Late bedtimes for teens could lead to weight gain over time

The team from Berkeley examined longitudinal data from a nationally representative cohort of more than 3,300 youths and adults, and found that for every hour of sleep they lost, they gained 2.1 points on the BMI index roughly over a 5-year period – not good.

Somewhat surprising to the researchers was the finding that the link between bedtime and BMI was not significantly impacted by exercise, computer screen time, or total sleep time. Specifically, the findings show that teens who go to bed late on weeknights are more likely to gain weight compared to those who go to sleep earlier.

Asarnow said that it’s important because it highlights “adolescents bedtimes, not just total sleep time; as a potential target for weight management concurrently and in the transition to adulthood”. “So, you’re more likely to gain weight going to bed at 2 a.m. then you are at 9 p.m., regardless of how much sleep you’re getting”, said Study Author Lauren Asarnow. BMI is an estimate of body fat based on weight and height. “For example, a woman who weighs 140 pounds and is 5′ 5” tall may gain 12 pounds due to sleeping late, causing her to become overweight.

The study analyzed data from the National Longitudinal Study of Adolescent Health, which has tracked the influences and behaviors of teenagers in the United States since 1994. “So even a two-point increase could be clinically significant”.

Published in the October issue of the journal Sleep, the study also surprisingly showed that the actual bedtimes versus number of hours the adolescents slept was a big factor.

The reason late bedtimes and BMI are linked is still to be determined, but so far scientists think it could be a combination of both metabolic and behavioral patterns. Individuals who prefer to sleep late at night gain more weight than their peers who sleep early.

This is confirmed by surveys in which teens report that they do not get the recommended nine hours of sleep a night, and report having trouble staying awake at school. Between 45% and 80% of those in this age group get inadequate rest due to extracurricular involvement, part-time jobs, excessive study load and late-night socializing. They sometimes keep up late and sleep in late on the weekends, which might have an effect on their organic clocks and damage the standard of their sleep.