For teens, late bedtime may lead to weight gain

Teens may have a new reason to take their parents’ advice and go to bed early. Staying up late on weeknights may increase a teen’s risk of becoming overweight over time, a new study says.

For the study, researchers analyzed data from more than 3,300 American teens and found that each extra hour of late bedtime was associated with a more than two-point increase in body mass index (BMI). BMI is an estimate of body fat based on weight and height.

The link between late bedtimes and BMI increase was not significantly affected by total sleep time, amount of exercise, or time spent in front of computers or televisions, the investigators found.

“The results are important because they highlight adolescent bedtimes, not just total sleep time, as a potential target for weight management concurrently and in the transition to adulthood,” first author Lauren Asarnow, a doctoral candidate at the University of California, Berkeley, said in a news release from the American Academy of Sleep Medicine.

The study, published in the October issue of the journal Sleep, doesn’t prove that night owls are destined to be overweight, however. The findings only show an association between bedtime and weight, not a causeand-effect relationship.

Teens need a little more than nine hours of sleep a night, according to the American Academy of Sleep Medicine.