Does later chronotype cause poorer adolescent mental health? An Adolescent Brain Cognitive Development (ABCD) Study.

Objective: This study investigated whether chronotype (biobehavioral preference for sleep and wake timing) across early adolescence impacts mental health symptoms at age 13-14. This is a relationship with growing correlational evidence but limited causal exploration. Methods: Participants were 7,489 adolescents (aged 9-10 at baseline; 13-14 at the fifth assessment wave) from the Adolescent Brain Cognitive Development Study (ABCD). Marginal structural models with machine learning-based weight estimation were used to assess the causal impact of chronotype at ages 11-12 and 12-13, as measured by the youth-reported Munich Chronotype Questionnaire, on several dimensions of mental health symptoms at age 13-14 (parent-reported Child Behavioral Checklist internalizing and externalizing values; child-reported Prodromal Psychosis Scale). Results: There was no effect of chronotype at age 11-12 on any outcome. However, later chronotype at age 12-13 was associated with more severe externalizing symptoms (b=.31, p=.02) and prodromal psychosis symptoms at age 13-14 (b=.06, p<.01), but not with more severe internalizing symptoms. Post-hoc analyses indicated the lack of relationship with internalizing held for both anxiety and depression symptoms and in both sexes. Conclusions: There are likely causal effects of adolescent chronotype on mental health symptoms, but these are dependent on the dimension of mental health and period of adolescence. The typically-reported association between later chronotype and more severe internalizing symptoms may not manifest until later adolescence (such as with the common post-pubertal shift in chronotype).