Researchers suggest that prevalent moods in groups of adolescent friends are 'contagious.'
According to the latest data available to the National Institute of Mental Health, approximately 3 million adolescents aged between 12 and 17 in the United States had at least one major depressive event between 2014 and 2015.
But although cases of diagnosed depression are reaching worrying numbers worldwide - the World Health Organization (WHO) estimate that around 300 million people are affected worldwide - many people, and especially adolescents, exhibit depressive symptoms that are just under the threshold for a clinical depression diagnosis.
This is called "subthreshold depression," and the fact that it is not a clinical condition means that many people do not get the support that they need, despite often reporting a poor quality of life.
Now, researchers from the University of Warwick in Coventry, United Kingdom, are looking at how adolescents' social circles can influence their moods, in an effort to better understand what determines depressive symptoms among teenagers and what might alleviate them.
Robert Eyre, a doctoral student at the Complexity Science Doctoral Training Centre at the University of Warwick, led this study.
"We investigated whether there is evidence for the individual components of mood (such as appetite, tiredness, and sleep) spreading through U.S. adolescent friendship networks," Eyre explains, "while adjusting for confounding [factors] by modeling the transition probabilities of changing mood state over time."
"Evidence suggests mood may spread from person to person via a process known as social contagion."
Their findings were recently published in the journal Royal Society Open Science.
Prevalent moods influence social contagion
Eyre and team note that existing studies have already started mapping a concept called "social contagion," suggesting that our social environments impact our emotional profiles.
Some research more specifically targeted teenagers, showing that adolescents with strong friendship groups tend to have better mental health.
"Previous studies have found social support and befriending to be beneficial to mood disorders in adolescents," Eyre points out, "while recent experiments suggest that an individual's emotional state can be affected by exposure to the emotional expressions of social contacts."
And now, the research team has looked at whether or not a teenager's friendship group can influence various mood changes, and how drastic these changes can be.
"Clearly, a greater understanding of how changes in the mood of adolescents are affected by the mood of their friends would be beneficial in informing interventions tackling adolescent depression," says Eyre.
The researchers analyzed data collected by the National Longitudinal Study of Adolescent to Adult Health, which worked with U.S. adolescents in grades 7 to 12 in the 1994 to 1995 school year. The participants were followed until 2008, when individuals in the cohort had reached adulthood.
By looking at the data on the U.S. adolescents' friendship networks and mood changes, the researchers found that the prevalent moods in a circle of friends can influence the emotional state of the individual adolescent.
Eyre and colleagues noted that depressive moods are, in fact, "contagious." Symptoms of this include feelings of helplessness, tiredness, loss of interest, poor concentration, sadness, and feelings of worthlessness.
However, even though low moods and feelings of sadness could be spread among friends, they did not typically push individual adolescents over the threshold into clinically diagnosable depression.
Mathematical models showed that the more friends exhibiting low moods in an adolescent's social circle, the more likely it was for that particular teenager to experience similar symptoms.
At the same time, the study showed that a circle of friends in which most individuals are upbeat and optimistic can improve a teenager's mood and relieve their symptoms of depression.
Tackling 'spreading of negative mood'
The researchers suggest the necessity of a twofold approach for improving teenagers' low moods. As well as encouraging them to develop friendships, efforts should be made to stop negative emotions from perpetuating in adolescents' social circles.
"Understanding that these components of mood can spread socially," they write, "suggests that while the primary target of social interventions should be to increase friendship because of its benefits in reducing of the risk of depression, a secondary aim could be to reduce spreading of negative mood."
Co-study author Prof. Frances Griffiths, from the University of Warwick Medical School, explains that the research could be harnessed to improve current approaches in health policy, especially targeting subthreshold depression in adolescents.
She says, "The results found here can inform public health policy and the design of interventions against depression in adolescents."
"Subthreshold levels of depressive symptoms in adolescents is an issue of great current concern as they have been found to be very common, to cause a reduced quality of life, and to lead to greater risk of depression later on in life than having no symptoms at all," concludes Prof. Griffiths.