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.