Longitudinal associations between reported sleep duration in early childhood and the development of body mass index, fat mass index and fat free mass index until age 7

Objective. Epidemiological studies in children and adolescents have revealed short sleep duration as a risk factor for weight gain. However, only few studies have addressed sleep in early childhood. Our aim was to determine whether sleep in the second year of life is associated with the development of body composition throughout childhood. Methods. Analysis included 481 DONALD participants with parental reported data on sleep duration and annually measured body composition until age 7. Using median splits of sleeping time at 1.5 and 2 years we defined sleep duration categories: consistently short (CS, n = 122), inconsistent (I, n = 143) and consistently long (CL, n = 216). Polynomial mixed effects regression models were used to analyze differences in the trajectories of body mass index (BMI, kg/m(2)), fat mass index (FMI, kg/m(2)) and fat free mass index (FFMI, kg/m(2)) from ages 2-7 years between the sleep duration categories. Results. Compared to CL-children, CS-sleepers differed in their FMI development with respect to linear, quadratic and cubic trend (all p < 0.04), resulting in progressively higher FMI levels until age 7 independently of early life or socioeconomic factors. Trajectories of BMI and FFMI did not differ between the sleep duration categories. Conclusion. Consistently short sleep duration in the critical window of early childhood appears to exert a moderate but sustained adverse effect on the development of fat mass - but not fat free mass - until age 7.