Not getting enough shut-eye could be interfering with your ability to shed unwanted pounds. Previous research has shown that sleep could be a key regulator of body weight and metabolism. New findings link changes in two important appetite-regulating hormones to the amount of sleep people regularly get.

Shahrad Taheri, now at the University of Bristol, and colleagues analyzed data collected on 1,024 volunteers as part of the Wisconsin Sleep Cohort Study. Starting in 1989, the subjects filled out questionnaires and kept diaries that logged their sleep habits. In addition, once every four years they had their blood sampled and underwent tests that measured physiological variables while they slept. The researchers report today in the journal Public Library of Science: Medicine that people who consistently slept less than five fours a night had significant differences in the hormones leptin and ghrelin as compared with people who slept an average of eight hours a night. Leptin is produced by fat cells. Low levels of it are a signal of starvation and a need for a bigger appetite. Ghrelin, meanwhile, is produced by the stomach and is an appetite stimulant--the more ghrelin you have, the more you want to eat. The study subjects suffering a lack of sleep had 16 percent less leptin and nearly 15 percent more ghrelin than those who were well rested did. "In Western societies, where chronic sleep restriction is common and food is widely available, changes in appetite regulatory hormones with sleep curtailment may contribute to obesity," the team reports.

The results add to a growing body of evidence for a link between lack of sleep and increased weight and body mass index. "Good sleep, in combination with other lifestyle modifications, may be important in fighting obesity," Taheri says. Study co-author Emmanuel Mignot of Stanford University cautions that there is not yet enough evidence to establish a causal link, however. In the future, he hopes to investigate whether altering sleep patterns can help people fight the battle of the bulge. In such an intervention study, a group of overweight people could be told to change how much they sleep each night to study whether a few hours of extra shut-eye is associated with losing weight.

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