We’ve been told by health experts, and it’s conventional wisdom, that we should sleep between seven and eight continuous hours a day as an adult. Yet, the assumption that an eight-hour block of sleep is the ideal or norm may be a myth.

Numerous studies have been published concerning the dangers of lack of sleep, to our brain and general health and longevity. In just one recent example, scientists have found that sleep allows our brains to clean themselves of toxins.

Yet, the insistence that "monophasic" sleep, with eight hours of continuous nightly rest, is the necessary way to refresh ourselves not only creates stress for people who are unable to achieve that goal, but ignores other common variations in sleep patterns, and historical precedent as well.

“Everyone is different," says Matt Bianchi, director of the sleep division at Massachusetts General Hospital. "Some people drink caffeine and get a rush while others don’t. One person might be fitted for polyphasic sleep [sleeping in short multiple blocks throughout the day], but someone else gets sleepy and crashes their car.”

We're familiar with the stories of polyphasic sleepers such as Leonardo da Vinci, Thomas Edison, Nikola Tesla, Buckminster Fuller and Margaret Thatcher, who got along fine with as little as four hours sleep each night, but little attention is paid to such sleep cycles today.

Consider these underexplored variations on daily sleep:

* The Biphasic Schedule: Two three-to-four-hour sleeps with an hour of awake time in the middle.

* The Dymaxion Sleep Schedule: 30-minute “naps” every 6 hours.

* The Uberman Schedule: Six 30-minute naps per day.

* The Everyman Schedule: A daily three-hour sleep plus three 20-minute naps.

All of these alternative sleep schedules are linked to evolution and history. A 2007 report from the Journal of Sleep, for example, found that the majority of animals on earth sleep on polyphasic schedules.

Most people in advanced countries today follow monophasic sleep cycles, or try to, but advocates of polyphasic sleep argue that their approaches trick the body into entering REM sleep more quickly, making the total length of sleep time less of an issue. Critics of monophasic sleep also argue that eight-hour sleep schedules just don’t account for individual differences. For example, it's believed that as much as three percent of the population can survive on only a few hours of sleep per night without ill effects.

History yields valuable insights regarding sleep. According to some recent research, until the age of electricity many people slept in two segments. They would wake up in the night for an hour or two, then return to sleep for another block of time. “The dominant pattern of sleep, arguably since time immemorial, was biphasic,” says Roger Ekirch, a sleep historian at Virginia Tech University and author of At Day’s Close: Night in Times Past. "Humans slept in two four-hour blocks, which were separated by a period of wakefulness in the middle of the night lasting an hour or more. During this time, some might stay in bed, pray, think about their dreams or talk with their spouses. Others might get up and do tasks or even visit neighbors before going back to sleep.”

References to “first sleep” or “deep sleep,” and “second sleep” or “morning sleep” abound in historical legal depositions, works of literature, and other pre-Industrial era archival documents. Gradually, during the 19th century, references to segmented sleep disappeared, Ekirch says, "and now people call it insomnia.”

Electric light at night now disrupts our circadian clock. The body reacts to bright light the same way it does to sunshine; too much can stop it from releasing melatonin, a hormone that regulates sleep.

In the 1990s, sleep scientist Thomas Wehr discovered that most people will sleep biphasically when subjected to natural patterns of light and dark, supporting Ekirch’s findings.

Yet this research struggles to gain a wider audience. In an article in Psychiatric Times, Brown Medical School psychiatrist Walter Brown writes: “The general public seems to regard seven-to-eight hours of unbroken sleep as a birthright; anything less means that something is awry. Sleep specialists share this assumption.”

In other words, if you wake up in the middle of the night, don’t worry about it. “Waking up after a couple of hours may not be insomnia,” Wehr says. “It may be normal sleep.”

Ekirch adds, “If people don’t fight it, they’ll find themselves falling asleep again after one hour.”

Instead, many people who wake up in the middle of the night today automatically become anxious about not sleeping or reach for sleeping pills.

Our modern society, with its many stimuli, and an environment full of light, has partially created this hysteria about sleep, and combined with the myth that an 8-hour block of continuous sleep is essential, does all of us a disservice. Don’t forget about the well-documented benefits of incorporating naps into your day.

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