Friendships during teen years can make or break mental health. It's not just about the support they provide during tough times that the researchers are talking about, but how their genetic traits can affect you. The traits of your friends, particularly their genetic predisposition to mental health issues, can influence your mental health risks, a recent study revealed.

Socio-genomics is a topic of growing interest that investigates the influence of a person's genotype on the observable traits of another. The study published in the American Journal of Psychiatry investigated the peer's social genetic effects and found that a person's genetic predisposition to addiction, anxiety, and depression can have long-term consequences for their adolescent peers, affecting their risk of developing similar mental health issues later in life.

"Peers' genetic predispositions for psychiatric and substance use disorders are associated with an individual's own risk of developing the same disorders in young adulthood," said Jessica E. Salvatore, lead author of the study in a news release.

"What our data exemplifies is the long reach of social genetic effects," Salvatore said.

The study was based on a database of more than 1.5 million people born in Sweden between 1980 and 1998. The researchers first mapped individuals by location and school during their teenage years. They then examined medical, pharmacy, and legal records to track substance use and mental health disorders into adulthood. Using models they tested if peers' genetic risks predicted an individual's risk of experiencing substance abuse, major depression, or anxiety. Peer genetic risks were assessed using family genetic risk scores for the same conditions.

"Even when controlling for factors such as the target individuals' own genetic predispositions and family socioeconomic factors, the researchers found a clear association between peers' genetic predispositions and target individuals' likelihood of developing a substance use or psychiatric disorder. The effects were stronger among school-based peers than geographically defined peers," the news release stated.

The researchers noted that these links were most noticeable among upper secondary school classmates, particularly those in the same vocational or college-preparatory track between ages 16 and 19. The peer's genetic impact was greater for issues such as drug and alcohol use disorders compared to major depression and anxiety disorders.

"The most obvious explanation for why peers' genetic predispositions might be associated with our own well-being is the idea our peers' genetic predispositions influence their phenotype, or the likelihood that peers are also affected by the disorder. But in our analysis, we found that peers' genetic predispositions were associated with target individuals' likelihood of disorder even after we statistically controlled for whether peers were affected or unaffected," Salvatore said, adding that more research is needed to understand the mechanism.

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