People who sleep fewer than six hours a night — or more than nine — are more likely to be obese, according to a new government study that is one of the largest to show a link between irregular sleep and big bellies.

The study also linked light sleepers to higher smoking rates, less physical activity and more alcohol use.

The research adds weight to a stream of studies that have found obesity and other health problems in those who don't get proper shuteye, said Dr. Ron Kramer, a Colorado physician and a spokesman for the American Academy of Sleep Medicine.

"The data is all coming together that short sleepers and long sleepers don't do so well," Kramer said.

The study released Wednesday is based on door-to-door surveys of 87,000 U.S. adults from 2004 through 2006 conducted by the National Center for Health Statistics, part of the Centers for Disease Control and Prevention.

Such surveys can't prove cause-effect relationships, so — for example — it's not clear if smoking causes sleeplessness or if sleeplessness prompts smoking, said Charlotte Schoenborn, the study's lead author.

It also did not account for the influence of other factors, such as depression, which can contribute to heavy eating, smoking, sleeplessness and other problems.

Smoking was highest for people who got under six hours of sleep, with 31 percent saying they were current smokers. Those who got nine or more hours also were big puffers, with 26 percent smoking.

The overall U.S. smoking rate is about 21 percent. For those in the study who sleep seven to eight hours, the rate was lower, at 18 percent.

Results were similar, though a bit less dramatic, for obesity: About 33 percent of those who slept less than six hours were obese, and 26 percent for those who got nine or more. Normal sleepers were the thinnest group, with obesity at 22 percent.

For alcohol use, those who slept the least were the biggest drinkers. However, alcohol use for those who slept seven to eight hours and those who slept nine hours or more was similar.

In another measure, nearly half of those who slept nine hours or more each night were physically inactive in their leisure time, which was worse even than the lightest sleepers and the proper sleepers. Many of those who sleep nine hours or more may have serious health problems that make exercise difficult.

Many elderly people are in the group who get the least sleep, which would help explain why physical activity rates are low. Those skimpy sleepers who are younger may still feel too tired to exercise, experts said.

Stress or psychological problems may explain what's going on with some of the lighter sleepers, experts said.

Other studies have found inadequate sleep is tied to appetite-influencing hormone imbalances and a higher incidence of diabetes and high blood pressure, noted James Gangwisch, a respected Columbia University sleep researcher.

"We're getting to the point that they may start recommending getting enough sleep as a standard approach to weight loss and the prevention of obesity," said Gangwisch, who was not involved in the study.

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