A new study conducted in Finland suggests that mental disorders such as depression, anxiety, and eating disorders could potentially be transmitted socially within adolescent peer groups. The study, published in JAMA Psychiatry on May 22, 2024, analyzed the data of over 700,000 Finnish citizens born between 1985 to 1997. The researchers found that individuals who had peers diagnosed with a mental disorder during adolescence had an increased risk of receiving a mental disorder diagnosis later in life. The risk was especially high when multiple diagnosed individuals were in the peer network, particularly for mood, anxiety, and eating disorders.
The researchers hypothesized that several mechanisms could be involved in the social transmission of mental disorders within peer groups. One possible mechanism is the normalization of mental disorders through increased awareness and receptivity to diagnosis and treatment when individuals in the same peer network are diagnosed. For eating disorders, they noted that transmission might occur due to processes of peer social influence to which adolescents are particularly susceptible. Additionally, long-term exposure to a depressive individual could lead to the gradual development of depressive symptoms through emotional contagion.
Lead author Jussi Alho and his colleagues conducted follow-ups with the study participants who had completed the ninth grade at the age of 16 in 860 schools across Finland. They checked whether or not the participants were diagnosed with mental disorders and continued to do so until December 31, 2019. Out of the 713,809 study participants, 47,433 were diagnosed with a mental disorder by the ninth grade, and another 25% were diagnosed during the follow-up period. The researchers found that having more than one diagnosed classmate with mood, anxiety, behavioral, or eating disorders was associated with a 5% higher risk of a later diagnosis.
During the first year of follow-up, the risk of being diagnosed was 9% higher with one diagnosed classmate and 18% higher with more than one diagnosed classmate. The risk was significantly increased for mood, anxiety, and internalizing disorders in each follow-up time window, with the greatest risks observed during the first year. For example, having classmates with a mood disorder diagnosis was associated with a 32% higher risk of being diagnosed with a mood disorder during the first year of follow-up. The findings of this study are consistent with previous research showing clustering of mood and anxiety symptoms in social networks of adolescents and adults, as well as evidence suggesting similar social transmission of eating disorders.
