A Finnish teen study suggests that mental disorders may be transmitted socially via peer networks, such that having friends who have a diagnosis of mental disorders may put adolescents at risk of receiving one themselves.
Nationwide, interlinked registry data involving 713,809 16-year-olds (50.4 percent male) showed a dose-response association between having a classmate with a mental disorder (eg, substance misuse, schizophrenia spectrum, mood, anxiety, eating, behavioural and emotional, and internalizing and externalizing disorders) and the risk of receiving a similar mental disorder diagnosis, the investigators reported.
Teens who had one classmate with a mental disorder were not at increased risk of receiving a similar diagnosis (hazard ratio [HR], 1.01, 95 percent confidence interval [CI], 1.00–1.02), but those who had at least two classmates with a mental disorder had a 5-percent risk increase (HR, 1.05, 95 percent CI, 1.04–1.06). [JAMA Psychiatry 2024;doi:10.1001/jamapsychiatry.2024.1126]
The risk was highest during the first year of follow-up, with a 9-percent increase for teens who had one classmate with a mental disorder (HR, 1.09, 95 percent CI, 1.04–1.14; p<0.001) and an 18-percent increase for those who had at least two classmates with a mental disorder (HR, 1.18, 95 percent CI, 1.13–1.24; p<0.001).
In diagnosis-specific analyses, the risk was significantly pronounced for mood, anxiety, and internalizing disorders, the investigators noted. For instance, the risk of being diagnosed with a mood disorder was 21 percent higher during the first year of follow-up among teens who have a classmate with a mood disorder (HR, 1.21, 95 percent CI, 1.13–1.29; p<0.001).
These associations, according to the investigators, were not explained by differences in area-level general morbidity or socioeconomic characteristics, parental mental disorders or socioeconomic position during childhood, or random differences in predisposition to mental health problems occurring among schools’ student populations.
“To our knowledge, the present study is the largest and most comprehensive investigation on this topic to date. Our findings are consistent with previous studies reporting clustering of mood and/or anxiety symptoms in social networks of adolescents and adults, as well as with evidence suggesting similar social transmission of eating disorders,” the investigators said. [Am J Sociol 2020;125:1513-1558; Psychiatr Ann 2023;53:228-235; Adm Sci Q 2022;67:1-48]
As to how mental disorders can be transmitted socially via peer networks, the investigators postulated that normalization of mental disorders can happen through increased awareness and receptivity to diagnosis and treatment when having individuals with diagnosis in the same peer network. Likewise, having individuals with no diagnosis in the peer network might discourage seeking help for any underlying mental health problems. [AJS 2010;115:1387-1434]
Transmission of some diagnosis categories, such as eating disorders, could also occur through peer social influence to which adolescents are particularly susceptible, the investigators pointed out. [Prev Med 2020;130:105900]
“Another possible mechanism facilitating the transmission of certain mental disorders, such as depression, pertains to direct interpersonal contagion. For instance, it is conceivable that long-term exposure to a depressive individual could lead to gradual development of depressive symptoms through the well-established neural mechanisms of emotional contagion,” they added. [Neurosci Biobehav Rev 2022;134:104509]
While further research is required to clarify the mechanisms that explain the observed associations, the present data underscore the need for prevention and intervention measures that consider potential peer influences on early-life mental health as a means to substantially reduce the disease burden of mental disorders in society.