Abstract
BACKGROUND AND OBJECTIVE: Short night-time sleep duration is a possible factor contributing to childhood obesity. Our objective was to evaluate associations between sleep timing (including bedtime and waketime) and weight gain in 4- to 5-year-old children. METHODS: We used cross-sectional and longitudinal regression analyses of a large, nationally representative sample of children from the Early Childhood Longitudinal Study-Birth Cohort. Data regarding the timing and duration of weekday sleep were assessed via parent questionnaire. Short sleep duration, late bedtime and early waketime were defined as those greater than one standard deviation from the mean for the group. RESULTS: Using linear regression adjusted for confounders, sleep duration at 4 and 5 years and bedtime at 5 years were linked to body mass index (BMI) z-score (P < 0.001). Odds of obesity were higher at 4 years for children sleeping <9.44 h nightly (adjusted odds ratio 1.35, confidence interval 1.02-1.78, P < 0.05) and at 5 years for children going to bed at 9:00 pm or later (1.49, 1.16-1.45, P < 0.01) or waking before 6:30 am (1.23, 1.01-15.51, P < 0.05). Assessed longitudinally, both short sleep duration (P < 0.05) and later bedtime at 4 years (P < 0.01) were associated with increases in BMI z-score between 4 and 5 years. CONCLUSIONS: Children with shorter night-time sleep durations and later bedtimes were more likely to be obese and to gain weight over time. Pediatricians should encourage families to place children to bed at earlier times to promote longer sleep duration as a potential means of controlling weight gain.