TOPICS > Science

These hunter-gatherer tribes sleep less than you, and sleep better

October 15, 2015 at 6:25 PM EDT
By studying the habits of three hunter-gatherer groups who live much the way humans have for thousands of years, a team of scientists is challenging conventional wisdom about how much sleep we need. Hari Sreenivasan goes to UCLA to learn more about getting enough rest and to do something he's never done on assignment before: falling asleep while on the job.

HARI SREENIVASAN: But, first, just how much sleep do you really need? There’s been plenty of concern, as people spend more time looking at their screens ever later into the night.

Previous research has shown that a lack of sleep is associated with a series of problems, ranging from lack of concentration to health effects like obesity and heart disease.

But a new study out today finds seven or eight hours a night may not be as essential as we think.

I went to California to learn more.

They are among the last hunter-gatherers in the world, the Hadza of Northern Tanzania, the San of Namibia’s Kalahari Desert, and in the Andean foothills of Bolivia the Chimane.

By studying the sleep habits of these three groups, who still live the way humans have for thousands of years, a team of scientists led by UCLA’s Jerry Siegel is challenging conventional wisdom about how much sleep we need.

JERRY SIEGEL, Director, UCLA Center for Sleep Research: It’s absolutely incorrect to think that the more you sleep, the healthier you’re going to be.

HARI SREENIVASAN: The study, reported today in the journal “Current Biology” says we in the industrialized world sleep as much as our ancestors did.

JERRY SIEGEL: There’s been speculation that humans basically used to sleep when it got dark, which would mean they’d sleep 10, 11, even 12 hours. But it turns out that’s not the case. These groups sleep five, six, seven hours. None of them average over eight hours of sleep.

HARI SREENIVASAN: Just like us, when the sun sets, these people do not go right to sleep.

JERRY SIEGEL: There’s a thin yellow line here that indicates the light level, and you can see also that they remain awake.

HARI SREENIVASAN: In fact, regardless of what time they go to bed, all three groups, on different parts of the planet, wake up exactly when one very specific thing happens. And, no, it’s not the sunrise.

JERRY SIEGEL: They’re sleeping as the temperature falls, and they seem to quite consistently wake up at the lowest point of temperature in the day. So, when the temperature stops falling, that’s when they wake up.

There’s been a lot of emphasis on light and the effects of light, and there’s no question that light affects sleep. But light may have been connected to sleep largely because of its connection to temperature.

HARI SREENIVASAN: Temperature swings are a thing of the past. Now we just have to turn a dial.

The connections between sleep and many things have been thoroughly studied. Thanks to a smartwatch, I have been a student for the past year-and-a-half, trying to figure out ways to get a better night’s rest. Between late-night check-ins at hotel rooms and early-morning flights, I have become a lousy sleeper.
My smartwatch tracks when I’m in deep sleep, light sleep, REM sleep, when I move around, and how many interruptions I have, and it even gives me a score for the night. But there are much more accurate ways to measure sleep in a lab.

So, for the good of the story, I put on a hospital gown and pajamas and got wired up at the UCLA Sleep Disorder Center.

That’s a lot of wires.


JOEL RECTOR, UCLA Sleep Disorder Center: Yes, I believe 32.

HARI SREENIVASAN: Lab manager Joel Rector placed sensors on specific parts of my head to measure electrical activity in my brain, stuck some near my eyes and on my legs to measure even the slightest twitches, and strapped sensors around my chest and stomach to gauge my breaths.

JOEL RECTOR: I’m going to put this over your shoulder.

HARI SREENIVASAN: Doesn’t feel like the most natural way to go to sleep.

And I did something I have never done at work. I tried to fall asleep on the job.

So, just to run through this, all these are measuring my brain waves. This is measuring my breath and oxygen. This is measuring how much I’m moving here and here and on my legs. And this is measuring my oxygen.



JOEL RECTOR: All righty. Well, I will get the lights off.


While I napped, Rector monitored my patterns.

JOEL RECTOR: He’s in stage two sleep, which is what most people are in for the majority of the night. He’s kind of just sleeping quietly.

HARI SREENIVASAN: When I woke up, I had a chat with neuroscientist Alon Avidan, who runs the sleep disorders lab, to tell me what he saw.

DR. ALON AVIDAN, Director, UCLA Sleep Disorder Center: Typically, when we ask someone to fall asleep, we don’t see them fall asleep in less than eight minutes. You fell asleep in less than a minute, which means that…


DR. ALON AVIDAN: … you are probably sleep-deprived.

HARI SREENIVASAN: What can happen if you’re chronically sleep-deprived?

DR. ALON AVIDAN: The data shows that in people who are chronically sleep-deprived, the immune system doesn’t work as well. You’re more prone to develop obesity, diabetes. Cognitive function tends to become depressed.

HARI SREENIVASAN: But what constitutes sleep deprivation?

Max Hirshkowitz is chair of the National Sleep Foundation, and a guest lecturer at Stanford Medical School. He recently convened a panel of experts to recommend how much sleep we should get.

MAX HIRSHKOWITZ, National Sleep Foundation: About seven to nine hours. It’s a range. Now, six may be appropriate under unusual circumstances, but, otherwise, seven to nine, somewhere in there.

HARI SREENIVASAN: There is no shortage of pills that try to deliver those seven to nine hours.

NARRATOR: Sleep better, sleep longer.

NARRATOR: There’s a land of restful sleep. We can help you go there.

HARI SREENIVASAN: And that concerns Siegel.

JERRY SIEGEL: The thing that alarms me is this thought that — and this was the motivation for undertaking the study, to find out if this true — that we used to sleep much more, and that we need to increase our sleep from whatever number we get to be closer to 10, 11 hours of sleep. The data that we have gathered indicates that’s not the case.

HARI SREENIVASAN: In fact, these people Siegel studied average less than six-and-a-half-hours, and they seem fine.

JERRY SIEGEL: In general, the adults are more healthy than those in our society. They may for some reason need less sleep, but there certainly doesn’t seem to be any negative consequence resulting from their sleep pattern.

HARI SREENIVASAN: They also don’t appear tired during the day. They hardly nap and they sleep soundly when they do.

JERRY SIEGEL: One thing we found is that these groups have very little insomnia, maybe at a 10th the incidence we have, and so there’s something different there that’s going on.

HARI SREENIVASAN: That something will take more research to figure out.

So, back to the lab, or, in this case, back to bed.