Marceau K, et al. - Researchers analyzed associations across childhood between levels of sleep duration, BMI, and cortisol. Participants in the study were 361 children adopted domestically in the US. Findings suggested that the connection between sleep and BMI is more likely to be a stable phenomenon between individuals than a unidirectional association that develops over time within individuals. At 6 years of age, BMI predicted longer sleep duration and lower cortisol at 7 years of age; lower morning cortisol at 7 years of age predicted higher BMI at 9 years of age within individuals.