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Reported by Norleena Gullett, M.D.:

Getting too little sleep is linked to a long list of health problems, including high blood pressure, diabetes and stroke. Now a new study suggests insufficient sleep can cause weight gain, too.

The small study followed seven healthy volunteers who underwent four nights of normal sleep - about 8.5 hours - followed one month later by four nights of sleep deprivation - when they were only allowed about 4.5 hours.

After four nights of restricted sleep, fat cells taken from the study participants' stomachs were less sensitive to insulin, a hormone that helps control blood sugar. And insulin insensitivity is linked to both obesity and diabetes.

"This is significant because sleeping four to five hours a night during the work week is not uncommon. People think they can function cognitively on little sleep, but our study proves they are not tolerating the metabolic consequences," said Dr. Matthew Brady of the University of Chicago, senior author of the study published Monday in Annals of Internal Medicine.

Previous studies have linked lack of sleep to weight gain, but this is the first to show how sleep deprivation affects fat cell function.

"Previously it was thought that if you were up at night, you were likely to eat more. You were also more likely to be tired the next day and not as physically active which could lead to weight gain," said Dr. Francine Kaufman of the University of Southern California's Center for Endocrinology, Diabetes & Metabolism.

The new study emphasizes "the importance of lifestyle changes for weight management, including physical activity, watching our diet, our weight, and now… sleep," Kaufman said.

"Most people need a good night of undisturbed sleep, ideally eight hours, but that's hard to get," said Dr. Gerald Bernstein, director of the Diabetes Education Program at Beth Israel Medical Center in New York. "People try to take naps, but it doesn't make up for a lack of sleep. It's not good sleep."

The study also raises questions about the effects of prolonged sleep deprivation. While good sleep practices like avoiding TV at night and using low lighting around the house can help one settle down for a night's sleep, many people struggle to get to bed on time because of work or childcare responsibilities.

How much sleep do you really need? "Ask yourself how many hours you sleep when you're on vacation," said Bernstein, adding that the ability to function on five hours of sleep is rare.

"Ninety-nine percent of people who think they only need five hours of sleep a night are actually hurting themselves," said Dr. Lee Green of the department of family medicine at the University of Alberta in Canada.