Researchers at the Mayo Clinic studied 12 healthy people in the hospital for a few weeks to control how much sleep they got and closely monitor how much they ate and the energy they exerted. The people in the study were not obese, and they ranged in age from 19 to 39.
The first 4 days, all of them were allowed to sleep for 9 hours. For the next 2 weeks, half of them were limited to 4 hours of sleep each night, while the rest could still sleep for 9 hours. After that, both groups had 3 days and nights of recovery, with 9 hours in bed. All the people involved could eat as much as they liked throughout the study.
The people who got less sleep ate, on average, about 300 more calories each day, compared to those in the 9-hour sleep group.
The researchers found that people in the restricted sleep group had up to a 9% increase in belly fat and an 11% increase in unhealthy belly visceral fat, which surrounds the organs deep inside the belly and has been strongly linked to heart disease and other conditions like Alzheimer's disease, stroke, and type 2 diabetes.
“Our findings show that shortened sleep, even in young, healthy and relatively lean subjects, is associated with an increase in calorie intake, a very small increase in weight, and a significant increase in fat accumulation inside the belly,” Virend Somers, MD, PhD, a researcher in cardiovascular and sleep medicine at the Mayo Clinic, says in a news release about the study.
The study authors say that poor sleep has been repeatedly linked with obesity, but theirs is the first study to link lack of sleep with body fat distribution.
Normally, fat is deposited just under the skin, Somers says, but a lack of sleep appears to redirect it to the deeper, more dangerous position around the organs. Catching up on sleep in the recovery period of the study did not reverse the accumulation of visceral fat, the researchers found, though study participants’ calorie intake and weight did decrease.
The findings, published in the Journal of the American College of Cardiology, are particularly important, according to the researchers, as more than one-third of adults in the U.S. don’t get enough sleep. Things that disrupt sleep include shift work and using smart devices and social networks during traditional sleep hours, the authors write.
Study leader Naima Covassin, PhD, an assistant professor of cardiovascular medicine at the Mayo Clinic, says in the news release that the researchers detected the growing visceral fat deposits in the people in the study only because they performed CT scans, which gave them detailed internal images. Those in the restricted sleep group only gained about a pound of weight.
“Measures of weight alone would be falsely reassuring in terms of the health consequences of inadequate sleep," Covassin says. "Also concerning are the potential effects of repeated periods of inadequate sleep in terms of progressive and cumulative increases in visceral fat over several years.”