• Posted August 7, 2024

Your Friends' Genes May Harm or Help You

Remember your besties from high school? Sure, they made a lasting impression, but science suggests they influenced the trajectory of your health, too.

It's not that far-fetched: Your friends carry genes that may or may nor predispose them to mental health issues ranging from addiction to anxiety and depression. That can influence the mental health of the people in their friend circle, according to researchers at Rutgers University in New Jersey.

“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 study lead author Jessica Salvatore.

“What our data exemplifies is the long reach of social genetic effects,” she said in a Rutgers news release. Salvatore is an associate professor of psychiatry at the university.

It's a relatively new field of research called socio-genomics: How one person's genetic makeup ("genotype") can influence a wider network of people.

Just how powerful is the socio-genomic effect? To find out, Salvatore's group looked at Swedish data on over 1.5 million individuals born in Sweden between 1980 and 1998.

They then pinpointed exactly where everyone went to school in their teen years. That was followed up by a deep dive into local medical, pharmacy and legal registries that documented any history of substance use and mental health disorders for the same individuals in adulthood.

Sophisticated computer modeling was then used to assess whether the genetic predispositions of a person's peer group was associated with aspects of that person's mental health.

The result: Clear links were seen between a close friend's genetic predispositions and an individuals’ likelihood of developing a substance use or psychiatric disorder, the team reported.

The effects were stronger between people who went to school together versus simply growing up in the same locale, Salvatore's group added.

The researchers could even pinpoint which years were most crucial to the effect: A period between the ages of 16 and 19 for kids engaged in the same vocational or college-preparatory track in high school.

For school-based peers, the genetic effect was especially strong for drug and alcohol use disorders, the study found.

The findings were published Aug. 7 in the American Journal of Psychiatry.

According to Salvatore, tackling problems like drug abuse, anxiety and depression in youth may mean widening the focus beyond one individual.

“If we want to think about how to best address these socially costly disorders, we need to think more about network-based and social interventions,” she said.  “It’s not enough to think about individual risk.”

Salvatore stressed that the effects can last long after graduation day.

"Peer genetic influences have a very long reach,” she said.

More information

Find out about the genetic component of depression at Stanford University.

SOURCE: Rutgers University, news release, Aug. 7, 2024