Poor peer relations in adolescence, social support in early adulthood, and depressive symptoms in later adulthood-evaluating mediation and interaction using four-way decomposition analysis.

Purpose: Supportive social relations are associated with good mental health, yet few studies have considered the prospective importance of adolescent peer relations for adult mental health and the potential mechanisms involved. Methods: Participants (n = 941) were sourced from the Northern Swedish Cohort, a prospective study comprising school students aged 16 years in 1981. Integrating life course epidemiology with four-way decomposition analysis, this paper considers the controlled direct effect of poor peer relations at age 16 years on depressive symptoms at age 43 years, the pure indirect effect mediated by the availability of social support at age 30 years, and potential interactions between the exposure and the mediator. Results: After controlling for gender, baseline depressive symptoms, and parental socioeconomic position, poor peer relations at age 16 years were associated with depressive symptoms at age 43 years, largely irrespective of social support at age 30 years. Nonetheless, poor peer relations in adolescence were associated with poorer social support at age 30 years, and mediation accounted for a modest proportion (pure indirect effect 10%) of the association between poor peer relations at age 16 years and depressive symptoms at age 43 years. Conclusions: Policies to foster constructive peer relations for adolescents at school are encouraged; such policies may promote both the availability of social support and better mental health across the life course. (C) 2018 Elsevier Inc. All rights reserved.