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

ObjectiveThis study aimed to examine associations between sleep duration, BMI, and cortisol levels across childhood.MethodsParticipants 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.ResultsSleep 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.ConclusionsThe association between sleep and BMI is more likely a stable between‐person phenomenon rather than a unidirectional association that develops within individuals over time.