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Dec. 13, 2004 Research finds link between obesity, sleep shortage By Susanne Quick MILWAUKEE - (KRT) - It's not sheep the sleep-deprived are counting, but jelly doughnuts and Cheetos. New research from the University of Wisconsin-Madison, Stanford University and the University of Chicago are boosting earlier findings of a relationship between sleep and weight: The less sleep a person gets, the more weight is gained. And the culprits appear to be two hormones: leptin, an appetite suppressor, and ghrelin, and appetite stimulator. One study appears in the Public Library of Science and the other in the Annals of Internal Medicine. "This is the first study to look at the altered physiology" caused by sleeplessness in real life, said Terry Young, a professor in UW's department of population health sciences, and an author of the Public Library of Science paper. Using data collected from the Wisconsin Sleep Cohort Study, a population-based longitudinal study of 1,024 volunteers, the researchers of the Public Library of Science paper showed that participants who slept fewer than eight hours not only had increased body mass indexes, or BMIs, but they also had comparatively low levels of leptin and high amounts of ghrelin in their blood stream. The data suggest that BMI is causally related to these hormone levels, and therefore to sleep patterns, said Emmanuel Mignot, lead author of the study and a professor of psychiatry and behavioral sciences at Stanford. But he stressed that intervention studies need to be undertaken in order to prove causality. Others cautioned that the findings were too insignificant. Leptin, which is produced in fat cells, is known to influence appetite: The less leptin produced, the hungrier the person. "So, mice who do not produce leptin are really, really fat," because they have insatiable appetites, said Mignot. And ghrelin - leptin's counterpart - works in the opposite way. The more ghrelin a person has, the more they want to eat. According to the study, people who regularly slept five hours a night showed a 14.9 percent increase in ghrelin and a 15.5 percent decrease in leptin when compared with people who slept eight hours a night. They also had a 3.6 percent increase in BMI. What's probably happening, said Mignot, is that people who are getting too little sleep are being hormonally stimulated to eat more. The result - they raid the refrigerator and gain weight. The University of Chicago study, which appears in the Annals of Internal Medicine, showed similar results, although the study group focused on just 12 men. "Their study really complemented ours," said Mignot. And it added another piece of information. Not only did the Chicago researchers note hormonal changes, but they also observed a preference for calorie-dense, high-carbohydrate foods in people getting too little sleep. "We don't know why food choice would shift," said Eve Van Cauter, a professor of medicine at the University of Chicago and lead author of the second study. But she surmised that because the brain is fueled by sugars, "we simply suspect it seeks simple carbohydrates when distressed by lack of sleep." Daniel Kripke, a sleep researcher at the University of California, San Diego, said that although he found the Public Library paper interesting, he thought the findings were exaggerated. He did not comment on the Chicago study. "In general the effects reported were small," he said. Despite the fact that he and his colleagues had reported similar associations between a lack of sleep and obesity, "this may be a societal association and not a biological" one. One limitation of this paper, he said, is the researchers used a "rather obese population." Therefore, the results may not be "generalizable." Indeed, he pointed to a Japanese study, published earlier this year in the journal Sleep, which did not find an association between reduced sleep and obesity. The participants in that study were not as obese. In any case, he said, "even if there is a real association of sleep hours and these hormones, that does not prove that the relationships are causal. A large variety of influences could affect both sleep length and these hormones." He also pointed to findings that both he and the Public Library of Science paper showed: that more than eight hours is also correlated with weight gain. Mignot acknowledged that it was too early to prove causality. And in any case, he said, "I don't want people to overreact" to these findings. I don't want someone saying, `Oh, I need to lose 100 pounds, so, I'll just sleep a lot.'" Indeed, it's a bit more complicated than that, he said. But, it shouldn't come as a surprise that a lack of sleep may have an effect on health. "All you need to do is look in the mirror" after only getting a couple hours of sleep, he said, "to tell you that too little sleep is not good for you." |