MIKE STOBBE

People who sleep fewer than six hours a night - or more than nine - are more likely to be obese, according to a new American 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 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," said Kramer.

The study published yesterday is based on door-to-door surveys of 87,000 US adults between 2004 and 2006 by the National Centre for Health Statistics, part of the Centres for Disease Control and Prevention.

However, such surveys cannot prove cause-effect relationships. For example, it is not clear if smoking causes sleeplessness or if 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, with 31% saying they were current smokers.

Those who got nine or more hours were also big smokers, around 26% of those surveyed. The overall US smoking rate is about 21%. For those in the study who sleep seven to eight hours, the rate was lower at 18%.

Results were similar, although less dramatic, for obesity.

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

For alcohol use, those who slept the least were the biggest drinkers.

However, alcohol consumption for those who slept seven to eight hours and those who slept nine hours or more was similar.

The study also found 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.

Stress or psychological problems may explain what is going on with some of the lighter sleepers.

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, who is a sleep researcher from Columbia University .

"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.