Longitudinal Associations of Sleep Duration, Morning and Evening Cortisol, and BMI During Childhood

Objective: This study aimed to examine associations between sleep duration, 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-person and bidirectional within-person associations of sleep duration, BMI, and morning and evening cortisol at 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 age 6 years predicted longer sleep duration and lower evening cortisol at age 7 years, and lower morning cortisol at age 7 years predicted higher BMI at age 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.