This study investigated the relationship between changes in chronotype and social jetlag and changes in body composition during adolescence. Using data from the DONALD study (213 adolescents, 9–17 years at baseline), the researchers found that a later chronotype and increased social jetlag were significantly associated with increased fat mass index (FMI) and BMI standard deviation scores (BMI-SDS). These associations were strongest in the 12–15-year-old age group. No significant association was found with fat-free mass index (FFMI). The findings suggest that the period between 12 and 15 years of age may be particularly sensitive to the effects of chronobiological changes on body fatness.
