If you’re at all concerned about your teen’s weight, you may want to take a look at what time they are hitting the sack. The results of a new study show that staying up past bedtime can lead to an increased body mass index (BMI) in adolescents.

Researchers from The University of California, Berkeley analyzed bedtimes and BMI of 3,342 teenagers in data collected by the National Longitudinal Study of Adolescent Health between 1994 and 2009 and found that for every hour a teen stayed up past bedtime, there was a two-point increase in their BMI.

"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," said lead researcher Lauren Asarnow, a doctoral candidate at UC Berkeley.


What’s interesting is that the study found the link between late bedtimes and increased BMI was not affected by the total amount of sleep time, exercise and time spent in front of televisions and computers.  The study also doesn't prove that teens frequently staying up late are necessarily destined to be overweight, but by going to bed earlier, teenagers can “set their weight on a healthier course as they emerge into adulthood,” said Asarnow.

Of course it’s okay for a child to stay up later occasionally, but for the most part it doesn’t hurt for them to have a bedtime that’s consistently adhered to. The CDC recommends teenagers get between 8.5 and 9.5 hours of sleep a night, so if they have class at 8am, that would mean going to bed at 10pm to give them an hour to get ready and get to school.

Having a healthier diet while also avoiding caffeine at night are ways that can help prevent adolescents from staying up later.

What do you do to make sure your kids get to bed on time?



  1. CDC: Most US Middle and High Schools Start the School Day Too Early
  2. Sleep Journal: Evidence for a Possible Link between Bedtime and Change in Body Mass Index
  3. UC Berkeley: Late Bedtimes Could Lead to Weight Gain