CHICAGO -- Don't fret if you don't get eight hours of sleep a night -- new research suggests adults live longer if they get six or seven.
Still, even the study's authors say it is not time to reset the alarm clock just yet.
The research is based on a nationwide survey of 1.1 million adults. It found that those who slept eight hours a night were 12 percent more likely to die within six years than those who got 6 1/2 to 7 1/2 hours of sleep. The increased risk was more than 15 percent for those who reported getting more than 8 1/2 hours or less than about 4 hours nightly.
The participants were ages 30 to 102. Few reported frequent insomnia -- which, despite popular belief, was not associated with an increased risk of death.
''Additional studies are needed to determine if setting your alarm clock earlier will actually improve your health,'' said lead author Dr. Daniel Kripke, a psychiatrist at the University of California at San Diego.
The study was published in February's Archives of General Psychiatry.
Sleep experts said the research, though provocative, has several flaws. The study was not actually designed to look at sleep's effect on longevity. It relied on patients' recollections of their sleep habits and did not ask if they took naps. It did not look at the quality of people's sleep or whether they felt drowsy all day.
Dr. Phyllis Zee, director of Northwestern Memorial Hospital's sleep disorders center, said the results probably do not reflect the general population because participants were not randomly selected but were mainly friends and relatives of volunteers for the American Cancer Society, which collected the data as part of a 1982 survey on cancer risks.
Zee said it is possible that participants who got little sleep or slept eight hours or more had medical problems that would explain their increased death rate.
About 5 percent of the women and 9 percent of the men died during the six years after the survey, with heart disease and cancer the leading causes.
The research neglects strong evidence that there are natural sleep variations, said psychologist Rosalind Cartwright of the sleep disorders center at Rush-Presbyterian-St. Luke's Medical Center in Chicago.
''There are natural-born short sleepers who are perfectly healthy with fewer than six or fewer hours,'' Cartwright said. ''They couldn't sleep more if you paid them -- because we've tried, and they can't.''
She added: ''There are natural-born long sleepers, who if they try to shorten their sleep to six hours, they're going to be grumpy.''
And even mild sleep deprivation may result in daytime sleepiness and accidents, as Drs. Daniel Buysse and Mary Ganguli of Pittsburgh's Western Psychiatric Institute and Clinic noted in an accompanying editorial.
On the Net: Archives: http://www.archgenpsychiatry.com
National Sleep Foundation: http://www.sleepfoundation.org
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