Changes in chronotype and social jetlag during adolescence and their association with concurrent changes in BMI-SDS and body composition, in the DONALD Study

BACKGROUND/OBJECTIVES: Adolescence is a critical period for both the development of overweight and the transition toward a later chronotype, often accompanied by an increase in social jetlag. This study assessed whether changes in chronotype and social jetlag are linked to changes in body composition during adolescence. SUBJECTS/METHODS: We used data from the DONALD open cohort study (2014–2019) from 213 adolescents (9–17 years at baseline, 45% female) with at least two measures of chronotype and anthropometry (N=572). Chronotype was assessed with the Munich Chronotype Questionnaire as the midpoint of sleep corrected for sleep debt (MSFsc); social jetlag (SJL) was the difference between mid-sleep on workdays and free days. Fat Free Mass Index (FFMI) and Fat Mass Index (FMI) were calculated from body fat percentage, weight, and height. Associations were analyzed using linear mixed-effects regression models; analyses were also stratified into three age groups (<12, ≥12 to ≤15, >15 years). RESULTS: Median follow-up was 2.1 years. Overall, a change toward a later chronotype was significantly related to an increase in FMI (β: 0.05, 95% CI: 0.01–0.08). A 1-hour increase in SJL predicted an increase in BMI-SDS of 0.08 (95% CI: 0.01–0.14) and in FMI of 0.04 kg/m² (95% CI: 0.003–0.08). Associations were stronger for the age group ≥12 to ≤15 years (p for interaction <0.001). No relationship was found with FFMI. CONCLUSIONS: Changes in MSFsc and SJL during adolescence were associated with concurrent changes in BMI-SDS and FMI. The age ≥12 to ≤15 years appears to be a sensitive period in which chronobiological changes were clearly associated with increasing body fatness.