Sleep and Adiposity in Preadolescent Children: The Importance of Social Jetlag.

Background: While short and poor quality sleep have been associated with childhood obesity, no known studies have examined social jetlag. Social jetlag is the discrepancy between an individual's circadian clock and social rhythms, and is measured as the difference in hours between the midpoint of sleep during work/school days and on free (weekend) days. This study investigated the independent associations between sleep duration, sleep disturbances, and social jetlag with adiposity in children. Methods: A cross-sectional study, including 341 children (50% female) aged 8-10 years. Five dependent variables: body fat (%), fat mass (kg), fat mass index (FMI, kg/m(2)), waist to hip ratio, and body mass index (kg/m(2)). Three independent variables: average sleep duration, sleep disturbances, and social jetlag. Results: Following adjustment for confounders, sleep duration was not associated with any variable, and sleep disturbances were associated with FMI (beta=0.047, 95% CI: 0.002, 0.093 kg/m(2)), while social jetlag was associated with all five adiposity variables, including an absolute 3% greater body fat (beta=2.963, 95% CI: 0.40, 5.53%) per 1 hour of social jetlag. Conclusions: Social jetlag may be an important and measurable public health target in children.