Study: Teens with late bedtimes more likely to gain weight over time

U.S. teens are more sleep deprived than ever. Doctors say adolescents need 9 to 9 1/2 hours of sleep each night, but most are getting much less than that — closer to seven. Studies have shown the consequences can be devastating in this critical period of growth and include everything from lower academic performance to a higher risk of emotional distress.

There’s been movement in many school districts to get schools to start later to increase the amount of time teens can stay in bed, but the results of a new study suggest that this may not solve the sleep problem.

The study, published in the journal Sleep, found that bedtimes rather than duration of sleep may be linked to at least one health consequence: weight gain.

The researchers followed 3,342 adolescents from 1996 to 2009 and interviewed them three times during the study about bedtimes, exercise and food and television habits. They measured the volunteers’ heights and took weights to calculate body mass index during each of the check-ins.

They found that the later the average bedtime during the week, the higher the BMI over time. More precisely, they found that for every minute of later bedtime there was an increase in BMI of 0.035 kg/m2. Or for every additional hour later a 2.1 increase in BMI.

The results were significant even after they controlled for things such as gender, race and socioeconomic status.

“The results are important because they highlight adolescent bedtimes, not just total sleep time, as a potential target for weight management,” Lauren Asarnow, a doctoral candidate at the University of California at Berkeley and co-author of the study, said.