How long you sleep may affect how much weight you carry around, according to a new report.

Researchers at the Walter Reed Army Medical center tracked the sleep, activity and weight of 14 nurses in a heart health program. They got diet counseling, exercise training and other education. They wore devices that tracked their activity.

Dr. Arn Eliasson, who led the study, said those considered short sleepers had an average BMI of 28.3. Long sleepers had a lower average BMI, 24.5.

When BMI hits 25, a person is considered overweight.

The researchers also found that those who were overweight tended to be more active than others, taking more steps and expending more calories.

Eliasson said it may be that getting less sleep upsets hormone balances leading to more weight gain. Or it could be that stress causes the weight gain and makes it harder to sleep.

He said he plans more studies to find out what causes the relationship between sleep and weight.