Academic performance, externalizing disorders and depression: 26,000 adolescents followed into adulthood

Background: The incidence of major depression among adults has been shown to be socially differentiated, and there are reasons to seek explanations for this before adulthood. In this cohort study, we examined whether academic performance in adolescence predicts depression in adulthood, and the extent to which externalizing disorders explain this association.
Methods: We followed 26 766 Swedish women and men born 1967-1982 from the last year of compulsory school, at age about 16, up to 48 years of age. We investigated the association between grade point average (GPA, standardized by gender) and first diagnosis of depression in national registers of in- or out-patient psychiatric care. We used Cox proportional hazards models, adjusting for lifetime externalizing diagnoses and potential confounders including childhood socioeconomic position and IQ.
Results: During follow-up, 7.0% of the women and 4.4% of the men were diagnosed with depression. A GPA in the lowest quartile, compared with the highest, was associated with an increased risk in both women (hazard ratio, 95% confidence interval: 1.7, 1.3-2.1) and men (2.9, 2.2-3.9) in models controlling for potential confounders. Additional control for externalizing disorders attenuated the associations, particularly in women.
Conclusions: The findings suggest that poor academic performance is associated with depression in young adulthood, and that the association is partly explained by externalizing disorders. Our results indicate the importance of early detection and management of externalizing disorders among children and adolescents.