Happiness is contagious, but depression doesn't rub off on you, according to a new study out of England. Researchers examined data from the National Longitudinal Study of Adolescent to Adult Health to study the moods of some 2,000 American high school students, according to a press release. By employing modelling akin to that used to chart the spread of infectious diseases, they found that depression does not spread, but having happy friends can alleviate or prevent depressive symptoms. "Our results offer implications for improving adolescent mood," says author Frances Griffiths of the University of Warwick. "In particular they suggest the hypothesis that encouraging friendship networks between adolescents could reduce both the incidence and prevalence of depression among teenagers."
The "contagious" property of happiness is actually quite significant statistically. "Adolescents with five or more healthy friends have half the probability of becoming depressed over a six- to 12-month period compared with adolescents with no healthy friends, and that adolescents with 10 healthy friends have double the probability of recovering from depressive symptoms over a six to 12-month period compared with adolescents with three healthy friends," according to the study, published in the Proceedings of the Royal Society B. The researchers end on this kicker: "If such an effect were demonstrated in an intervention study, this would massively outperform existing interventions." Another author gives that some context: "Changing risk by a factor of two is unusual," he says. (This teen pretended to be a friend and saved a life.)