Headline Nov 05, 2015/ ''' SLEEPING STUDENTS -by- H E C T I C DREAMS '''

''' SLEEPING STUDENTS -by- 

H E C T I C DREAMS '''

BUT Dr. Siegel said he worried that putting a number on the amount of sleep people require could could push those who get less to resort to sleeping pills, which carry severe side effects.

Jim Horne, the director of the  Sleep Research Center at Loughborough University in England, called the new study ''excellent and very timely,'' and he said it suggests that sleep quality was much more important than quantity.

Many researchers argue that the invention of the electric light bulb in the late 1800s dramatically changed our sleep patterns.

Exposure to artificial light at night, whether from light bulbs or computer screens, throws off the body's biological clock, delaying and reducing sleep, these experts believe.

Some historians have also argued it is not natural for people to sleep straight through the night. They say that before the introduction of artificial light it was normal for people to sleep in two intervals separated by an hour of wakefulness, a phenomenon known as segmented sleep, or  ''first'' and ''second'' sleep.

But Dr. Siegel said he always questioned those assertions because there were no rigorous studies of sleep behaviour back then. He and his colleagues decided that one way to get some insight was to study cultures relatively unaffected by artificial light.

Among they chose to follow were the Hadza people, who spend their days hunting and foraging in northern Tanzania, much as their ancestors have for tens of thousands of years; the San of Nimibia, who have lived as hunter gatherers in the Kalahari for at least 20,000 years.

And the Tsimane, a seminomadic group that lives in the Andean foothills of Bolivia, near the farthest reaches of the human migration out of Africa. Members of the various tribes were fitted with small wrist-watchlike devices that tracked their sleep patterns and their exposure to light across the seasons.

The researchers found that in addition to sleeping roughly similar amounts each night, the three groups rarely took naps during the day and did not sleep in two separate intervals at night.

But Siegel said : ''The Hadza and the San live in the area where we humans evolved, and then the Tsimane live in some sense at the end of human migration. The fact that we see very similar sleep times gives me great confidence that this is how all our ancestors slept.

Their sleep did not seem to be problematic. Chronic insomnia, which affects 20 percent to 30% of Americans, for example, occurred in just 2% of the hunter-gatherers. The San and the Tsimane did not even have a word for it.

The groups did not go to sleep at sunset and they did not wake up at sunrise, suggesting that light exposure did not have much influence on their sleep patterns. 

But they almost always fell asleep as temperatures began to fall at night, and they would wake up right as the temperatures were rising again.

That suggests that human may have evolved to sleep during the coldest hours of the day, perhaps as way of to conserve energy, Dr.Siegel said.

''Today we  sleep in environments with fixed temperatures, but none of our ancestors did,'' he said. 

''We evolved to sleep in a natural environment where the temperature falls at night. Whether we can treat insomnia by putting people in an environment where the temperature is modulated in this way is something to be studied in the future.'' 

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