Friday, October 16, 2015

Hunter-gatherers sleep like me

Anthropologists Gandhi Yetish, Hillard Kaplan and their colleagues just published the results of some experiments that show hunter gathers get much less sleep than the eight hours we supposedly need. In fact, their sleep patterns closely resemble mine, despite the conventional wisdom that my average 6.5 hours per night is too little.  (There’s a nice summary by Anahad O'Connor in a New York Times Blog post)

A long-time fan of Zeo, I have carefully measured my sleep for many years and I know that my lifetime average is pretty close to 6.5 hours. That’s real sleep, measured by a brain wave detector strapped to my head. Like other lazy people, I sometimes lay in bed longer than that, but it’s a rare occasion when my sleep duration is longer than 7 hours, even when I’m loaded with potato starch to grow serotonin-helping bifidobacterium.

Because the new study appears to contradict the rest of conventional scientific wisdom about the importance of 8+ hours of sleep, I read it carefully, along with the data collected to see if I could spot any problems.  So far I think everything adds up:

Plenty of participants:  100 people, spread among male/female at different ages, including some fairly old: 60+

Three separate, unrelated societies: from both Africa and South America, it’s hard to argue these people are somehow related at anything other than being hunter-gatherers.

Week-long observations: You might want a study like this to go on for weeks or years, but I think the duration, from a week to a month per person was just fine. 

Good self-tracking hardware: the anthropologists used the Philips Actiwatch 2, strapped to subjects’ wrists with a tamper-proof hospital band. These are well-studied, medical-grade wearables and although they use actigraphy information, not perfect because it’s based on movements in the night, if anything these devices tend to overestimate the amount of sleep. I skimmed the data from the study and it looks good.

The authors conclude that ambient temperature, not daylight, is the most important signal that tells these hunter-gatherers it’s time to sleep. They note that these people sleep no the ground on skin mats, inside huts or in the outdoors, often covered with lightweight cotton blankets. This isn’t all that different from camping, when I tend if anything to sleep more

Interestingly, when Zeo studied 5000 of their users back in 2011, they found an average sleep time of something closer to 8 hours, with my 6.5 hours falling out of the 95% confidence interval, making me (and the hunter gatherers) real outliers.

Note that although I rarely sleep longer than 6.5 hours, I feel great in the morning and I’m generally alert and feel reasonably fresh all day. Like the hunter-gatherers, I don’t nap and I rarely suffer from insomnia.

I’ll be watching the follow-ups to this research carefully but for now I’ll be much more satisfied that my current level of sleep is just fine.