A new study of more than 700,000 people living in Finland found that mental illnesses like depression, anxiety, and eating disorders could potentially be transmitted socially within adolescent peer groups.
“We found an association between having peers diagnosed with a mental disorder during adolescence and an increased risk of receiving a mental disorder diagnosis later in life,” the researchers wrote in the JAMA Psychiatry study that was published on May 22, 2024. “There was a higher risk when multiple diagnosed individuals were in the peer network. Of the mental disorders examined, the risk was greatest for mood, anxiety, and eating disorders.”
The team hypothesized that several mechanisms could be involved if mental disorders might be transmitted socially via peer groups. “One plausible mechanism is the normalization of mental disorders through increased awareness and receptivity to diagnosis and treatment when having individuals with diagnosis in the same peer network,” the authors explained.
For eating disorders, they noted that transmission might occur due to “processes of peer social influence to which adolescents are particularly susceptible.”
“It is (also) conceivable that long-term exposure to a depressive individual could lead to the gradual development of depressive symptoms through the well-established neural mechanisms of emotional contagion,” the authors added. Social psychologist Elaine Hatfield coined the term “emotional contagion” to describe how people observe and then unconsciously mimic the emotions and behaviors of the people they spend the most time with.
Lead author Jussi Alho from the University of Helsinki and colleagues analyzed the data of 713,809 Finnish citizens born between 1985 to 1997 that they had collected from nationwide registers. The team conducted follow-ups with the study participants soon after they completed the ninth grade at the age of 16 years in 860 schools across Finland. During each follow-up, they checked whether or not they were diagnosed with mental disorders and continued doing so until December 31, 2019.
Out of the 713,809 study participants, 47,433 were diagnosed with a mental disorder by the ninth grade. Another 25% or 167,227 people received a diagnosis of a mental disorder during the follow-up period.
Through their data analysis, 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 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 authors observed. “Diagnosis-specific analyses showed that 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,” they added. “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,” they added.
