Whether and how these two trends are connected, however, is unclear. Sleep-deprived rats eat more than those allowed normal sleep. Several epidemiologic studies showed that people who sleep less are more likely to be overweight. One recent study found that those who reported less than four hours of sleep a night were 73 percent more likely to be obese.
By providing the first data on the relationship between sleep and the hormones that regulate hunger, this study helps to confirm and begins to explain the connection.
Van Cauter and colleagues studied 12 healthy male volunteers in their early 20s to see how sleep loss affected the hormones that control appetite. Theses hormones -- ghrelin and leptin, both discovered in the last ten years -- represent the 'yin-yang' of appetite regulation. Ghrelin, made by the stomach, connotes hunger. Leptin, produced by fat cells, connotes satiety, telling the brain when we have eaten enough.
Van Cauter's team measured circulating levels of leptin and ghrelin before the study, after two nights of only four hours in bed (average sleep time 3 hours and 53 minutes) and after two nights of ten hours in bed (sleep time 9 hours and 8 minutes). They used questionnaires to assess hunger and the desire for different food types.
"We were particularly interested in the ratio of the two hormones," said Van Cauter, "the balance between ghrelin and leptin."
After a night with four hours of sleep, the ration of ghrelin to leptin increased by 71 percent compared to a night with ten hours in bed.
As hunger increased, food choices changed. After two nights of curtailed sleep the volunteers found foods such as candy, cookies and cake far more appealing. Desire for fruit, vegetables or dairy products increased much less.
"We don't yet know why food choice would shift," Van Cauter said. "Since the brain is fueled by glucose, we
Contact: John Easton
University of Chicago Medical Center