Association of nighttime sleep duration at 1.5 years with height at 3 years: The Japan Environment and Children's Study.

CONTEXT Adequate nighttime sleep duration has been considered beneficial for linear growth in children; however, there is limited and conflicting evidence regarding the association between sleep duration and subsequent linear growth. OBJECTIVE To investigate the association between sleep duration at 1.5 years and height at 3 years of age. METHODS The Japan Environment and Children's Study is a nationwide prospective birth cohort study. Data from 52,140 term singleton births born at an appropriate-for-gestational age without background disorders that could potentially affect linear growth in the analyses were included. Nighttime and total sleep durations were calculated based on a self-administered questionnaire completed by caregivers. Tall stature was defined as height at or above the 75th percentile among participants. RESULTS After adjustment for height at 1.5 years, sex, monthly age, mother's height, presence of siblings at 1.5 years, environmental tobacco smoke at 1.5 years, daily TV/DVD screen time at 2 years, attendance at nursery at 2 years, household annual income at birth, and parents' educational status, multivariate odds ratio (95% confidence interval) for tall stature at 3 years were 1.09 (1.01-1.17), 1.09 (1.01-1.17), and 1.25 (1.14-1.37) for 9.5 or 10, 10.5 or 11, and ≥ 11.5 h of nighttime sleep duration at 1.5 years, respectively, compared with those with ≤ 9 h sleep (p for trend <0.0001). Total sleep duration was not associated with tall stature. CONCLUSION This study underscores the importance of nighttime sleep duration, not total sleep duration, in the linear growth of very young children.