ATLANTA - 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 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,' he said.

The study, released on Wednesday, is based on door-to-door surveys of 87,000 adults in the United States from 2004 through 2006.

It was conducted by the National Centre for Health Statistics, part of the Centres 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 per cent saying they were current smokers.

Those who got nine or more hours also were big puffers, with 26 per cent smoking.

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

Results were similar, though a bit less dramatic, for obesity: About 33 per cent of those who slept less than six hours were obese, and 26 per cent for those who got nine or more.

Normal sleepers were the thinnest group, with obesity at 22 per cent.

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.

This 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. -- AP