Why the ‘preindustrial societies sleep study’ may not apply to you

The recently published preindustrial societies sleep study has received quite a bit of media coverage recently, and for good reason.

This interesting study showed those living today in some of the world’s few remaining preindustrial societies — meaning hunter gatherer and subsistence farming groups without access to electric lighting or heated and cooled living spaces — generally sleep only about 6 to 7 hours per night, with very little evidence of insomnia or other negative consequences of sleep deprivation.  These results have led some sleep specialists to question if the often recommended sleep ranges of 7 to 9 hours might be considerably too long.

But you might want to hold off on concluding what works for these primitive cultures might also be right for you, for a couple of reasons — one having to do with this study’s reliability, and the second concerning its validity.

Regarding reliability, consider the researchers used actigraphs to measure sleep, specifically the Phillips Actiwatch 2 wristwatch style device.  Unlike polysomnography (PSG) — the gold standard for sleep measurement that monitors brain wave activity, heart and respiration rates, among other metabolic measurements — actigraphs specifically measure gross motor movements.  Actigraphy assumes lack of motion means sleep.  However, as most insomniacs can attest, there often can be a lack of motion in bed, along with a lack of sleep as well.

Phillips does provide some validation documentation supporting their device’s reliability compared to PSG, so let’s give them the benefit of the doubt and assume the measurements of sleep duration in this study were reasonably accurate.

That still leaves the question of validity.

The study appears to have a latitude bias, meaning distance from the equator.  In this case, all of the subjects were located in the subtropics, either very close to the equator or within about 20 degrees of it.  This is significant because the amount of daylight on any given day is directly related to latitude.  Those living above or below the tropics will experience much longer nights during the winter, and much shorter nights during the summer.

For instance, those living near 40 degrees latitude — that includes New York City, Denver, Beijing, and most of New Zealand — experience at winter solstice a night that is about 24% longer than those living at Quito, Ecuador, which is very near the equator.  That translates to about 3 more hours of night.  Those living at 50 degrees latitude — that’s the U.K., Germany, most of Canada and Russia, and all of Scandinavia — experience a night that is at least 4.5 hours longer at the winter solstice.

So in this study, the researchers found people living in these few remaining preindustrial societies near the equator only spent about 7 to 8.5 hours in bed — but would that still be true if nights were 4 or 5 hours longer?

How long did the preindustrial Inuit people of the Arctic regions spend in bed during winter nights, when the sun barely comes up at all, and nights can last close to 24 hours?

These questions aren’t answered, but it certainly seems reasonable to think the native Inuit a century ago would spend quite a bit longer than 8 hours in bed during winter.

In fact there are substantial historical records showing that people living at the higher latitudes in western preindustrial societies would spend 10, 11, 12 or more hours in bed during winter.  These widespread historical records show normal sleep a century or more ago during the winter was more biphasic, with two blocks of sleep separated by two or more hours of wakefulness in the middle of the night.

These documents show back then people might sleep for four solid hours, wake up for two or more hours, then fall back asleep again until morning.  The wakeful period in the middle of the night was called “the watch” or watchful sleep period.  This was generally described as a period of quietness and peacefulness, almost like a meditative state.

So it may be that sleep duration is conditioned somewhat by latitude, which isn’t controlled in this study.  On the other hand, this research does drive another nail in the coffin of the so-called “myth of 8 hours”.   This refers to the now widely debunked idea that you absolutely must get a minimum of 8 hours of sleep each night to perform at your best.

Just as there is no set diet that somehow works for everyone, neither is there one agreed-upon amount of sleep that magically works for everyone.  The sleep you need is unique to you, and everyone has different sleep requirements.

There are many interrelated factors that determine how much sleep is best for you, including your unique metabolism, which changes as you age.  Your sleep can be affected by your diet, your occupation, the amount of stress you experience on any particular day.  Your sleep can be influenced by the amount of exercise you get, and many psychological factors such as anxiety.

The bottom line?  Just because these equatorial preindustrial societies sleep 6 to 7 hours a night doesn’t mean you should too.  There simply is no one specific number of hours that is the “right” amount everyone should get.

Our philosophy with the Sleep Training System is this:  there is only one number we are concerned about — what’s right for you, and the STS will help you determine that.

Explore posts in the same categories: Health, Insomnia, sleep

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