Turns out your parent’s advice about choosing high school friends wisely was spot on.
A new study has found that your friends’ genetic traits can impact your own risk of developing mental health issues and substance use disorders.
The study published Wednesday in the American Journal of Psychiatry found that a peer’s genetic predispositions for psychiatric and substance use disorders are linked with an individual’s own risk of developing the same disorders in young adulthood.
“Certainly, this is something that as parents, when you think, ‘Who is my kid affiliating with?’ Those concerns are very valid,” said Jessica Salvatore, lead author and associate professor of psychiatry at the Rutgers Robert Wood Johnson Medical School, in New Brunswick, N.J.
“What we’re showing here is that above and beyond our own genetic predispositions, the genetic makeup of the people we are surrounded by matters,” she told Global News.
It is known that genetic predispositions play a critical role in the etiology of common psychiatric conditions, including drug and alcohol use disorders, major depression, and anxiety disorder, the authors argue.
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Previous research has shown that genetic traits can influence those around an individual, a phenomenon known as socio-genetics, where one’s genes interact with and are shaped by their social environment. Building on this, the authors aimed to understand how the genetic predispositions of high school peers impact an individual’s mental health and substance use outcomes.
To find this link, the authors partnered with Lund University in Sweden and used Swedish national data to assess peer social genetic effects for several psychiatric disorders.
With a database of more than 1.5 million individuals born in Sweden between 1980 and 1998, the authors first mapped individuals by location and school during their teenage years. They then used medical, pharmacy and legal registries documenting substance use and mental health disorders for the same individuals in adulthood.
Models were then used to determine if the genetic predispositions of peers could predict an individual’s risk of developing substance abuse, major depression and anxiety disorders in adulthood.
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Within school groups, the strongest effects were among upper secondary school classmates, particularly those in the same vocational or college-preparatory track between ages 16 and 19.
The study also found that school peers were stronger predictors of substance use disorder compared with anxiety disorder and major depression.
The impact of social genetic effects on disorder development varied based on an individual’s genetic predisposition. People with a higher genetic susceptibility were more likely to develop a disorder when exposed to peers with high genetic predispositions, though this effect was relatively small.
“Our findings provide strong evidence that social genetic effects are an important etiological factor in the development of common substance use disorders and to a lesser extent major depression and anxiety disorder, above and beyond one’s own genetic predispositions,” the study said. “Individuals with high-risk genetic predispositions may be especially sensitive to the impact of social genetic influences.”
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