Sleeping too much or too little is associated with a higher prevalence of belly fat, according to a new study published this week in the journal SLEEP. The analysis of more than 1,000 blacks and Hispanics between the ages of 18 and 81 found that, in participants ages 40 and younger, sleeping fewer than five hours per night or more than eight hours per night was associated with higher concentrations of abdominal fat and increased body mass index (BMI) during the five-year study period compared with participants who slept six to seven hours per night. There was no correlation between sleep duration and belly fat among participants over age 40.
Body mass index, a measurement based on weight over height squared, is given in terms of kg/m2. In this study, subjects under age 40 who slept fewer than five hours had average BMI increase 1.8kg/m2 or more higher than those who slept six to seven hours. And participants who slept more than eight hours had average BMI increases 0.8kg/m2 higher than those who slept an hour or two less per night.
On average, those who slept the least consumed more calories per day (2,224) compared with those who slept six to seven hours per night (1,920 calories) or eight or more hours per night (2,199 calories). That excess intake, together with lower energy expenditure—caused by fatigue and lower levels of vigorous activity—are likely the ways in which shortened sleep is linked to increased belly fat, the researchers suggest.
The findings suggest that, in addition to emphasizing the importance of healthy eating and regular exercise, doctors also need to stress to patients the value of getting enough sleep toward maintaining overall health, the researchers conclude.