A new study suggests that adolescent obesity could be decreased if teenagers got more sleep, and the heaviest would benefit most.

For a study published last week in Pediatrics, researchers surveyed 1,429 ninth graders, gathering data on height and weight. The children reported their sleep habits on weekdays and weekends to the nearest 15 minutes. The researchers followed the students with interviews every six months over the next four years, updating their data.

Each additional hour of sleep was associated with a reduction in body mass index, but the heaviest children — those above the 90th percentile of B.M.I. — had the greatest benefit, an average 0.28 reduction in B.M.I. for every extra hour. The researchers controlled for physical activity, screen time, sex, race and socioeconomic status.

The authors acknowledge that they had no data on caloric intake, which may increase with less sleep, but it is also possible that less sleep discourages physical activity and affects hormones that regulate energy expenditure.

“Our data can’t tell you what will happen with an individual child,” said the lead author, Jonathan A. Mitchell, a postdoctoral fellow at the University of Pennsylvania. “But based on our observational study, we predict that increasing the duration of sleep to 10 hours from eight would lead to a 4 percent reduction in obesity among U.S. children.”