The topic of sleep seems to be on my mind more than usual every time Ed goes on vacation, so this story immediately caught my attention. How much sleep is actually “normal” for a relatively healthy adult human being? I’m guessing that many of you have heard that eight hours is the ideal amount per night but it’s a rare day when I can sleep that long even if I’ve got nothing driving me out of bed in the morning. And what about naps? (I’m definitely in the pro-nap camp these days.)

Some hot shot scientists seem to have come up with a way to test the theory. Most of us are affected by things like artificial light after the sun goes down, alarms, electronic devices and all manner of stimuli which throw off what might otherwise be our regular sleep cycles. With that in mind, they located a few groups of remote, hunter-gatherers, specifically the Hadza of Tanzania, the San of Namibia, and the Tsimane of Bolivia. They don’t use any form of electronics or artificial light besides campfires or torches. How much do they sleep? Not as much as you might have guessed. (Washington Post)

Using Actiwatch-2 devices (a kind of a souped-up, medical-grade Fitbit for sleep), researchers recorded the sleeping habits of 94 of these tribespeople and ended up collecting data representing 1,165 days.

What they found was a striking uniformity in their sleep patterns despite their geographic isolation. On average, all three groups sleep a little less than 6.5 hours a night, do not take naps and don’t go to sleep when it gets dark. Like many of us, the Hazda, San and Tsimane spent more time in bed — from 6.9 to 8.5 hours — than they do actually sleeping. That computes to a sleep efficiency of between 81 to 86 percent — which is very similar to today’s industrial populations.

The findings on naps were equally counterintuitive.

The data from the San in Namibia, for instance, shows no afternoon naps during 210 days of recording in the winter and 10 naps in 364 days in the summer. The findings were similar for the other two tribes, suggesting that napping isn’t really a common thing among hunter-gatherers, either.

Maybe we’re not built to sleep eight hours every night. But we definitely need to get a solid block of deep sleep. Some of the most current data indicates that solid blocks of sleep are needed to regenerate hormones, promote growth in children and restore brain function to “normal” levels for the next day. Prolonged lack of sleep leads to a variety of physical maladies before very long.

Other studies show that we build up a chemical called adenosine in our systems while we’re awake and it drives us toward shutting down for brain maintenance. We need to sleep to get rid of it. And further, at least if the lab rats are any indication, if you lose too much sleep you’ll eventually just die. (Rats who normally live one to two years, when allowed no solid blocks of deep sleep, died in as little as five weeks.)

There’s some good reading at the links if you’d like to learn more. My only question is how accurate the data is that they derived from the hunter-gatherers. The mere act of observing anything tends to alter the subject being observed, and if you took a group of people who were that remote and isolated from the modern world, strapping Fitbits on all of them seems like it might have affected the study. Maybe they normally would have slept eight hours but they spent the extra 1.5 hours every night checking their new email accounts.

Food for thought. Or possibly sleep.