Meera Senthilingam for CNN
Editor's note: Vital Signs is a monthly program bringing viewers health stories from around the world
(CNN) -- For teenagers, surrounding themselves with friends -- particularly friends in a good mood -- could significantly reduce their risk of developing depression, and improve their ability to recover from it.
In a study published this week, scientists analyzed the data of more than 2,000 high school students in the United States to investigate whether the moods of students influenced one another and if this could in turn impact levels of depression among teens. The teams modeled the spread of moods among the students over six to 12 months, using techniques similar to modeling the spread of an infectious disease.
"We classified people as ill (depressed) or not and looked at how that changed over time," says Thomas Moore, a lecturer in applied mathematics at the University of Manchester, who worked on the study.
Moore says previous studies have found depressed people tend to group into clusters, implying that this frame of mind could be spread. But the team found the opposite.
"Depression itself doesn't spread, but a healthy mood actually does," he says. The study found that teens with a strong group of friends not suffering from depression -- described as a "healthy" mood -- had half the probability of developing depression and double the probability of recovering if they were depressed.
"The effect was big, much bigger than you see form antidepressants," says Moore.
Importantly, depressed friends didn't counter the effect. "They don't seem to drag their friends down," says Moore.
The data was taken from the ongoing National Longitudinal Study of Adolescent to Adult Health currently taking place in the United States and the team see the findings as a useful weapon in the fight against depression -- particularly among teens.
According to data from the National Survey on Drug Use and Health in the United States, an estimated 2.6 million 12 to 17-year-olds had at least one major depressive episode during 2013. This represented 10.7% of the U.S. population aged 12 to 17.
"Depression is a major public health concern worldwide," says professor Frances Griffiths, head of social science and systems in health at Warwick Medical School, who also worked on the research. "Our results offer implications for improving adolescent mood ... that encouraging friendship networks between adolescents could reduce both the incidence and prevalence of depression among teenagers."
Whilst the study found a difference over six to 12 months, Moore believes the change could happen sooner. "We only got these two snapshots [of time]," he says.
Moore sees social activities such as youth groups as low-cost, low-risk options to help alleviate the burden of depression today. "If you combine this with other things known to work, they might work even better," he says.
Current treatment for depression is complex using combinations of therapy and drugs such as antidepressants as well as encouraging a healthy lifestyle.
"When we think of staying healthy, we often think of taking exercise and eating a healthy diet. However, we should also make time for our friendships as part of a healthy lifestyle," says Jim Bolton, a Fellow of the Royal College of Psychiatrists, in the United Kingdom.
"This study is additional evidence of the importance of friends and family in maintaining good mental health ... [and] importantly, this study indicates that when we do speak to family and friends our depression is not 'infectious,'" he says.
But he findings may not automatically apply to all teenage populations warns Shirley Reynolds, professor of evidence-based psychological therapies at the University of Reading. "These data are certainly intriguing and if replicated and substantiated have important implications for public health and social [or] educational interventions," she says. "However, there is no information given about the young people who took part ... this makes it impossible to know if they are representative of other teenagers in the USA, let alone teenagers in the UK or Europe."
Justin T. Baker, instructor of psychiatry at Harvard Medical School and a psychiatrist at McLean Hospital, in Belmont, Massachusetts, says it's a clever study, but cautions that it has several limitations. One is that it infers a "transmission model" from just two time points -- 6 and 12 months.
"Also, the authors chose to label participants as either depressed or not, even though mood and depression vary continuously along a continuum," he says. "This all-or-none label makes some sense for infection, but doesn't capture the experience of depression."
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