NEW YORK (Reuters Health) - A new study suggests that people who sleep 8 hours or more a night, or less than 4 hours, have a slightly higher risk of dying in a given time period than those who get 6 and 7 hours of shut-eye.

However, the researchers note that they can't be sure why some of the study subjects had longer or shorter sleep periods, and there's no evidence that sleep patterns-or changing them-can truly influence mortality risk.

Some sleep experts, including those at the National Sleep Foundation (NSF), agree.

"Although the study reports data that is of interest, limitations in the study methodology restrict the conclusions that can be reached, particularly about the amount of sleep needed to sustain an individual's health, safety and well being," according to a statement from the Foundation.

In the study, Dr. Daniel Kripke of the University of California in San Diego and colleagues examined the findings of a previously conducted study that included, among other things, data on the sleep habits of 1.1 million people men and women between the ages of 30 and 102. The study subjects, friends and family members of American Cancer Societyvolunteers, were interviewed in 1982 about diet, exercise, sleep and health problems and then followed up 6 years later.

Participants who reported sleeping 8 or more hours or less than 4 or 5 hours a night experienced a slightly higher chance of dying-at least a 15% increase in risk--within that time compared with those who slept 7 hours a night, the authors report in the February 15 issue of the Archives of General Psychiatry.

Furthermore, Kripke and his team report that insomnia was not associated with excess mortality, although the use of a prescription sleeping pill was also associated with a slightly increased risk of dying during the six-year period.

They note that the study could not prove that sleeping pills were responsible for the increased risk, and that the study subjects mostly took types of drugs that are no longer routinely given to people with insomnia. The study does seem to indicate that fewer than 8 hours of shut-eye a night are not necessarily detrimental to health, Kripke said.

"The average American sleeps 7 hours on weekdays, according to the 2001 Sleep in America Poll (conducted by the National Sleep Foundation)," he said in an interview with Reuters Health. "The new study shows that it is quite safe to sleep five, six, or seven hours a night, and people who sleep less than eight hours do not need to worry," said Kripke.

In an accompanying editorial Drs. Daniel J. Buysse and Mary Ganguli, of the Western Psychiatric Institute and Clinic in Pittsburgh, Pennsylvania, write that "while the data are intriguing one must resist the temptation to over-interpret them."

Buysse and Ganguli caution that the study's findings may lead the public to be less concerned about insomnia--a sometimes serious condition marked by an inability to sleep.

"Even mild sleep deprivation is associated with increased daytime sleepiness, which may lead to adverse outcomes, such as accidents," write Buysse and Ganguli.

Insomnia," they continue, " is associated with impaired quality of life, functional impairment, physical symptoms, [and] coronary heart disease."

"Sleep is not bad for you and insomnia is not good," conclude Buysse and Ganguli.

"I don't have a sense that this (study) represents the population at large," said Dr. Meir Kryger, a spokesperson for the National Sleep Foundation, in an interview with Reuters Health.

Kryger says that he hopes the public doesn't get the message that they should try and reduce the amount of time they sleep in an effort to reduce their risk of death.

"The findings are not compelling enough to warrant a change in behavior," he said.According to their statement, the National Sleep Foundation "emphasizes that substantial research serves as the basis for the recommendation that adults obtain an average of seven to nine hours of sleep each night."

The group notes that individuals will require different amounts of sleep and that if someone "sleeps 8.5 hours a night and feels alert and energetic, it would be incorrect to reduce sleep time based on the Kripke article."

"I myself need 8 hours sleep to avoid being sleepy," Kripke told Reuters Health, "So that is what I get."

"The increased risk of sleeping 8 hours is small, and we do not know if sleeping less would reduce the risk," he said.

SOURCE: Archives of General Psychiatry 2002;59:131-136.

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