Sleep Duration and Adiposity in Children and Adults: Observational and Mendelian Randomization Studies

Objective This study used two complementary designs, an observational and a Mendelian randomization (MR) study, to assess whether sleep duration causes adiposity in children and adults. Methods In Hong Kong's "Children of 1997" birth cohort, the adjusted cross-sectional associations of sleep duration with BMI z score and obesity and overweight were assessed at similar to 11 years of age. Generalized estimating equations were also used to examine longitudinal associations of sleep duration at similar to 11 years with annual BMI z score and obesity and overweight at about 11 to 16 years of age. Using MR, this study assessed the association of genetically predicted sleep duration, based on 54 single-nucleotide polymorphisms, applied to genetic studies of adiposity in children (n = 35,668), men (n = 152,893), and women (n = 171,977). Results Longer sleep was cross-sectionally associated with lower BMI z score at similar to 11 years of age (-0.13 per category, 95% CI: -0.22 to -0.04) and at about 11 to 16 years of age longitudinally in girls (-0.39, 95% CI: -0.66 to -0.13). Using MR, sleep duration was inversely associated with BMI in children (-0.29 SD per hour, 95% CI: -0.54 to -0.04), but was not clearly associated with BMI in adults, particularly for women. Conclusions A small beneficial effect of sleep on BMI in children cannot be ruled out.