Adolescent Mental Health Risks May Be Transmitted Through Social Networks and Peer Interactions, Finnish Study Suggests
Finland: A study based on data from Finland provides evidence that the risk of mental health disorders may be transmitted among adolescents through social networks and peer interactions. The findings suggest that exposure to peers with mental health conditions could influence the likelihood of developing similar disorders, highlighting the importance of social environments in adolescent mental health and the need for early, community-based interventions.
The findings are from a nationwide cohort study published in JAMA Psychiatry by Jussi Alho from the Department of Psychology, Faculty of Medicine, University of Helsinki, Helsinki, Finland, and colleagues. The researchers investigated whether adolescents exposed to peers with diagnosed mental disorders or a higher inherited susceptibility to psychiatric conditions were at greater risk of developing mental disorders later in life.
For the study, the researchers analyzed nationwide registry data from 604,819 Finnish residents born between 1985 and 2000. Participants were assigned to four peer network settings—lower secondary schools, upper secondary schools, residential postal code areas, and neighborhood grids—and were followed from age 17 until a first mental disorder diagnosis, death, emigration, or December 31, 2023.
The researchers evaluated exposure to peers' family-based genetic risk for mental disorders and peers' own diagnosed mental disorders, while adjusting for participants' genetic risk, parental socioeconomic factors, sex, birth year, and peer network size.
Key findings:
- Over a median follow-up of 11.7 years, 234,117 of the 604,819 adolescents were diagnosed with at least one mental disorder.
- Higher genetic susceptibility among peers was associated with an increased risk of adolescents developing the same mental disorder later in life across multiple peer settings.
- The strongest association for peer genetic predisposition was observed for externalizing disorders in upper secondary schools, where the risk increased by 34%.
- Adolescents exposed to peers with diagnosed mental disorders were more likely to develop psychiatric disorders themselves.
- The association between peers' diagnoses and later mental disorders was strongest for internalizing disorders, such as anxiety and depression, in upper secondary school settings.
- Cross-disorder associations were also identified, with peers' genetic predisposition for externalizing disorders linked to later internalizing disorders in adolescents, and vice versa.
- These associations remained significant even after adjusting for adolescents' own genetic predisposition and parental socioeconomic status, suggesting that peer environments may independently influence mental health risk.
The researchers acknowledged several limitations, including possible incomplete registry data that may have missed undiagnosed or untreated individuals, modest observed associations, potential influence of unmeasured factors such as friendship selection, and limited generalizability of the findings beyond Finland's universal healthcare and education systems.
Overall, the study suggests that peer environments, particularly in upper secondary schools, may influence adolescents' future mental health. The researchers called for further studies to clarify the underlying mechanisms and inform school-based preventive interventions.
Reference:
Alho J, Gutvilig M, Niemi R, et al. Adolescent Peers' Diagnoses and Genetic Predispositions and Subsequent Risk of Mental Disorders. JAMA Psychiatry. Published online July 01, 2026. doi:10.1001/jamapsychiatry.2026.1752
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