Experts challenge study linking sleep, life span

SAN DIEGO, California (CNN) -- Eight hours of nightly sleep is not the health panacea you were brought up to believe, according to a study released Thursday suggesting a link between too much slumber and a shorter life span.

Sleep experts immediately sought to debunk the conclusions as flawed and said they will only cause confusion.

The study, published in the Archives of General Psychiatry, included 1.1 million men and women and found the highest survival rate among those who sleep six to seven hours a night. The survival rate declines progressively among those who sleep eight hours or longer.

"Our study shows the average sleep for Americans of seven hours per night is safest," said Dr. Daniel Kripke, who led the study. Kripke is a professor of psychiatry who specializes in sleep research at the Univ. of California, San Diego. "You don't have to sleep eight hours per night; it's safe to sleep five, six or seven hours."

The study showed people who slept nine or 10 hours per night had a risk of dying similar to that associated with moderate obesity. Risk of death increased by 15 percent for those who slept eight hours a night, 20 percent for those who get 9 hours of sleep and 35 to 40 percent for those who sleep 10 hours a night.

"This is a happy message for five, six, seven hour sleepers and insomniacs that there's nothing to worry about. This is reassuring," said Kripke.

The National Sleep Foundation, which recommends eight hours of sleep per night for optimal health, immediately attacked the study's findings and said they can do nothing but cause the public unnecessary confusion and concern.

"The data can't be used to establish a cause and effect relationship because there are flaws in the study," said Dr. Russell Rosenberg, director of the Northside Hospital Sleep Medicine Institute in Atlanta.

"You can't tell how people rated their own sleep quality and looked back at their sleep, which is a subjective reaction to how much sleep they were getting."

The study included more than 1 million people who were friends or relatives of American Cancer Society volunteers and was designed to investigate causes of cancer. It included questions about sleep and sleeping pills.

The data was collected through questionnaires between 1982 and 1988.

"No one should change their sleep habits based on this study," said Rosenberg. "Many studies have shown insomnia leads to reduced test performance, school performance, increased risk of accidents and effects on the immune system. There is a wealth of information documenting those effects."

Kripke disagrees.

"I don't believe the body of science supports that argument," he said. "They have no data showing long sleep is safer."

The new study also showed a 25 percent increase in death risk for daily sleeping pill users, but Kripke said that has less meaning now because sleeping pills sold today are much safer than those used 20 years ago.

Kripke said people who now average 6 1/2 hours of sleep a night can be reassured they're getting a safe amount of sleep and from a health standpoint, there's no reason to sleep longer.

"There are a lot of reasons to get adequate sleep and mortality is only one outcome." said Rosenberg, "I would rather have five years of high quality life versus walking around like a zombie."