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Let me introduce myself. My name is Mark Sisson. I’m 63 years young. I live and work in Malibu, California. In a past life I was a professional marathoner and triathlete. Now my life goal is to help 100 million people get healthy. I started this blog in 2006 to empower people to take full responsibility for their own health and enjoyment of life by investigating, discussing, and critically rethinking everything we’ve assumed to be true about health and wellness...

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October 19 2015

Dear Mark: Do Hunter-Gatherers Sleep Less Than We Thought?

By Worker Bee 2
43 Comments

An image of a full moon night

For years, we’ve thought that hunter-gatherers slept like babies: long and hard. They’d drift off as the sun dropped, lingering around the ubiquitous campfire only for a short time, sleep a good 8-10 hours, and waking up at first light bright eyed for the next day. For today’s edition of Dear Mark, I’m examining a study that calls these assumptions into question. What if hunter-gatherers don’t actually sleep any more than us? What if the absence of artificial light doesn’t lead to a ten hour session of blissful repose under the stars?

Let’s go:

Hi Mark,

I just saw media coverage of a study on hunter-gatherer sleep habits. According to the reporting, hunter-gatherers don’t actually sleep any more than modern people living in the developed world, despite not having smartphones and other emitters of blue light. Does this mean artificial light isn’t a problem?

Thanks,

Jerry

This is a really cool study. Researchers looked at three groups:

  • The San, out of southern Africa, living in villages 20° south of the equator but retaining their hunter-gatherer ways.
  • The Tsimane, along the Maniqui River in Bolivia 15° south of the equator; they are hunter-horticulturalists.
  • The Hadza, in northern Tanzania 2° south of the equator, the only fully nomadic hunter-gatherers of the three.

None of the groups had access to electricity, electronic devices, or artificial lighting. They certainly didn’t have the latest iPhones. The only light available after dark came from small campfires.

Despite the absence of late night Facebook updates, the groups all slept about the same as modern westerners: six and a half hours a night on average, or between 5.7 and 7.1 hours. They also spent roughly the same amount of time in bed. Sleep onset—when they fell asleep—varied more than sleep offset—when they woke up. Across all three groups people woke up at around the same time, so sleep duration was determined primarily by sleep onset. Most groups stayed up for a few hours after sunset.

Sleep duration may be similar between zero-electricity hunter-gatherers and electricity-addicted westerners, but the researchers found other, major differences in how we sleep:

All groups lived their lives in full exposure to the seasonal and temporal variations in ambient temperatures without access to heating or cooling systems. If it was cold out, they felt it. If it was hot, they had to deal with it. Rather than light, ambient temperature was the primary determinant of sleep onset. People usually stayed up past sunset, often going three hours into the dark, only heading to bed when temperatures fell. In the summer, the mean bedtime was 10:44 pm. In winter, it was 9:16 pm. Since wake time was similar throughout the year, they slept an average of 53 minutes longer in the winter.

Insomnia was almost absent. Neither the San nor the Tsimane even have a word for “insomnia” in their language. When prodded, 5% reported ever having trouble falling asleep and 9% reported problems with sleep duration. And only 1.5-2.5% reported having these sleep issues more than once a year. Meanwhile, 10-30% of people living in industrialized countries report chronic insomnia, and sleep disorders are so widespread in the US that doctors write over 60 million sleeping pill prescriptions each year.

They didn’t nap. Other than a few instances, the majority of San, Hadza, and Tsimane rarely napped. Folks living in industrial cultures tend to experience a mid-afternoon dip in energy, and naps are an effective way to recharge and even improve attentional capacity. Problem is we don’t get the chance to take them very often.

They usually woke right before sunrise. Contrary to industrial societies, where waking occurs after sunrise and people are likely to sleep in as long as they can (which usually isn’t very long), the majority of the hunter-gatherers’ only slept when it was dark out.

They got the majority of their light exposure in the morning. They tended to avoid a lot of light during the afternoon, probably because it coincided with sweltering tropical temperatures. This squares with clinical research finding that morning light exposure is effective in treating sleep and mood disorders. And since most people living in industrialized countries sleep past sunrise and remain indoors for those critical morning hours, they’re missing out on what may be a vital piece of hunter-gatherer sleep hygiene: maximal light exposure in the morning.

Stress increases sleep requirements (PDF). These people aren’t working 14 hour days. Heck, they may be working 14 hour weeks. They aren’t trying to convince their kids to complete their 3.5 hours of homework a night or stewing over a disappointing sex life. In short, the hunter-gatherers haven’t erected the manmade stressors that pervade our lives and make sleep such a necessary yet fleeting delicacy. This may explain why we need (but usually don’t get) naps and the Hadza, San, and Tsimane do not. Unlike 6.5 hours-a-night-sleeping people from industrialized nations, the people in this study were remarkably free of metabolic syndrome, diabetes, overweight/obesity, and all the other health conditions usually associated with inadequate sleep. They’re free to sleep more than 6.5 hours if they want or need it. They just don’t do it. 6.5 hours is, clearly, perfectly adequate for them. We want to sleep more than the 6 or 7 hours we’re allotted, but we often can’t do it.

The fact remains that artificial light negatively affects sleep in modern populations. I’ve covered this before, and the evidence is quite clear. This study doesn’t change that.

Ambient temperature is probably more important for sleep than we previously thought. We simply don’t experience the wide variation in ambient temperatures occurring, mostly because we’re no longer outdoors much. Plus, when we’re inside, we’ve got the heat going (if it’s cold) or the AC on (if it’s hot). We have the luxury of remaining at the same ambient temperature for our entire lives if we want. And boy do we want it.

For sleep to occur, body temperature must drop. If the ambient temperature is high, our body takes longer and works harder to drop temperature. If the ambient temperature is lower, it’s easier for our body to lower its temperature and sleep to commence. People with heated homes take longer and work harder to reach the necessary body temperature for sleep.

This is a great paper. I’m not sure it absolves our smartphones in the bedroom habit, though.

What’s your take on the paper, folks? What else do you have to add?

Thanks for reading, everyone. Take care and have a great rest of the week.

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43 thoughts on “Dear Mark: Do Hunter-Gatherers Sleep Less Than We Thought?”

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  1. I’m not surprised by the temperature results. I have discovered this to be a prime driver of sleep quality in myself. The bedroom temperature needs to be at least 68 deg F (better if lower), else I sleep fitfully, wake up sweating, and can’t get back to sleep.

  2. I love the sleep element of the primal blueprint and make sure I get 8 hours every night and more on the weekends including naps. It has really improved my mental, physical and emotional well-being.

  3. What occurred to me when I first read about this study is that it says nothing of the quality of sleep. I wonder if there’s something about the hunter gatherer lifestyle that leads to more deep sleep. I know that I feel about a hundred times better getting 5 hours of good quality deep sleep than I do getting 8+ hours without deep sleep (I monitor my sleep, so I have some sense of how much deep sleep I got). Last night, for instance, I got only 5.5 hours, woke up nearly 2 hours ahead of my alarm, and couldn’t back to sleep. But I feel fine because it was almost all deep sleep.

    1. Yes, I wondered that too the phrase ‘restorative sleep’ sprung to mind.

      I’m in chronic sleep debt at the moment due a number of life stressors. I’ve noticed this makes me super sensitive to the quality of the sleep I do get. 3 hours of deep sleep without waking being far better than 5 hours accumulated in fits and starts over the night.

  4. I was going to point out the insomnia thing too. They may have slept the same amount of time that we do but they surely slept a lot better than most of us do, for a multitude of reasons.

  5. This is a relief to me, my usual sleep is only up to 7 hours but usually around 5.5 to 6 hours, less or none if there are stressors that need my attention – thankfully that’s not very often.
    I will wake up from being too cold if the temp gets below 68, I sleep the best at about 71 but I can sleep just fine above 80, just less covers. Perhaps I should move closer to the equator.

  6. My first thought, aside from quality of sleep, was location. They note a seasonal variation but none of the subjects had particularly pronounced seasons. The San had the longest night with near to 13 hours in winter. This doesn’t compare to 16+ hours of darkness for people living further from the equator.

    And the temperatures are hardly comparable either. If it’s so critical, then surely spending winter with highs below freezing and lows even colder would influence sleep.

  7. The temperature issues make sense. I know I struggle to sleep well if the temperature is above 70. I do wonder about the stress issue. I think hunter/ gatherers live a pretty stressful life. I know if I lived under those circumstances, I would be constantly stressed out about where my next meal would come from. I remember when I hunted for food and was pretty stressed about getting the deer for the freezer. Many sleepless nights worrying about that.

  8. If my house wasn’t heated in the winter, we would be incredibly uncomfortable to the point of not being able to sleep. Plus, there’s the issue with all the liquids in the house freezing…
    But keeping the thermostat set around 66f when the high temperature for the day is les than or equal to that number works fine and saves money. In the summer, we keep it set to 75F – still pretty warm by most peoples’ standards, but we’re mostly outside where its hot. 75 feels cool after a few hours in the sun.

  9. I loved this study. We clearly did this to ourselves.

    Their diet is clearly a major part of it. I just came off a week-long break from my everyday diet and noticed how crippled I felt by little things. They only need 6.5 hours of sleep because their bodies are humming along optimally.

    Temp was no surprise either. I don’t keep my house about the same temp all year; it’s usually about 20 degrees variable. In the summer, I can’t sleep if it’s above 75–sweating while trying to sleep means bad quality of sleep. But in the winter, I usually keep my house around 55 or 60, but I’ll turn it up if I expect company.

    Finally, light! I have new neighbors who insist on illuminating 100% of their backyard and 75% of mine, and my sleep has been terrible for the 4 months they’ve lived there. All things equal, light destroys your sleep quality.

    1. Invest in some properly fitted blackout blinds/curtains. Does a lot for my sleep quality (I live almost on a major suburban crossroads)

    2. We might have the same neighbor! LOL You know those retractable awnings with Sunbrella fabric? You can have them go straight down (vertical) over your window. In our bedroom on one wall, we have that (remote controlled) AND we have curtains with a blackout backing. On the other wall, have two smaller side windows and we’ve got blackout accordion shades (they are white, they come in colors) AND Roman shades.

      If circumstances permit you to talk with your neighbor, one option for them is motion-detector lighting.

      As an aside, I’m in Los Angeles and there is so much artificial light, our sky is brown at night. So sad.

  10. If it is too cold I cannot get to sleep. I need to feel “toasty” to sleep. If it’s too hot I don’t have any AC in my house and it’s hard to sleep. I can’t cool off even with no blankets or sheets on me. And then I’m a sitting duck for mosquitoes. Needless to say this Southern Californian had a difficult summer. Is it over yet?

    1. 🙂

      i hate being cold

      in winter, i can tolerate lower temp. during the day (cause i’m awake & moving)

      i turn thethermostat up during the bedtime so i can sleep
      68F is too cold to fall asleep (feet cold). or i’d need a thermal blanket.

      interesting thing about their lack of nap tho

    2. I can’t get to sleep if I’m too cold either – my legs and feet just ache. In the winter I usually have flannel sheets, a down comforter and 2-3 quilts on top of me. Even then I often need to resort to a hot water bottle to warm up my feet enough to fall asleep. It takes so long to warm up the bed with just body heat that my muscles start cramping.

      1. On the temperature thing, I’d love to see a difference between a cold room temperature with many or heated blankets, and a warmer room with fewer blankets.

        In the cold room, insulated bed scenario you are still getting the cold air but the body is warm. As such it might help keep he internal temperature cool while keeping the skin (where we have sensors) warm. My wife, before we moved to TX, was always of the cold air + warm bed philosophy. I’ve always been a “I need more than a sheet” to feel remotely “sleep-settled” and used to sleep on a cool waterbed. But I, another lifelong insomniac, have noticed a distinct improvement when the temp is 65-68 in the room over even 72 in the room.

        Camping in the hills almost always means no sleep problems for me either. The temperature variation is usually there as well. Now that I think of it we also usually stay up a few hours after sunset enjoying the firelight.

  11. The temperature thing strikes me as very interesting… is this the reason I wake up multiple times in the night? Because I’m too hot? I do get enough sleep – I often feel great – but the duration it takes me is roughly 10 hours. Mildly annoying.

    Unfortunately, I live in a condo and the place I sleep is an inside room that always seems hotter than the rest of the place. Maybe I should stop using blankets…

  12. This article makes me feel so much better about my sleep! I can usually get 6-7 hours straight, and feel fine. I simply cant fall asleep again once I have had that amount of sleep. I was feeling a bit concerned when I read on other blogs that “healing” requires “lots” of sleep – generally more than I get! The moral:
    I should just pay attention to how I feel, and not worry what other people’s sleep needs are….

  13. I’m glad they’re doing what works for them. I’ll continue getting around 9 hours daily.

  14. I have an opposite problem of not ever being cold enough when I sleep! I prefer 55 degrees for sleeping, but live in a well-insulated 3rd floor apartment. I can’t open the window to cool it down because then I end up with noise — traffic, newspaper guy at 4 am, etc.

    Winter cannot come soon enough!

  15. it is interesting to review the many changes in the various hunter gatherer populations that remain. For example, there are many studies of the San or Ju\Wasai as they are known. Those in the 1960s record a very different life style to today. While these hunter gatherers are the remants they are also all we have to study and research. However, conclusions need to be cautiously drawn. In the early 1960’s the San appeared to experience diurnal sleep patterns – I’m not sure this is the case now in more recent studies where they seem to sleep through. This is unfortunate for the San who are losing there way of life and doubly so for us as they appear to be the remants of the culture that was out on the savannah for a long time before some humans left Africa and headed for Europe and asia. Enuff said

  16. Something that isn’t mentioned is how and if the amount of sleep required is related to the amount of mental stimulation, the amount of concentration and learning and brain drain. Thinking back to the post on napping, and all those very intellectual people who were in the habit of taking frequent naps, could it not be that the brain itself needs rest and ripose, and more so if it is constantly being put through a workout? Is it not so much that hunter-gathers are not working 8 -10 hours a days or confronting modern life stressors, but rather that they are not writing the Encyclopedia Brittanica?

    There’s more. Sleep is not just about physical and physiological recuperation. It’s also about balancing the psyche, allowing the concious mind to depart and the unconscious to rise to the surface. They say that a good, deep 1 hour practice of Yoga Nidra, where partecipants reach and remain on the border of the conscious and the unconscious states, is equivalent to many hours of normal sleep. Is it not the case that hunter gatherers are much, much more in relationship with the unconscious, that there is not the hard dualist division between sleep-and-wake, but rather a much softer blending of the boundaries? Thinking of pre-colonised Aboriginal Australians, with their songlines and dreamtime culture, I would imagine that living with and being with the natural world to such an extent would allow the intuitive-subconscious-unconscious to be as present in the waking state as the conscious mind itself. We need to make time to sit and contemplate and meditate to balance the psyche: for them, it was just a part of life. I think this balance (or lack of) between consciousness and unconsciousness must impact on the amount of sleep required.

    Just thinking.

    1. This fits with what I remember of Daniel Everett’s description of the Piraha people. They’re not religious about getting 8 hours of sleep (I forget exactly how ‘bad’ their sleeping habits are), and they don’t think dreams are less real than the ‘awake world’.

      1. I’ve read several books by Everett. He describes their sleep habits in detail.

        They don’t sleep straight through the night. There are always Piraha awake and talking. They do lay down at night, but it is as much of a social experience as a sleep experience. He explains that they stay awake because of predators, such that someone is awake to keep an eye on those sleeping. It seems that they mostly sleep when they fee tired, as they eat when their hungry. This also includes naps during the daytime.

        I doubt the Piraha are unusual. Researchers looked at historical documents. They determined that it was common for Europeans in earlier centuries to wake up in the middle of the night, stay awake for a few hours, and then fall back asleep. This in-between time was when they would do simple work like darning their socks and probably talking was involved.

    2. Angie – all very good points. I posted with a similar question about mental stimulation, before reading your comment.

      In addition to the requirement for additional recovery after mentally demanding tasks, one thing I mentioned was my reduced need for sleep to function on days that are not mentally demanding.

      In other words, on days preceding work, I find I need 8-9 hours of sleep. Yet, on days preceding weekends, vacation, etc., I find I do great (and feel better) on 6-7 hours of sleep. If I were to sit down and try to do work on one of these “off” days, I’d have trouble concentrating, feel sleepy and have an urge for a nap. Yet, when I don’t try to do work on these days, I feel great and energized.

      Perhaps mental stimulation doesn’t only require additional sleep, but the conscious feeling of tiredness is sparked by a need to be mentally aware and focused.

    3. Also physical exertion, exercise, even a long day out bushwalking, and when you get back, you’ll sleep like a baby, guaranteed.

  17. No AC, usually don’t need it here by Puget Sound, but fans are nice on summer nights to move the air and provide white noise to muffle outside noises when the windows are open. I need at least a sheet over me (protection from the monster under the bed?). I’ve been able to delay adding an extra blanket this fall by putting on a knit cap when I wake up cold. Admittedly, a little heat in the bedroom helps. The hat slides over my eyes in the night and keeps out the morning sun, a bonus.

  18. I love sleeping in a cold room–if I have lots of blankets to snuggle under. I like having that weight on me.

    I’d love to see a study of the sleep habits of new mothers in more primal cultures. My 3-week old is doing a pretty good sleeping at night (the more I wear her during the day the better she sleeps at night–strange but true), but not all mine have, and I’d love to see how cultures like the ones studied handle these early weeks/months/years.

  19. mmmm…14 hour weeks…that just jumped out at me…
    But seriously, I agree with others here that there must be a relationship between how demanding one’s days are and how much sleep one needs. Ask top athletes what they sleep, or young mothers what they would like to sleep (if they weren’t up nursing in the night!), and you’ll probably hear 9-10 hours. Ask a retired guy like my dad who doesn’t push himself hard, and 7 is fine.

  20. Mark – as always, you make great points in your post. Thank you for that.

    Do you know if the researchers also adopted their subjects’ lifestyle while they were studying them? If yes, did their sleep schedule change? If not, do you know of any “Westerners” who have lived with hunter-gatherers for a significant amount of time, and how their sleep patterns / energy levels changed? I can’t help but think of the famous study, in which participants slept in a cave, caught up on sleep debt for about 2 weeks (10-12 hours of sleep per night), then normalized at about 7-8 hours.

    I ask because of something that came to mind from personal experience: I do perfectly fine with ~6 hours of sleep per night, *when I’m not working*. When I force myself to sit in front of a computer and do the same routine (work), I *need* 8-9 hours of sleep (and ideally, some caffeine!). However, on weekends, holiday breaks and vacations, I can get by with 6-7 hours, feel energized, content and don’t have an urge for a nap. I also tend to be outdoors more on these occasions. Is it possible that our modern requirement for constant attention not only leads to a requirement for more sleep, but more importantly, *makes us more keenly aware of our lack of sleep?*

    1. Chris, I can say that whenever I’ve been out in the woods (so to speak) whether it be recreational camping or military deployment, I’ve nearly instantly gone from insomniac to sleeps w/o issue. I’ve always considered it odd. Perhaps not so odd anymore.

  21. Can anyone comment on hunter-gatherers and caves? I can’t help but imagine a large percentage of early humans sleeping in caves, for protection from predatory species. Does anyone know if this is the case, and a rough percentage of those who did?

    I ask because a cave would change a lot of the factors that we believe to be important for sleep hygiene. Temperatures are lower than outdoors (enabling the cave dweller to *decide* when they go to sleep, not mother nature) AND more constant (allowing for longer periods). Sunlight would not hit you directly, so your eyes’, brain’s and skin’s photosensitive cells wouldn’t be impacted. Moon and starlight would also not hit you at night, so it would be even more similar to our blackout curtains (does anyone know the spectrum and lumens of the nighttime sky on a full moon and crescent?).

    Also, recent studies indicate that our brain is constantly listening for sound while we’re sleeping – even when we’re in a deep sleep. Being in a cave may reduce a fair amount of that noise, and put the sleeper at ease.

    I would suspect that cave dwellers would sleep for longer time periods than the hunter-gatherers in this study, but this is only a hypothesis, and I don’t know what portion of the population of early humans slept in caves.

    1. I’ve been thinking about the cave situation myself lately. Caves and other forms of shelter can actually end up removing natural light from the equation of circadian rhythms; did our ancestors actually wake up at sunrise? If so, how did they know what time that would be? These studies claim that they would wake up at the same time every morning, but without the influence of sunlight it’s hard to distinguish how they actually slept…

      I do find it really interesting that they stayed up for several hours after sunset, as well. I’d have thought that the onset of darkness (and thus melatonin) would result in a shorter window of time before falling asleep, although being sleep-deprived is a key factor in time taken to fall asleep (which they were not).

  22. If I go to sleep cold, I’ve found I don’t sleep well at all and then experience fatigue and mild cold/flu-like symptoms. Unfortunately, I’m a cold person so to prevent this I have to wrap up warm to feel warm enough to sleep well – then I wake up dehydrated and groggy! There is no winning!

    Does anyone know of any articles on how to improve body temperature regulation? I live in the UK so not the warmest or the coldest place, yet I always seem to be sweltering or like ice (usually the latter).

  23. Ever since I cut back my sleep to about 6 hours, I’ve done so much better!
    For years I tried getting the prescribed 8 hours, and always woke groggy and cranky. I tried getting 9 hours of sleep a night, then 10, it was never enough. There was a month long period where for whatever reason, I was in bed shortly before and falling asleep pretty much exactly at midnight. I was waking up at 6 am, almost on the dot, every single morning. I kept going back to sleep, desperate for that last hour or two. I decided to just get up when I woke up, and see how I felt.
    And I felt great! I mean, I felt incredible! I had energy, my mood improved, I started wanting to work out; my entire day was just better when I did this.
    Five years now I’ve been doing this routine, midnight to 6am, and I highly recommend it.
    I also typically start my morning workout outside, just before sunrise, then working the garden, so I’m exposed to that early morning sunlight you mention.

  24. Highly interesting. I realize I often wake up in the middle of the night feeling too warm. Whenever I put a fan on in the room it helps me sleep, so temperature seems to be a key here. I think Im just not that acostumed to having the windows open entirely throgout the night. Will have to test this. Cheers!
    /Erik