Lack of sleep could increase obesity in children and too much television could be partly to blame.

AIM: To examine the bidirectional relationship between short sleep duration and body mass index (BMI). A secondary aim was to investigate whether reduced physical activity and increased screen time (television and computer use) mediated these associations. METHODS: This study utilised data from the Longitudinal Study of Australian Children, which is an observational cohort study of Australian children. The sample included 2984 (52.4% boys) children followed from 4 to 5 years of age until 8 to 9 years of age. Sleep duration, screen time and covariates were reported by parents, with BMI measured objectively. Cross-lagged modelling investigated the bidirectional association between sleep duration and BMI; lagged panel mediation modelling examined physical activity and screen time as potential mediators. RESULTS: Short sleep duration at 4 to 5 years of age was significantly associated with higher BMI at 8 to 9 years of age (ß= -.07, p = .044). The relationship between short sleep duration at 4 to 5 years of age and higher BMI at 8 to 9 years of age was partially mediated by increased television viewing at 6 to 7 years of age (ß = -.01, 95% confidence interval [-.02, -.002]). CONCLUSION: Short sleep duration could be a risk factor for obesity in children. Increased television viewing may be one mechanism underlying this longitudinal relationship.