Objective. The primary objective of this paper was to examine associations between sleep duration, body mass index (BMI), and cortisol levels across childhood.
Methods: Participants included 361 children adopted domestically in the United States. Random-intercept cross lagged panel models tested for between- and bi-directional within-person associations of sleep duration, BMI, and morning and evening cortisol from age 4.5 to 9 years.
Results: Sleep duration and BMI were stable during childhood, inversely associated at the between-person level, and unrelated to morning or evening cortisol. BMI at 6 years predicted longer sleep duration and lower evening cortisol at 7 years, and lower morning cortisol at 7 years predicted higher BMI at 9 years, within individuals.
Conclusions: The association between sleep and BMI is more likely a stable between-person phenomenon, rather than a unidirectional association that develops within-individuals over time.