Stay up late and crawl out of bed too early and you'll get what's coming to you: baggy eyes, a foul mood and _ just maybe _ some extra body fat thrown in for good measure.
Chronic lack of sleep could be one reason people in the United States are getting so broad in the beam, suggest the authors of two studies. Their research found that going without sleep seems to elevate blood levels of a key appetite-stimulating hormone, ghrelin. It causes levels of a "stop eating!" hormone, known as leptin, to take a dive. The likely net effect is an increase in appetite.
"Sleep is not going to be the only answer, but we need to look into it," said Dr. Shahrad Taheri, a lecturer in medicine at the University of Bristol in England, lead author of one of the studies, published in the journal Public Library of Science Medicine.
In work conducted at Stanford University and the University of Wisconsin, the scientists examined data from 1,024 volunteers in a long-term sleep study conducted at the Madison, Wis., campus. They examined the sleep logs kept by the subjects as well as the duration of their sleep during nights spent at a sleep lab. Analyzing blood samples taken from the subjects, the researchers found a clear pattern. Those who slept the least had the most ghrelin and the least leptin, and for those who slept the longest, vice versa.
The scientists also found that the subjects with the least sleep had a larger body mass index, a widely accepted measure of whether someone's overweight.
The other study, published in the Annals of Internal Medicine and conducted at the University of Chicago, artificially altered the sleep patterns of 12 healthy men. Each was given two days of restricted sleep (just four hours in bed) or extended sleep (10 hours in bed) on two occasions. All men consumed the same amount of calories during the sleep regimens, and blood samples were regularly drawn.
Again, the scientists found increases in ghrelin and decreases in leptin associated with sleep deprivation. They also found that the volunteers rated themselves as significantly hungrier _ especially for high-calorie foods _ when they had been deprived of sleep.
It does make sense that the body would seek more nourishment if a person is up and about instead of sleeping, said Eve Van Cauter, senior author of the Annals paper.
The findings, though intriguing, don't prove that getting extra sleep will help shed fat, said Joel Elmquist, an associate professor at Harvard Medical School.
"But a good night's sleep _ that's not a bad thing to recommend."