Are You Sleeping Enough -- or Too Much?

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.