Stressed humans need more sleep, research finds

Humans who find themselves in stressful situations need to have had a full night's sleep to prevent memory loss, new Swedish research has found.

Scientists at Uppsala University found that only humans who lead stress-free lives can have full access to their memories on four hours of sleep, news agency TT reported on Saturday.

"The quality of sleep is the most important. Deep sleep plays an important role and it occurs the first hours after one falls asleep," Christian Benedict, one of the researchers behind the study, told TT.

The study had 15 people learn something before they went to sleep for either four or eight hours.

The two groups' recollection of the lesson only began to differ once the researchers had exposed them to "acute stress" after waking up, such as having to recall a newly learnt list of words while being exposed to loud noise.

Those who had slept four hours then saw their ability to memorize the previous night's lesson drop by 10 percent, the researchers found.

"We are always stressed. Someone might call you and ask you important things while you are in the store buying candy for your children," said Benedict, who reckons few ordinary humans can retain full recollection on less than seven hours of sleep.

"Students who are up studying all night to store as much as possible in their long-term memory have not found a good strategy, since they can't remember those things the following morning when they find themselves in the stressful situation of an exam," he said. Endit