Sleep time in hunter-gatherer groups on low end of scale
People in preindustrial societies may have less insomnia but no more shut-eye, study finds
People in the postindustrial world don’t always get a sound night sleep. But they appear to spend a similar amount of time sleeping as do people in hunter-gatherer communities in Africa and South America, a new study finds.
“It’s absolutely clear that they don’t sleep more than we do,” says Jerome Siegel, a UCLA sleep scientist.
In fact, on average, hunter-gatherers may sleep a little less.
Recommended nightly sleep for adults is typically seven to nine hours; a 2013 Gallup poll showed that most Americans get around 6.8 hours. On most nights, members of three hunter-gatherer groups — the Hadza of Tanzania, the Ju/’hoansi San of Namibia and the Tsimane of Bolivia — sleep 5.7 to 7.1 hours, Siegel and colleagues report online October 15 in Current Biology. That’s on the lower end of the sleep spectrum in postindustrial societies, the researchers say.
Evidence from the new study also suggests that these groups experience less insomnia than sleepers in postindustrial societies. (The three hunter-gatherer languages even lack a word for insomnia.)
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Hunter-gatherer sleep patterns are closely tied to temperature, a new study shows. Among the Hadza of Tanzania, for instance, people fell asleep about three hours after sunset, on average, as ambient temperatures decreased. People then woke up about an hour before sunrise, when temperatures reached their lowest point.
Source: G. Yetish et al/Current Biology 2015
These groups are isolated, without the shine of streetlights or the glow of computer screens that many people blame for sleeping problems. But Siegel and other sleep researchers say that faulting modern technology might be misguided. That’s because most sleep studies take place under controlled environments in the laboratory and often fail to involve more than one group or population.
“We’ve been studying sleep in one small slice of humanity living under particular postindustrial conditions and making assumptions,” says Carol Worthman, an anthropologist at Emory University.
“Just on the descriptive level, we are incredibly interested in seeing this [study] because there’s a complete lack of data,” she says.
For instance, temperature is a variable often underrepresented in sleep research. But in this study, sleep habits of each hunter-gatherer group was closely tied with temperature. The hunter-gatherers typically fell asleep several hours after sunset with falling ambient temperature, and awoke before dawn when the temperature reached its lowest point of the day.
“Presumably, part of our sleep machinery is reacting to temperature,” Siegel says.
He’s not suggesting that people will sleep better if they follow temperature schemes similar to those the hunter-gatherer communities experience. But it’s possible, Siegel says, that sleep researchers could benefit from learning about sleep in more natural environments. Since these hunter-gatherers live in a similar environment as humans’ ancestors, he says, sleep in these societies may be more representative of sleep in the past.
Worthman says that studies like this one could help people to lead healthier lifestyles.
“This is exciting because it doesn’t say we’re going to completely change what we think about sleep science or as a society, but it does raise new questions,” Worthman says. “It’s about how can we not just live smart but sleep smart.”