Feb. 14, 2002 -- Wake up! It won't kill you, but staying in bed just might.
A six-year study of more than a million Americans shows that a good night's sleep lasts seven hours. More sleep isn't better. People who sleep for eight hours or more tend to die a bit sooner. Six hours' sleep, on the other hand, isn't that bad.
Study leader Daniel F. Kripke, MD, tells WebMD that this is good news for most of us. The average American gets six-and-a-half hours of sleep on a weeknight.
"You really don't have to sleep for eight hours and you don't have to worry about it," says Kripke, a professor of psychiatry at the University of California, San Diego. "It is evidently very safe to sleep only seven, six, or even five hours a night."
The findings confirm earlier studies, says sleep expert Donald L. Bliwise, PhD, director of the program in sleep, aging, and chronobiology at Atlanta's Emory University. However, Bliwise warns that they don't mean it's good to get way too little sleep for too long.
"Getting a couple of nights' short sleep is nothing to be concerned about," Bliwise tells WebMD. "If someone on a chronic basis is truly getting a short amount of sleep -- less than five hours, night after night -- there are some concerns. If you are a long-haul truck driver getting by on four hours of sleep, week after week, that is just not good."
Kripke and co-workers analyzed data from an American Cancer Society study conducted between 1982 and 1988. The study gathered information on people's sleep habits and health, and then followed them for six years. Study participants ranged in age from 30 to 102 years, with an average starting age of 57 years for women and 58 years for men.
Because the study included 1.1 million people, the study could detect relatively small risks. For too much sleep, the risk of death over six years went up 12% for people who slept eight hours, 17% for those who slept nine hours, and 34% for those who slept 10 hours.
"For 10-hour sleepers, the increased risk of death was about the same as that for moderate obesity," Kripke noted.
Death risk increased for those who go too little sleep, too, but the numbers are smaller. The risk of death went up 8% for those who slept six hours, 11% for those who slept five hours, and 17% for those who slept only four hours a night.
While this increased risk is statistically significant, it doesn't translate into much of a risk for an individual person. The study's main finding, Kripke says, is that sleeping less than eight hours isn't bad for you. In fact, eight hours' sleep can no longer be considered normal.
So why does it feel good to sleep in? Oversleeping may be a lot like overeating, suggests Jim Horne, PhD, director of the sleep research center at Loughborough University, England.
"As we can eat more food than we require and drink more fluids than we require, or drink beer, or eat foods we don't need, we may sleep more than we require," Horne tells WebMD. "There is an optionality about it. The amount of sleep we require is what we need not to be sleepy in the daytime."
The Kripke study also shows that people who say they have insomnia aren't necessarily in bad health. But those who often take sleeping pills have an increased risk of death. Frequent use of sleeping pills increased the risk of death by 25%.
"The risk of taking a sleeping pill every night is equivalent to sleeping three or 10 hours," Kripke says. "It is a substantial risk factor. We cannot say it causes these deaths or that this risk applies to newer medicines. But lacking evidence for safety, the wisest choice is to be cautious in their use."
Bliwise says it's always a good idea to be cautious about using sleeping pills. However, he sees no real problem in the proper use of these drugs from time to time. "There is no data that intermittent use of a short acting [prescription sleeping pill] is necessarily harmful," he says.