I had intended on posting about this sleep study when it came out last year but I was derailed. Yesterday I saw an article about it, yet another that took the results of this age-specific study and extrapolated them onto people of all ages. People writing about it are also applying the results to those who live in modern, developed countries, with all the accouterments that implies … climate-controlled homes and offices, artificial light, food in the fridge, drugs (caffeine, alcohol, cigarettes, over-the-counter, pharmaceutical, and street drugs), beds and pillows! … when the data was collected on people who live without these products.
Here’s the study:
Natural Sleep And Its Seasonal Variations in Three Pre-Industrial Societies, Current Biology, November 2015
Researchers studied members of 3 groups, 2 in Africa and 1 in South America, and found they slept 5.7 to 7.1 hours a night. Napping and insomnia were almost nonexistent. News sites are concluding:
Sleep Study On Modern-Day Hunter-Gatherers Dispels Notion That We’re Wired To Need 8 Hours A Day, Washington Post, 15 October 2015
Remember, this is a population study, an epidemiological study. It can inform our thinking; it allows us to draw hypotheses. It was not designed, nor can it tell us the answer to the question: What is the ideal length of time for humans to sleep? Even if it could, that time would vary by age, health, lifestyle, and other variables. You simply cannot claim that we need less than 8 hours of sleep, as the author of the Washington Post article did, given this data. That was a made-up story to sell their site, to sell advertising. That is what news stories have become.
First of all, look at the tables. There were 94 participants. Their average age was 30.4. For the 54 subjects from South America the average age was 24.9. There was no data collected on sleeping times (including naps and insomnia) in children, teenagers, or adults over 55.
Hadza, average age 36.6, 10 participants
Tsimane, average age 24.9, 54 participants
San, average age 38.2, 30 participants
These are people in the thick of their child-bearing years and in excellent health (“those who were ill were excluded” “caffeine or alcohol use excluded”). Because of their life-stage alone, they have a different physiology than children, teenagers, and older adults. Perhaps napping would have been found if they studied younger people, insomnia if they studied the elderly or women and men experiencing a mid-life change in hormones.
Their lifestyle is very different from ours, for example:
The Hadza sleep on animal skins on the ground. Families sleep close together, 2-6 people often sharing a single sleeping space. San participants slept on a blanket on the ground, covered by an additional blanket, without pillows in the winter and without a blanket or much clothing in the summer. Tsimane participants slept on beds above-ground made of tree-bark slats.
Each population eats locally acquired foods. The San eat meat from local game, baobab fruit, fish and berries. The Hadza eat game meat, baobab fruit, honey, tubers, and berries. The Tsimane eat a mix of hunted game, fish, and cultivated plant foods, primarily rice, manioc and plantains.
You just cannot extrapolate these data onto modern humans at all life stages, as news sites were prone to do. The National Sleep Foundation recommends a sleep duration of 7 to 9 hours for adults 18 to 65 years old. I don’t see how this one study of 94 pre-industrial-living, young adults would impact that advice.