Abstract

We investigated whether bedtime schedules and bedtimes in childhood were associated with obesity risk and adiposity in adolescence. We analysed the data of 12,645 singleton children classified as not obese at 7 years from the Millennium Cohort Study in the United Kingdom. Bedtimes and the regularity of bedtimes of 7-year-olds were reported by parents. Bio-electric impedance body fat percentage (BFP) measurements and obesity at 11 and 14 years were the considered outcomes. The International Obesity Task Force age- and sex-specific thresholds were used to define obesity. Obesity risk at 11 and 14 years was higher among children with never-regular bedtimes at 7 years compared with those with always-regular bedtimes (risk ratio, RR, 2.8 (95% CI, 1.8–1.4) and 2.3 (95% CI, 1.5–3.6), respectively). An increasing irregularity in childhood bedtime was associated with an increasing risk of obesity at both 11 and 14 years in a dose–response manner (p trend < 0.001; and p trend = 0.002, respectively). BFP at 11 years increased by 1.1% (95% CI, 0.8–1.5) for boys and 1.0% (95% CI, 0.6–1.4) for girls for every hour delay in childhood bedtime. Irregular bedtime schedules and later bedtimes in childhood were associated with an increased risk of obesity in early- and mid-adolescence in a dose–response manner. There was marginal, but significant, increases in BFP during adolescence for children with later bedtimes.