So you stayed up past your bedtime watching late-night TV, and that means you only got six hours of sleep. Many experts would say that spells trouble. But new research is challenging the notion that when it comes to sleep, more is always better.
In fact, people who reported sleeping more than eight hours a night have a 15 percent greater chance of dying, for any reason, than people who sleep seven hours a night. The same holds true for those who slept less than four or five hours, found researchers from the University of California, San Diego, and the American Cancer Society.
The use of sleeping pills was also associated with an increased mortality of 25 percent. And perhaps surprisingly, people who reported themselves to be insomniacs were not found to have any increased risk.
The study, which appears in the current issue of Archives of General Psychiatry, used data collected by the American Cancer Society in 1982 and 1988 that documents the sleep habits (including use of sleeping pills) of 1.1 million men and women ranging in age from 30 to 102.
"The main implication is good news," said Dr. Daniel Kripke, professor of psychiatry at UCSD and lead author of the study. "The average American sleeps six and a half hours [a night] and people who sleep five, six, or seven hours are perfectly safe and don't need to sleep any more."
Sleep Less, Live Longer?
Experts caution that the results of this study demonstrate only that there is a relationship between sleep and mortality and do not explain the underlying causes.
There may also be confounding factors that prevent these results from being extended to the general population.
"Although sizable, the study population [friends and relatives of American Cancer Society volunteers] is not a random sample and does not represent the entire population," said a representative of the National Sleep Foundation. "Geographic, racial and other factors of the study group are not indicated."
While the idea that sleeping less will lead to longer life cannot yet be proven, it has been examined in previous research.
"Most of the studies seem to support the idea that people who are very long sleepers and short sleepers may live less," said Dr. Phyllis Zee, director of the sleep center at Northwestern Memorial Hospital in Chicago. "But why? Is it a sleep-related issue, or is there an underlying problem for which sleep is a symptom?"
The bottom line is that it is still too early to say whether setting the alarm clock an hour earlier will help anyone break longevity records.
"If you have results [from studies] like these, it does not mean that people need less sleep," added Zee. "It could, but I don't think that it should be interpreted that way — at least not until more studies are performed."
Additionally, even if further research confirms that short or long sleepers have higher mortality rates, experts say they will still stress the importance of a good night's sleep, because living longer does not necessarily mean living better.
"There are many reasons to continue to urge people to obtain adequate sleep," says the National Sleep Foundation, which notes that bad moods, a higher risk for accidents and negative effects on the immune system are all associated with inadequate sleep. "Mortality is not the only important outcome measure."