Of course, these scientists didn't have time machines to peek in on our ancestors, so they did the next best thing to try to understand what "natural" sleep is: They studied the sleep patterns of three current preindustrial societies in Africa and Bolivia.
In other words, they found 94 people to observe who don't have the distractions of electric lighting, smartphones, Netflix and all the other trappings of modern life on which we blame our lack of sleep. The study ran in the latest edition of Current Biology.
What these scientists found was that despite their geographic and cultural differences, there was a pattern among all three groups: They were relatively healthy and they got only 6.4 hours of sleep on average a day (ranging from 5.7 to 7.1 hours per night), sleeping another hour more in the winter.
The Hadza, who live in northern Tanzania; the Tsimane, who live in Bolivia; and the San, who live in Namibia, helped these scientists dispel a few other notions people have about idyllic premodern sleeping. These peoples nearly never nap. They don't set a sleep schedule around when it's light out. Typically, they went to sleep three hours and 20 minutes after sunset and woke before sunrise. And they slept through the night.
The result of these sleep patterns: Nearly no one suffered from insomnia. In none of their languages is there even a word for insomnia. Most slept outside or in moderate huts.
By contrast, Americans -- even with all our modern conveniences such as adjustable beds, white-noise machines and zillion thread-count sheets -- say we really stink at sleeping.
An estimated 48% of Americans report
insomnia occasionally; 22% say they have insomnia every night or almost every night. An inability to sleep is not just annoying, it's dangerous and is tied to all sorts of health issues such as obesity, diabetes, depression and cardiovascular disease. It limits our mental and physical abilities overall.
In contrast, these peoples were generally healthy. They had fewer problems with high blood pressure and obesity and were physically fit. And before you say it is because of all the exercise they get hunting and gathering, previous studies have shown that their daily energy expenditure is similar to Americans'.
What's the difference?
It may be about sleep quality. Certainly, more research needs to be done, but Jerome Siegel,
one of the authors of the study, thinks what this research can do is take some of the pressure off people who feel like they are failing to get the prescribed amount of hours that public health agencies tell them they need.
The major sleep associations and the Centers for Disease Control and Prevention
suggest adults need between seven and eight hours
. But that could vary, depending on the person.
"I do think people are tired and that is a real problem," Siegel said. He is the past president of the Sleep Research Society and for 40 years has run a sleep research lab in Los Angeles. "I think that some people come in looking for help who are anxious, not because they are not rested but because they aren't hitting some prescribed number of hours or they think that we are all sleeping much less than our ancestors, and that is actually what is a fairly harmful idea."
Harmful, he say,s because when doctors hear this, they'll give patients a sleeping pill prescription when they may not need one. Pills, he said, may help you get to sleep faster, but they don't add to the length of your sleep.
Not that length matters as much as quality of sleep; it's better to feel rested rather than count the hours. And if you want to increase your likelihood of feeling rested, follow the usual sleep doctor suggestions: exercise, maintain a healthy weight, reduce your caffeine and alcohol intake, and wake up at a consistent time.
The other big takeaway from the study, Siegel said, was that it wasn't light that regulated a sleep pattern, it was the daily cycle of temperature change. With modern insulated buildings, that is a little difficult unless you leave a window open.
"Yes, turn off the lights, that is important for sleep, but also, you can find a way to moderate the temperature in your bedroom," Siegel said. "Under natural conditions, the temperature is not just lower at night, it is falling throughout this period."
More research will need to be done. This is a study among only 94 people, but Siegel said the results are intriguing: "These people are quite healthy, so there certainly are lessons here."