Researchers representing at the University of California, Berkeley, have found that teens and healthy adults who sleep late at night during weeknights are at higher risk of gaining weight than their peers who have the habit of sleeping on time. The study presenting the above results has been published in this month’s issue of the journal Sleep.

The study has further suggested that screen time, exercise and the number of hours one is sleeping cannot mitigate this increase in body mass index or BMI. For those who don’t know: an individual’s body mass index is obtained by dividing his/her weight in kilograms by the square of his/her height in meters. The BMI of a healthy adult should range between 18.5 and 24.9.

During the Berkeley study, researchers analyzed data offered by the National Longitudinal Study of Adolescent Health that has tracked the behaviors and influences of US teens since 1994. The researchers looked primarily at three phases, the start of puberty, the college-going age, and last, but not least young adulthood. They compared the BMI and bedtimes of American teenagers between 1994 and 2009.

It was found that adolescents who sleep early succeed in setting their body weight on a much healthier course as they enter adulthood. Each of the adolescents taking part in the study had to report their bedtimes. Their BMIs, however, were calculated by the researchers based on their body weight and height.

The researchers conducting the study examined longitudinal data presented by a nationally represented cohort study that had over 3,300 adults and youths as participants. They found that for each hour of sleep lost by those participants, there was an increase of 2.1 points in the BMI index. The researchers said that the weight gain typically takes place over a period of 5 years.

The study’s lead author Lauren Asarnow, a doctoral student at the Golden Beer Sleep & Mood Research Clinic of UC Berkeley, said that the results put forward by the study highlight the bedtime of adolescents, and not their overall sleep time, as a likely target for body weight management during shift to adulthood.

Asarnow is a part of the team carrying out the Teen Sleep Study at UC Berkeley. It’s a treatment program created for resetting biological clocks of adolescents who struggle to go to sleep and wake up.