Nighttime sleep duration trajectories were associated with body mass index trajectories in early childhood.

Background The respective contribution of total, daytime and nighttime sleep duration in childhood obesity remains unclear. Objectives To assess the longitudinal association between developmental trajectories of sleep duration and BMI z-score in early childhood. Methods Data were from the Melbourne INFANT program, a prospective cohort with 4-month-old infants being followed-up until age 60 months (n = 528). Sleep duration (total, daytime, nighttime) and BMI z-score were measured using questionnaire at ages 4, 9, 18, 43 and 60 months. Group-based trajectory modelling was used to describe longitudinal trajectories from ages 4 to 60 months. Multivariable logistic regression was conducted to assess the association between sleep duration and BMI z-score trajectories. Results Three nighttime sleep duration trajectory groups were identified: Long stable (10.5 to 11.0 hours, 61%), catchup (8.0 to 11.5 hours, 23%) and short stable (8.7 to 9.8 hours, 16%) nighttime sleepers. BMI z-score trajectory groups were classified as low-BMIz (-1.5 to -0.5 unit, 21%), mid-BMIz (-0.5 to 0.5 unit, 58%) and high-BMIz (0.8 to 1.4 unit, 21%). With adjustment for child and maternal covariates, both catchup (OR 3.69 95%CI 1.74, 7.92) and long stable nighttime sleepers (OR 4.27 95%CI 2.21, 8.25) revealed higher odds of being in the mid-BMIz than the high-BMIz group. By contrast, total or daytime sleep duration trajectories were not associated with BMI z-score trajectories. Conclusions Longer nighttime, but not total or daytime, sleep duration was associated with lower BMI z-score trajectories in early childhood. Our findings reinforce the importance of nighttime sleep for healthy body-weight development in early childhood.