Scientists used a mathematical model to find out if depression spreads from friend to friend. Depression isn’t catching, they find, but happiness may be.
The study shows that having friends can help teenagers recover from depression or even avoid becoming depressed in the first instance.
“Depression is a major public health concern worldwide. But the good news is we’ve found that a healthy mood amongst friends is linked with a significantly reduced risk of developing and increased chance of recovering from depression,” says professor Frances Griffiths, head of social science and systems in health at Warwick Medical School, University of Warwick.
“Our results offer implications for improving adolescent mood. In particular, they suggest the hypothesis that encouraging friendship networks between adolescents could reduce both the incidence and prevalence of depression among teenagers.”
High School Moods
Using data from the National Longitudinal Study of Adolescent to Adult Health, they looked at more than 2,000 adolescents in a network of U.S. high school students. They examined how teenagers’ moods influenced each other by modeling the spread of moods using similar methods to those used to track the spread of infectious diseases.
Individuals were classified as either having depressive symptoms (low mood) or not being depressed (healthy mood) according to the score cut-off associated with a clinical diagnosis of depression.
The team found that while depression does not “spread,” having enough friends with a healthy mood can halve the probability of developing, or double the probability of recovering from, depression over a 6 to 12-month period.
10 Happy Friends
The mathematical model suggests that adolescents who have five or more mentally healthy friends have half the probability of becoming depressed compared to adolescents with no healthy friends. And teenagers who have 10 healthy friends have double the probability of recovering from depressive symptoms compared to adolescents with just three healthy friends.
“In the context of depression, this is a very large effect size. Changing risk by a factor of two is unusual,” says lead author Edward Hill, a mathematics researcher at the University of Warwick.
“Our results suggest that promotion of any friendship between adolescents can reduce depression since having depressed friends does not put them at risk, but having healthy friends is both protective and curative.”
“As a society, if we enable friendships to develop among adolescents (for example providing youth clubs), each adolescent is more likely to have enough friends with healthy mood to have a protective effect. This would reduce the prevalence of depression.”
The study appears in the Proceedings of the Royal Society B.