Depression is an epidemic.  If you know someone who is suffering - and the chances are very much so that you do - there is something simple and beautiful that you can do to help. Simply be happy in their company. Far from worrying that your happiness might make things worse, it seems that joy is contagious, while depression is definitely not. A new study, published in Proceedings of the Royal Society B, found that one of the most effective boons to mental health is being surrounded by positive people. Researchers from the Universities of Manchester and Warwick studied 2,000 high school students. Using computer models to track their moods, scientists found that depressed moods don't spread from one person to another, while happy moods do. Study author Thomas House, Ph.D., senior lecturer in applied mathematics from the University of Manchester, said in a press release: "We know social factors—for example living alone or having experienced abuse in childhood—influence whether someone becomes depressed. We also know that social support is important for recovery from depression, for example having people to talk to." And it's a case of the more the merrier too - with adolescents who had five or more "healthy" friends in terms of mental status ended up with half the probability of being depressed. The teenagers who had 10 healthy friends also had twice the probability of recovering from a depression and the symptoms associated with it.