Last Updated: 2003-03-14 17:00:28 -0400 (Reuters Health)

By Dana Frisch

NEW YORK (Reuters Health) - Many nights of little sleep--fewer than six hours a night--can impair mental performance as much as not getting a wink for two nights in a row, new research shows.

The data contradict a popular notion that our bodies can become accustomed to functioning on sustained periods of little sleep without any consequences, said lead author Dr. Hans P.A. Van Dongen, a research assistant professor at the University of Pennsylvania School of Medicine in Philadelphia.

The 48 participants in the study were divided into four groups that slept either four, six or eight hours a night for two weeks, or had no sleep for three days. The groups were monitored in a laboratory throughout the two weeks to ensure that they did not nod off or use caffeine. They were assessed on a battery of mental and physiological tests periodically every day and were also asked to evaluate how tired they felt.

People sleeping less than eight hours a night were slower to react, less able to think clearly and perform simple memory tasks, the researchers report in the March issue of the journal Sleep. They also performed as poorly on certain tasks as the individuals evaluated after one or two nights of sleeplessness.

However, getting some sleep made individuals feel less tired than those who went without sleep despite test results that showed they were just as impaired.

As a consequence, Van Dongen told Reuters Health, there should be countermeasures in place for people who cannot avoid being chronically sleep-deprived, such as military personnel, trainee doctors, shift workers and others.

Van Dongen recommends that these professions limit the number of hours people are allowed to work, give people the opportunity to nap at "strategic times" or allow them to use caffeine or other chemical stimulants to maintain alertness.

This study is important and "relevant" because it shows what happens when the body alone must deal with its tiredness in the absence of chemical stimulants like caffeine or other distractions, said Dr. Meir Kryger, a professor of medicine at the University of Manitoba in Winnipeg, Canada, and a sleep researcher.

Data from the National Sleep Foundation show that Americans sleep an average seven hours a night during the week, although 31 percent of all adults regularly get less sleep.

The study also found that that there were large individual differences in how much people needed to sleep.

Kryger said in an interview that everybody needs a different amount of sleep. Getting sufficient amounts of shut-eye is a "life-style decision," he said. "It is one of the important functions of life and you need to control it."

SOURCE: Sleep 2003;26:117-126.


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