The finding is based on data from the National Health and Nutrition Examination Survey I (NHANES I). More than 9,000 people participated in the initial study, which was conducted from 1982-1984. They were initially weighed, and later, researchers obtained a self-reported weight for follow-up. More than 8,000 people took part in a 1987 follow-up study.
People who reported getting less than seven hours of sleep a night were more likely to be obese on initial evaluation. The study also showed that they were also more likely to develop obesity during follow-up.
Participants who slept five hours per night were 73% more likely to become obese than those getting seven to nine nightly hours of sleep, say Columbia University professor of medicine Steven Heymsfield, and James Gangwisch, PhD.
Even one hour of sleep can make a difference.
People getting six hours of sleep per night were 27% more likely to become obese than those getting seven to nine hours.
The lightest sleepers -- those with only two to four hours of sleep per night -- were 67% more likely to become obese than people who slept for seven to nine hours.
Those numbers were calculated before taking other variables into consideration. However, the link between sleep and obesity held even after adjusting for those factors, say the researchers, who reported their findings in Las Vegas, at the annual scientific meeting of the North American Society for the Study of Obesity.
More work is needed to explain the sleep-obesity relationship, but the researchers have some ideas.
In a news release, Gangwisch says humans may have evolved to store fat in summer, which has short nights and plentiful food, to prepare for winter's long nights and historically scarcer food supply.
"As a result, sleeping less could serve as a trigger to the body to increase food intake and store fat," says Gangwisch.
Leptin is associated with appetite control and ghrelin has been identified as an appetite stimulant. During sleep deprivation, leptin levels fall and ghrelin levels rise.
That may be a recipe for ravenous, tired people who may end up raiding the refrigerator when they might be better off turning in earlier or hitting the snooze button.