The Myth of the Eight-hour Sleep

A

We often worry about lying awake in the middle of the night – but it could be good for you. Indications from both science and history suggest that the eight-hour sleep may not be a natural or inborn pattern for humans. In the early 1990s, psychiatrist Thomas Wehr conducted research which implies just that. Wehr kept a group of people in a darkened room for 14 hours a day for a month. It took some time for their sleep to regulate, but by the fourth week the subjects had settled into a very distinct sleeping pattern. Firstly, they slept four hours, then woke for one or two hours before falling into a second four-hour sleep. Though sleep scientists were impressed by the implications of the study, the idea that we must sleep for eight consecutive hours persists amongst the general public.

B

In 2001, historian Roger Ekirch of Virginia Tech University in the US published a paper drawn from 16 years of research, revealing historical evidence that humans used to sleep in two distinct periods of time each night. Ekirch's research found more than 500 references to a segmented sleeping pattern – in diaries, court recorders, medical books and literature, from the ancient Greeks to tribes in Nigeria. Much like Wehr's findings, these references describe a first sleep which began not long following sunset. Then there was a waking period of one or two hours and after that a second sleep. During the waking period, people could be quite active. They sometimes got up and moved around the house, although most people stayed in bed, and perhaps read or wrote if they had enough money for candles. In many historic accounts, Ekirch found that people used the time that they were awake between periods of sleep to think about and attempt to analyse their dreams.

In his book, Evening's Empire, historian Craig Koslofsky suggested an explanation for this divided sleep pattern in Europe. ‘Associations with night before the 17th century were not good,’ he writes. He goes on to explain that the streets of cities and towns at night were often populated by thieves or worse. The streets at night consequently scared many people. Even the wealthy, who could afford to light their way, had better things to spend their money on. There was no prestige or social value with going out or staying up late at night.

C

Ekirch found that references to the first and second sleep started to disappear during the late 17th century. The pattern began to alter first among the urban upper classes, changing amongst the rest of Western society later. By the 1920s, the idea of a first and second sleep had receded entirely from our social consciousness. Ekirch attributes the initial shift to improvements in street and home lighting. As the night became a time for all kinds of activity, the length of time people used for rest declined.

In 1667, Paris became the first city in the world to light its streets, using wax candles in glass lamps. It was followed by another French city, Lille, in the same year and by Amsterdam in Holland two years later, where a much more efficient oil-powered lamp was developed. London didn't light its streets until 1584, but by the end of the 17th century, more than 50 of Europe's major towns and cities were lit at night. Coffee houses emerged as a fashionable phenomenon and many were open virtually around the clock. Going out at night became commonplace, and spending hours lying in bed was considered a waste of time. ‘People were becoming increasingly time-conscious and sensitive to efficiency, certainly before the 19th century,’ says Ekirch. ‘But the Industrial Revolution intensified that attitude considerably.’ Strong evidence of this shifting attitude is contained in a medical journal from 1829 which urged parents to force their children out of the pattern of first and second sleep.

D

Today, most people seem to have adapted quite well to the eight-hour sleep, but Ekirch believes many sleeping problems may have roots in the human body's natural preference for divided sleep, as well as in difficulties caused by extended exposure to artificial light in the modern world. This could be the cause of a condition called sleep maintenance insomnia, where people wake during the night and have trouble getting back to sleep. The condition first appears in literature at the end of the 19th century, at the same time as accounts of interrupted sleep disappear.

E

Sleep psychologist Gregg Jacobs says that the idea that we must sleep for an extended period of time could be changing. It makes people who wake up in the night anxious, as this anxiety can itself discourage sleep and is likely to affect waking life too. Jacobs suggests that the waking period between sleeping, when people simply rested and relaxed, could have played an important part in the human capacity to regulate stress naturally. Russell Foster, a professor of circadian (body clock) neuroscience at Oxford University in the UK, shares this point of view. ‘Over 30% of the medical problems that doctors are faced with stem directly or indirectly from sleep. But sleep has been ignored in medical training, and there are very few countries where sleep is studied,’ Foster says. He feels this needs to change.