A cohort study published in JAMA Psychiatry has identified a significant association between peer networks in adolescence and the transmission of mental disorders. Students with classmates diagnosed with mental disorders in ninth grade have up to an 18% higher risk of developing similar conditions later in life, according to a recent study.

This research analyzed data from over 700,000 individuals in Finland to determine whether having classmates with mental disorders in the ninth grade is associated with an increased risk of mental disorder diagnosis later in life.

The analysis of nationwide interlinked registry data revealed that students with classmates diagnosed with mental disorders had a higher likelihood of receiving a mental disorder diagnosis themselves. This increased risk remained significant after adjusting for various confounders, including parental mental health, school-level variables, and area-level factors. The highest risk was observed in the first year after exposure, with a 9% increase in risk for having one diagnosed classmate and an 18% increase for having more than one diagnosed classmate.

Study participants were followed from the completion of ninth grade (approximately age 16) until a mental disorder diagnosis, emigration, death, or the end of the study on December 31, 2019. The study found that the risk of developing mood, anxiety, and eating disorders was particularly elevated among those exposed to peers with mental health diagnoses.

“These findings suggest that mental disorders may be transmitted within adolescent peer networks,” the researchers concluded.

The authors declared having no competing interests.