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People may not need all that eight hours of sleep after all, sleep scientists suggested this week.
The scientists cited a growing body of evidence from science and history that suggests eight hours of sleep may be unnatural, the BBC reported.
Historian Roger Ekirch of Virginia Tech published in 2001 a seminal paper based on 16 years of research, showing historical evidence that humans used to sleep in two distinct chunks.
Ekirch also cited a 1595 engraving by Jan Saenredam indicating evidence of activity at night.
These references describe a first sleep which began about two hours after dusk, followed by waking period of one or two hours and then a second sleep.
"It's not just the number of references - it is the way they refer to it, as if it was common knowledge," Ekirch said.
Experiment shows 4-2-4 pattern
In the early 1990s, psychiatrist Thomas Wehr conducted an experiment where a group of people were plunged into darkness for 14 hours every day for a month.
By the fourth week the subjects had settled into a distinct sleeping pattern - sleeping first for four hours, waking for one or two hours, then falling into a second four-hour sleep.
However, while sleep scientists were impressed by the study, the idea that people must sleep for eight consecutive hours has persisted.
During the waking period, people were active, often getting up, going to the toilet, smoking tobacco or even visiting neighbors.
Most people stayed in bed, read, wrote and often prayed.
Countless prayer manuals from the late 15th Century offered special prayers for the hours in between sleeps, the BBC report said.
"And these hours weren't entirely solitary - people often chatted to bed-fellows or had sex," it said.
It also cited a doctor's manual from 16th Century France that even advised couples that the best time to conceive was not at the end of a long day's work but "after the first sleep," when "they have more enjoyment" and "do it better."
First and Second Sleep
Ekirch also found references to the first and second sleep started to disappear during the late 17th Century.
This started among the urban upper classes in northern Europe and over the course of the next 200 years filtered down to the rest of Western society.
By the 1920s the idea of a first and second sleep had receded entirely from our social consciousness.
Ekirch attributed the initial shift to improvements in street lighting, domestic lighting and a surge in coffee houses, which were sometimes open all night.
As the night became a place for legitimate activity and as that activity increased, the length of time people could dedicate to rest dwindled.
In his new book "Evening's Empire," historian Craig Koslofsky puts forward an account of how this happened.
"Associations with night before the 17th Century were not good," he says. The night was a place populated by people of disrepute - criminals, prostitutes and drunks. Even the wealthy, who could afford candlelight, had better things to spend their money on. There was no prestige or social value associated with staying up all night," he said.
But in the wake of the Reformation and the counter-Reformation. Protestants and Catholics became accustomed to holding secret services at night, during periods of persecution.
If earlier the night had belonged to reprobates, now respectable people became accustomed to exploiting the hours of darkness.
This trend migrated to the social sphere but only for those who could afford to live by candlelight.
With the advent of street lighting, socializing at night began to filter down through the classes.
In 1667, Paris became the first city in the world to light its streets, using wax candles in glass lamps. It was followed by Lille in the same year and Amsterdam two years later, where a much more efficient oil-powered lamp was developed.
London did not join their ranks until 1684 but by the end of the century, more than 50 of Europe's major towns and cities were lit at night.
Night became fashionable and spending hours lying in bed was considered a waste of time.
Roots of sleeping problems
While most people seem to have adapted to the eight-hour sleep, Ekirch believes many sleeping problems may be due to the human body's natural preference for segmented sleep as well as the ubiquity of artificial light.
This could be the root of a condition called sleep maintenance insomnia, where people wake during the night and have trouble getting back to sleep, he suggests.
The condition first appeared in literature at the end of the 19th Century, at the same time as accounts of segmented sleep disappear.
"For most of evolution we slept a certain way. Waking up during the night is part of normal human physiology," said sleep psychologist Gregg Jacobs.
Consolidated sleep: unhealthy?
Jacobs said the idea that people must sleep in a consolidated block could be damaging, if it makes people who wake up at night anxious, as this anxiety can itself prohibit sleeps and is likely to seep into waking life too.
Every 60 to 100 minutes, people go through a cycle of four stages of sleep.
Stage 1 is a drowsy, relaxed state between being awake and sleeping. Breathing slows, muscles relax, and heart rate drops.
Stage 2 is slightly deeper sleep, where one may feel awake. On many nights, one may be asleep and not know it.
Stages 3 and 4, or Deep Sleep, is a stage very hard to wake up from as this is when there is the lowest amount of activity in the body.
After Deep Sleep, people go back to Stage 2 for a few minutes, and then enter Dream Sleep - also called REM (rapid eye movement) sleep.
In a full sleep cycle, a person goes through all the stages of sleep from one to four, then back down through stages three and two, before entering dream sleep
"Many people wake up at night and panic. I tell them that what they are experiencing is a throwback to the bi-modal sleep pattern," said Russell Foster, a professor of circadian neuroscience at Oxford.
Still, most doctors still fail to acknowledge that a consolidated eight-hour sleep may be unnatural, the BBC report said.
"Over 30 percent 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 centres where sleep is studied," Jacob said.
Jacobs suggested that the waking period between sleeps, when people were forced into periods of rest and relaxation, could have played an important part in the human capacity to regulate stress naturally.
In many historic accounts, Ekirch found that people used the time to meditate on their dreams.
"Today we spend less time doing those things. It's not a coincidence that, in modern life, the number of people who report anxiety, stress, depression, alcoholism and drug abuse has gone up," said Jacobs. — TJD, GMA News