Studies Find Link Between Sleep, Weight Gain
People who sleep fewer hours are likely to have increased body mass indices, comparatively low levels of appetite-suppressing hormones and higher levels of appetite-stimulating hormones, according to recent studies published in the Public Library of Science and the Dec. 7 issue of the Annals of Internal Medicine, the Milwaukee Journal-Sentinel reports. Descriptions of the studies are provided below.
- Researchers from the University of Wisconsin-Madison and Stanford University studied data from 1,024 volunteers involved in the Wisconsin Sleep Cohort Study (Quick, Milwaukee Journal Sentinel, 12/13). The researchers examined sleep logs kept by participants and the duration of participants' sleep during nights spent at a sleep lab. They also analyzed blood samples taken from the subjects (Mestel, Los Angeles Times, 12/13). Researchers found that participants who slept fewer than eight hours per night had comparatively low levels of leptin, which is produced in fat cells and is known to influence appetite, and higher amounts of ghrelin, an appetite stimulant, in their blood stream. According to the study, people who regularly slept five hours per night showed a 14.9% increase in ghrelin and a 15.5% decrease in leptin compared to people who slept eight hours per night. According to the study, people who slept five hours each night had a 3.6% increase in BMI. The study results "boos[t] earlier findings" of a causal relationship between sleep and weight, according to the Journal Sentinel. Emmanuel Mignot, lead author of the study and a Stanford professor of psychiatry and behavioral sciences, said the study shows a person's BMI is directly related to hormone levels, and therefore, to sleep patterns. Mignot said that further studies must be done to validate the findings.
- A second study by researchers from the University of Chicago and published in the Annals of Internal Medicine involved 12 men and found similar results (Milwaukee Journal Sentinel, 12/12). For the study, participants were divided into two groups on two occasions. The first group was restricted to four hours of sleep, and the second group was told to sleep 10 hours. Each participant consumed the same amount of calories during the sleep regimens, and blood samples were taken regularly (Los Angeles Times, 12/13). The study found that participants who slept fewer hours had a preference for high-calorie, high-carbohydrate foods. Eve Van Cauter, lead author of the study and a professor of medicine at the University of Chicago, said that she did not know the reason for the specific food cravings but suggested that the brain "seeks simple carbohydrates when distressed by lack of sleep."
Daniel Kripke, a sleep researcher at the University of California-San Diego, said, "In general the effects reported [in the first study] were small." He added that the results "may be a societal association and not a biological" one.
Kripke also noted that the researchers studied a "rather obese population," and the results might not be "generalizable." He added, "[E]ven 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 noted that studies he has conducted have shown that people who sleep for more than eight hours also tend to weigh more.
However, Kripke and colleagues have reported similar associations between a lack of sleep and obesity, according to the Journal-Sentinel (Milwaukee Journal Sentinel, 12/12).
Shahrad Taheri, a lecturer at the University of Bristol in England and co-author of the first study said, "Sleep is not going to be the only answer, but we need to look into it" (Los Angeles Times, 12/13).
Mignot said, "I don't want people to overreact" to the findings. "I don't want someone saying, 'Oh, I need to lose 100 pounds, so I'll just sleep a lot,'" he said (Milwaukee Journal Sentinel, 12/12). An abstract of the second study is available online.