Obesity linked to hormonal changes, lack of sleep
BY MICHELLE BRANDT
The less you sleep, the more weight you may gain.
So say School of Medicine researchers, who found in a recent study that sleep loss leads to higher levels of a hormone that triggers appetite, lower levels of a hormone that tells the body it’s full and an increased body mass index.
The findings not only add to the growing body of evidence showing that sleep duration may be an important regulator of body weight and metabolism, but they also document for the first time the relationship between sleep and these hormones in the general population, tracking how hormonal changes are consistent with obesity.
The paper by Emmanuel Mignot, MD, PhD, associate professor of psychiatry and behavioral sciences, and colleagues at Stanford and the University of Wisconsin was published Monday in the online issue of Public Library of Science.
“Our results demonstrate an important relationship between sleep and metabolic hormones,” the researchers noted in the paper. “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 findings have drawn much media attention, with Mignot being interviewed Tuesday on NPR’s Morning Edition, and USA Today, the San Jose Mercury News and other newspapers running stories on the work.
Past studies have indicated an association between sleep loss and increased body mass index, or BMI. A study presented last month at a meeting of the North American Association for the Study of Obesity, for example, found that people who sleep two to four hours a night were 73 percent more likely to be obese than normal sleepers.
Mignot and other researchers believe that sleep loss impacts several hormones related to appetite and food intake, and two such hormones—ghrelin and leptin—are thought to play a role in the interaction between short sleep duration and high BMI.
Ghrelin, which was discovered five years ago and is primarily produced by the stomach, triggers appetite in humans: the more ghrelin you have, the more you want to eat.
Leptin, a hormone produced by fat cells, is a signal indicating insufficient metabolic reserve and the need for consuming more calories. Low leptin levels are a signal for starvation and increased appetite.
While the hormone/sleep connection has been shown under highly controlled laboratory circumstances in past studies, Mignot and his team aimed to explore the connection in a general population sample.
During the study, the researchers examined the sleep patterns of 1,024 volunteers from the Wisconsin Sleep Cohort Study, a population-based longitudinal study of sleep disorders that began in 1989.
Participants between the ages of 30 and 60 underwent nocturnal polysomnography (a test in which a number of physiologic variables are measured during sleep) and blood sampling once every four years. They also reported on their sleep habits every five years through questionnaires and six-day sleep diaries.
The researchers’ data showed a 14.9 percent increase in ghrelin and a 15.5 percent decrease in leptin in people who consistently slept for five hours compared with those who slept for eight. Mignot said the results were consistent regardless of participants’ gender, BMI or eating and exercise habits. “The effect must be very strong to appear in [this entire] population,” he said.
“It was quite amazing that a hormone can track a person’s self-reported amount of sleep so well,” he added. “To my knowledge, this is the first time that a peripheral marker in the blood is shown to correlate with habitual sleep amounts in a general, normally behaving population.”
The researchers also found that in people sleeping less than eight hours (74.4 percent of the sample), increased BMI was proportional to decreased sleep. They reported that a 3.6 percent increase in BMI corresponded to an average nightly sleep decrease from eight hours to five hours.
While it remains unconfirmed whether observed changes in ghrelin and leptin are sufficient to produce increases in body weight, Mignot said he believed they were likely to do so because all the effects were in the right direction and of the expected magnitude.
Mignot said more studies on the direct effect of sleep loss on food intake, energy expenditure and obesity are needed. Altering sleep duration may prove to be an important way to treat obesity. Mignot is working on setting up a trial to study this approach.
The National Institutes of Health funded Mignot’s work.
Co-authors on the paper are Shahrad Taheri, MD, PhD, who conducted the research while at Stanford and is now at the University of Bristol; research associate Ling Lin, PhD; and Diane Austin and Terry Young, PhD, with the University of Wisconsin.