Adolescents with a later bedtime during the week are more likely to experience an increase in body mass index (BMI) over time with fast-food consumption as a partial mediator, according to the first study to assess the relationship between bedtime and BMI longitudinally in an observational study.

Published in the journal Sleep, this research examined data from from the National Longitudinal Study of Adolescent Health on 3,342 adolescents between 1994–2009 on sleep/circadian variables (self-report measures of workday bedtime and sleep duration), height, weight, and the potential partial mediators of fast-food consumption, television viewing, and exercise.

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A later bedtime during the workweek from adolescence to adulthood was associated with an increase of 2.1 kg/m2 BMI for each additional hour of later bedtime. This was statistically significant after controlling for demographic characteristics and baseline BMI; fast-food consumption was the only significant partial mediator of those studied.

Based on these findings the authors concluded that adolescent bedtimes could be a potential target for weight management, concurrently and in the transition to adulthood.

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