Losing weight, especially in the belly, improves sleep quality

"We found that improvement in sleep quality was significantly associated with overall weight loss, especially belly fat," says Kerry Stewart, Ed.D., professor of medicine at the Johns Hopkins University School of Medicine and director of clinical and research exercise physiology.

Stewart is the senior author of the study, which will be presented at the American Heart Association Scientific Sessions on November 6, 2012 by lead author Soohyun Nam, Ph.D., who is now at the Yale University School of Nursing. Her presentation is titled Predictors of Sleep Quality Improvement Among Overweight or Obese Individuals: A Randomized Controlled Trial.

For the six-month study, the researchers enrolled 77 people who had type 2 diabetes or pre-diabetes. The participants, all of whom also were overweight or obese, were randomly assigned to one of two groups. One group went on a weight-loss diet and had supervised exercise training, while the other group only had the diet intervention. A total of 55 participants completed all phases of the study.

The participants filled out the Hopkins Sleep Survey at the beginning and end of the study to identify sleep problems, including sleep apnea, daytime fatigue, insomnia, restless sleep, excessive sleep or sleepiness and use of sedatives to aid sleep. Their body mass index and amount of abdominal fat were also measured at the start and end of the study.

Both groups -- those assigned to a weight loss diet plus supervised exercise and those who only went on a diet -- lost about 15 pounds, on average. They also lost about the same amount of belly fat, about 15 percent, which was assessed by magnetic resonance imaging (MRI).

Although a variety of sleep problems were reported by the participants, none stood out as being the most common, so the researchers analyzed a composite score, which reflects overall sleep health. What they found was that both groups improved their overall sleep score by about 20 percent with no differences between the groups.

"The key ingredient for improved sleep quality from our study was a reduction in overall body fat, and, in particular belly fat, which was true no matter the age or gender of the participants or whether the weight loss came from diet alone or diet plus exercise," says Stewart.

Good sleep quality is important in general for good physical and mental health, as well as for a healthy cardiovascular system, notes Stewart. Depending on the cause, chronic sleep disruptions increase the risk of high blood pressure, heart attack, stroke and irregular heartbeats. Obesity increases the risk of sleep problems.

The study was funded by the National Heart, Lung, and Blood Institute, grant number R01HL092280 and the National Center for Advancing Translational Sciences, grant number UL1 RR 025005.