Sleep study's surprise finding: Snooze eight hours, you lose
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WASHINGTON — Contrary to popular belief, people who sleep six to seven hours a night live longer, and those who sleep eight hours or more die younger, according to the largest study ever conducted on the subject.
The controversial study, which tracked sleeping habits of 1.1 million Americans for six years, undermines advice of many sleep doctors who long have recommended that people sleep eight or nine hours each night.
"There's an old idea that people should sleep eight hours a night which has no more scientific basis than the gold at the end of the rainbow," said Daniel Kripke, a University of California, San Diego, professor of psychiatry who led the study, published in today's Archives of General Psychiatry. "That's an old wives tale."
The study was not designed to answer why sleeping longer may be deleterious or whether people could extend life by sleeping less. Kripke said it was possible people who slept longer tended to suffer from sleep apnea, in which impaired breathing stresses the heart and brain. He also speculated that the need for sleep was akin to food — less is better for most people.
The study quickly provoked cautions and criticism. Some sleep experts said the problem with America's sleep habits was deprivation, not over-sleeping.
"None of this says sleep kills people," said Daniel Buysse, a University of Pittsburgh psychiatrist and the immediate past president of the American Academy of Sleep Medicine. "You should sleep as much as you need to feel awake, alert and attentive the next day. ... I'm much more concerned about people short-changing themselves on sleep."
Sleeplessness produces a variety of health consequences not measured in the study, critics said.
"The amount of sleep you get impacts how alert you are, your risk for accidents, how you perform at work and school," said James Walsh, president of the National Sleep Foundation, a nonprofit that advocates better sleep habits. "There's much more to life than how long you live."
The study used data from a survey conducted by the American Cancer Society between 1982 and '88. Women sleeping eight, nine and 10 hours a night had 13 percent, 23 percent and 41 percent higher risk of dying, respectively, than those who slept seven hours. Men sleeping eight, nine and 10 hours a night had 12 percent, 17 percent and 34 percent greater risk of dying in the study period.
Sleeping five hours a night increased the risk by 5 percent for women and by 11 percent for men. Among people who slept only three hours, women had a 33 percent increase in death, and men had a 19 percent increase, compared with those who slept seven hours.
Kripke noted that relatively few people slept so little, one in 1,000 people, whereas almost half of all people slept eight hours or more.
Participants were ages 30 to 102. Few reported frequent insomnia — which, despite popular belief, was not associated with an increased risk of death.
The study found that taking a sleeping pill every day increased the risk of death by 25 percent. "It appears there is no mortality risk to having insomnia," said Kripke, recommending that people not take pills routinely to ensure eight hours of sleep.
Acknowledging that the sleeping pills used between 1982 and '88 are not the same pills used today, he said, "without data showing that contemporary pills are safe, these data provide the best information about ... long-term use."
Kripke, whose study was funded by federal tax dollars, said doctors' recommendations that everyone sleep eight hours a night may have been influenced partly by drug companies that make sleeping pills. He cited a report from a public-relations firm representing the medicine Ambien, which gave the National Sleep Foundation money to alert people about an insomnia "public-health crisis" as part of a marketing campaign.
Critics Buysse and Walsh have served as paid consultants to sleeping-pill makers, but both denied being influenced by that. Walsh said most researchers in the field had accepted consulting fees from the companies, because "99 percent of the funding to support this type of research is from pharmaceutical companies."
Buysse, who wrote an editorial accompanying Kripke's article, said more research is needed to pin down the connection between sleep and risk of death. The study relied on people's reports of sleeping habits, which can be faulty. When asked how long they sleep, people usually report how long they spend in bed, he said.
That could mean people who reported sleeping eight hours really get about 7½ hours, putting them into the study's lower-risk category. Buysse also disagreed that sleep was like food, arguing that people can restrict sleep but cannot "choose" to sleep longer.
Other sleep experts noted that patients were not asked if they napped and that the study did not look at quality of sleep or whether participants felt drowsy all day.
Dr. Phyllis Zee, director of Northwestern Memorial Hospital's sleep-disorders center in Chicago, said the results probably do not reflect the general population because participants were not selected randomly but were mainly friends and relatives of volunteers for the American Cancer Society.
Zee said it is possible that participants who slept little or slept eight hours or more had medical problems that would explain their increased death rate.
Donald Bliwise, a psychologist at Atlanta's Emory University, said studies show that people allowed to sleep however long they want, without cues from clocks, often sleep 14 to 15 hours a day for the first few days. "Everyone walks around somewhat sleep-deprived," he said.
Information from The Associated Press is included in this report.