The Social Transmission of Mental Illness
Classmates' psychological disorders increase peers' later diagnosis risk
A recent paper in JAMA Psychiatry marshals evidence that mental illness can spread via social contagion among adolescents.
Drawing on data from more than 700,000 Finns, the paper shows that ninth-grade students who had one or more classmates with a mental illness were more likely to develop a mental illness themselves in subsequent years.
As the graph shows, the risk was particularly great in the immediate year after exposures. As it also shows, there was a dose-response relationship: People with two or more classmates with a mental illness were at a greater risk than those with only one.
More fine-grained analyses showed that the effect was particularly strong for depression, anxiety, and eating disorders.
A possible alternative explanation for the pattern is that people in the same class may commonly experience the same stressors, and that this increases the chances of several of them having psychological problems within a year or so of each other. To rule this out, the researchers statistically controlled for a range of family, school, and area-level variables plausibly associated with such stressors. The effect remained intact. That should raise our confidence at least a little that the social-contagion explanation is accurate.
If it is, what might be the mechanism of social transmission? Here’s an excerpt from the paper addressing that question.
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. Similarly, having individuals with no diagnosis in the peer network might discourage seeking help for any underlying mental health problems. The observed higher risks of being diagnosed during the first year of follow-up after the exposure are consistent with this mechanism. Namely, due to diagnostic delay, the brief latency between exposure and diagnosis challenges the likelihood of harmful contagion occurring without an already existing, undiagnosed disorder. For some diagnosis categories, such as eating disorders, transmission could also occur through processes of peer social influence to which adolescents are particularly susceptible. 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.
The paper is by Jussi Alho and colleagues. You can read the whole thing here.
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Really interesting data. I think normalisation of manifesting symptoms and help seeking is a good hypothesis (and for conditions where symptom IS the disorder, like EDs, this effect should be stronger).
There's also a possibility that having a classmate with psychiatric disorder is itself a stressor.
It'd be cool to see whether being aware of the diagnosis influenced this relationship and how.
And doing matched classes comparisons would provide extra control on top of controlling for certain variables.