Sad friends will not bring you down but upbeat moods are contagious, a British study has shown.
Researchers at the universities of Manchester and Warwick studied 2,000 teenagers to see if their social groups could influence how they felt about life. They found that having mentally stable, happy friends helped to improve the mood of those who were depressed. But depressed people did not seem to have an impact on the state of mind of those around them.
The research team employed statistical methods usually used to monitor infectious diseases to find out how mood spread through social networks.
The results suggest that all friendships between teenagers can reduce depression since having depressed friends does not put them at risk, but having healthy, happy friends is protective and curative.
"This was a big effect that we have seen here," said Dr Thomas House, senior lecturer in applied mathematics from the University of Manchester.
"It could be that having a stronger social network is an effective way to treat depression. It may be that we could significantly reduce the burden of depression through cheap, low-risk social interventions."
Edward Hill, an applied mathematician, collaborated on the study, which was published in the journal Proceedings of the Royal Society B. He said: "We've ensured that the method we used was not confounded by homophily - that's the tendency for people to be friends with others like themselves."