People who sleep fewer than six hours a night -- or more than nine -- are more likely to be obese, finds a new government study, 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 shut-eye, said 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 is based on door-to-door surveys of 87,000 U.S. adults 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 it's not clear, for example, whether smoking causes sleeplessness or sleeplessness prompts smoking, said Charlotte Schoenborn, the study's lead author.

The study 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 less than six hours of sleep; 31 percent said they were current smokers. Those who slept nine hours or more were also big puffers: 26 percent smoked. For those who slept seven to eight hours, the rate was 18 percent.

About 33 percent of those who slept less than six hours were obese, as were 26 percent for those who slept nine hours or more. Normal sleepers were the thinnest group, with obesity at 22 percent.

Those who slept the least were the biggest drinkers.

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 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.

-- Mike Stobbe, Associated Press