'Sleep Debts' Cause Poor Mental Functioning

Sleep: Don't be too sure you're getting enough of it.

Those who believe they can function well on six or fewer hours of sleep every night may be accumulating a "sleep debt" that undermines their mental performance during the day, according to researchers at the University of Pennsylvania School of Medicine.

But those people might be too sleep-deprived to know it, they said.

The study, published in Saturday's issue of the journal Sleep, found that chronically sleep-deprived volunteers reported feeling "only slightly sleepy" even when their performance was at its worst during standard psychological testing.

The results provide insight into the daily challenges that confront military personnel, residents and on-call doctors and surgeons, shift workers, parents of young children, and others who routinely get fewer than six hours of sleep each night, according to lead researcher David Dinges.

Researchers studied the effects of four hours of sleep vs. six hours of sleep per night on healthy volunteers ages 21 to 38 over a two-week period.

"Routine nightly sleep for fewer than six hours results in cognitive performance deficits, even if we feel we have adapted to it," said Hans Van Dongen, assistant professor of sleep and chronobiology in Penn's Department of Psychiatry.

"This work demonstrates the importance of sleep as a necessity for health and well-being," he said. "Even relatively moderate sleep restriction, if it is sustained night after night, can seriously impair our neurobiological functioning."