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 4.5 to 9 years of age.
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.