for those who naturally wake up after 5 or 6 hours.

  8. Chris, interesting read. I have melatonin, too, and it does help. I just don’t like how controversial it is, with researchers like Ray Peat strongly against it.

    But magnesium and B6 don’t do the trick if I’m stressed. I think that means stress is the culprit more than a lack of my allopathic supplementation.

  9. Amazingly verbose. Lots of talk for content that could be delivered in perhaps a fifth or less of the space. And here is this hilariously fuzzy sentence:
    “But what’s really important to note is that the sleep period—so there’s sleep duration, which is how long you slept, and then there’s the sleep period, which is the time that you were actually sleeping, the period of time that you were sleeping.”
    Let’s see:
    “sleep duration” = “how long you slept”
    “sleep period” = “the time that you were actually sleeping…”

    How about “lying in bed awake before falling asleep” and “sleeping”? Naw. That would be plain English.

    • Agreed James, this is not their best work. Hand waiving galore.

      Trust me, no one who has spent three or four hours tossing and turning calls it “sleep” because they happen to be lying down.

      On the plus side my sleep conforms strongly with the hunter gatherer data.

  10. The part about sleep duration and sleep period confused me:

    “But what’s really important to note is that the sleep period—so there’s sleep duration, which is how long you slept, and then there’s the sleep period, which is the time that you were actually sleeping, the period of time that you were sleeping. That was really average. That was 7 to 8-1/2 hours per night, which is what I recommend.”

    So is sleep duration the total amount of time spent in bed, whereas sleep period is the total amount of time actually spent asleep? The end of the paragraph makes it sound like the sleep period is 7 to 8-1/2 hours each night, whereas the sleep duration was only 5.7 hours to 7.1 hours a night. Shouldn’t it be the other way around?

  11. Chris,
    Thanks for noticing Dan’s super-stylish, blue-light-blocking glasses that are so cool you can wear them to a restaurant in the evening. What’s he wearing and where can I find them? My partner probably wouldn’t take me out in public wearing my current glasses!
    Thanks and keep up the awesome work,

  12. Thanks for the interesting information about ancestral sleeping habits. I thought it was cool that they didn’t turn in at sunset but lit fires and danced for a while. How fun!
    So, there’s natural light from the sun, moon, and apparently lit fires. I aim for getting at least 30 minutes of sunlight daily usually while jogging outside. I am self-employed so it’s relatively easy for me to get outside for a 30-minute jog at mid-day when the sun is stronger than most people who are working in offices. I am fortunate to live by a state park along the Potomac river so enjoy nature while jogging. I encourage my clients to take at least a 15-minute break daily and go for a walk outside. This has so many benefits including Vitamin D and setting circadian rythms.

  13. Just an FYI…You can still purchase a Kindle that is not backlit. It is the Kindle paperwhite, their cheapest version. I do believe you can also purchase readers that allow you to turn the back lighting off.

  14. The need for bright light exposure during the day if you’re spending a lot of time indoors is something I’d heard about, but not taken very seriously in the past. Putting in a little more consideration, though, I definitely see a pattern of having a harder time sleeping when I haven’t spent sufficient time outside. Not to mention of getting extremely tired/sleepy indoors during the day. Tons of fantastic actionable advice here. Thanks Chris and Dan!

  15. I once read a Nevil Shute novel in which the hero, one night, took aspirin to help him sleep. I’ve wondered ever since why aspirin would improve sleep quality. And now, after all these years, an answer: it lowers temperature!