THURSDAY, March 27, 2003 (HealthDayNews) -- Getting along on six hours of sleep a night may not be something to brag about.
Researchers at the University of Pennsylvania have found that people who sleep for six hours or less a night for two weeks respond as poorly on standard cognitive tests as do people who don't sleep at all for three days. But they think they're doing fine, which is the problem.
"Contrary to the idea that people adapt to sleep deprivation, people develop a severe level of impairment when they have a sleep debt over a 14-day period, but they are not subjectively aware of their impairment," says Hans P.A. Van Dongen, an assistant professor of sleep and chronobiology at the University of Pennsylvania School of Medicine and author of a study tracking the effects of sleep debt.
This means, he says, that their reaction times, decision-making abilities and attention spans are compromised without them knowing it, which can mean trouble.
"Impairment is when mistakes happen, like car crashes, problems operating machinery, or more benign effects, like decision-making impairment," Van Dongen says.
The study results appear in the March 15 issue of Sleep.
"This excellent study adds to the literature on the cumulative effects of sleep restriction and is additional evidence that suggests that people cannot really get used to being sleep-deprived, which contradicts beliefs that are still held in the public," says Avi Sadeh, a psychology professor at the University of Tel Aviv. Sadeh is the author of another recent study that found similar cognitive impairments among children with slight sleep deprivation.
For this study, Van Dongen and his colleagues recruited 48 healthy men and women, aged 21 to 38, and divided them into four groups. Three of the groups slept for eight, six, and fours hours nightly, respectively, for two weeks. A fourth group slept for eight hours a night for two nights and then was kept awake for 88 hours without sleep.
During the study, the participants were tested every two hours for self-reports of sleepiness and were also given a series of five neurobehavioral tests to monitor their cognitive abilities, including their working memory, their attention span and their response times.
While those who slept eight hours nightly showed no slippage in their cognitive abilities, those who were sleep-deprived showed significant impairment in the tests.
An example, Van Dongen says, is in reaction times, which are measured in lapses, or reaction times longer than 500 milliseconds. This is the critical time for, say, seeing or missing a road signal. In those who got enough sleep, the respondents scored zero to one lapses over a 10-minute period in a reaction time test, but among those with less sleep, there were up to 16 lapses in the ten minutes.
Further, those with the four- or six-hour sleep times scored just as poorly on the cognitive tests as did those who had no sleep for three days, but those in the latter group were unaware they were impaired, Van Dongen says.
"What was worrisome was that as time went by during the study, the people who slept for four or six hours a night began to underestimate their performance impairment," Van Dongen says, compared to the group that stayed awake for 88 hours, who were very aware they weren't functioning at their best levels.
"These data are very consistent with other data. This study, however, does provide a very robust confirmation of the performance deficits associated with less than six hours sleep. This deficit can be very detrimental or even dangerous [e.g., driving] because part of the deficit is lack of appreciation of the increasing deficit," says Dr. Carl E. Hunt, director of the National Center on Sleep Disorders Research in Bethesda, Md.
For two weeks before the study, and during the study itself, participants abstained from caffeine, tobacco, alcohol or medications, all of which can be stimulants and mask the effects of sleep deprivation.
"People in the real world are using these things to stay awake, but when there's a critical situation, and the stimulants wear off, what you're left with is your intrinsic biology, and if that is impaired, that's when mistakes happen," Van Dongen says.
More information
Test your sleep IQ by taking a test from the National Center on Sleep Disorders. To help you get a good night's sleep, follow these tips from the National Sleep Foundation.
