Friends’ good moods can be contagious

The flu, measles and other infectious diseases can be contagious. They can spread through social groups as people transmit germs to one another. Some people have wondered if the mental illness known as depression also spreads through social networks. It doesn’t, a new study finds.

Edward Hill was part of a research team that investigated how, if at all, teens’ moods and attitudes affect the mental health of others. “Having depressed friends does not make you more likely to become depressed yourself,” he now concludes. Hill is a graduate student at the University of Warwick in Coventry, England. There he studies complexity science, which deals with systems affected by many factors.

Depression is a disease. People who suffer from this mental illness feel ongoing sadness and apathy. Often they lack energy and have difficulty concentrating. Many have trouble working, sleeping or interacting with others. Depressed teens can be grouchy and have a prickly personality. They also face an elevated risk of suicide. Indeed, as of 2010, depression was the second leading cause of death for Americans aged 10 to 24, according to the U.S. Centers for Disease Control and Prevention. So, it’s nothing to be ignored.

While the new study showed depression was not contagious, it found good mental health can be catching. “Our study suggests that having mentally healthy friends can help someone recover from depression or even remain mentally healthy in the first place,” says Hill.

Computers did the investigation

Hill’s group used data collected from about 3,000 U.S. teens as part of a long-term survey. It followed each into early adulthood. Participants were asked at different times over the years about whether they had symptoms of depression. The teens also had a chance to name up to five male and five female friends.

The new British study took those answers and applied them to three different computer models. One model looked for any sign that the number of friends who were depressed affected a teen’s risk for depression. A second model tested for evidence that the number of friends who were not depressed affected that risk. The third was essentially a control, says Hill. It explored whether the mood of someone’s friends had nothing to do with a teen’s risk of depression.

“Basically, they were trying to go in with as few assumptions as possible,” notes Christine Klymko. She’s an expert in computational mathematics. She works at Lawrence Livermore National Laboratory in California, and had no role in the new study.

In the end, there was “no evidence” that the number of depressed friends affects a teen’s risk of developing or recovering from depression, Hill reports.

But the data did fit the model linking risk of depression to the number of friends who were not depressed. That model showed that teens with five or more mentally healthy friends were only half as likely to become depressed within 6 to 12 months as were the teens with no mentally healthy friends. And those with 10 healthy friends were about twice as likely to recover from the symptoms of depression over six to 12-months, when compared to teens with just three healthy friends.

Findings from the new study appeared August 19 in the Proceedings of the Royal Society B. 

The implications

The team’s findings differ from some earlier studies. Those earlier ones had looked at teens at just one point in time, Hill says. They couldn’t assess trends over time that might have linked mood to a particular cause. For instance, clusters of teens might have had depression and sought each other out after symptoms developed. Or heavy drinkers might hang out together. If that were true, it could explain the results because there is a link between heavy drinking and depression. Clearly, a whole host of factors can be at work, Hill notes. And they may be hard to tease out when teens are looked at just once — like a snapshot of their life.

The new study, in contrast, used data from multiple time points. By doing so, Hill explains, “We were able to observe direct changes in individuals’ mood.”

The computer models used in the new study are much like those developed from studying other diseases, notes Klymko. But using such models to probe whether mental illness spreads through social networks is “a pretty new area of research,” she adds. While many questions remain, Hill’s study is a good “start for an intervention strategy,” she says. By that she means it could be part of a planned effort to help people who are depressed — or might become so.

Depression is a serious, dangerous disease. And it “should be a public health issue, rather than an individual one,” stresses Hill. If society encourages healthy friendships among teens, this “could go some way toward providing them with a protective effect against mental-health problems.”

“There shouldn’t be a stigma” linked to depression either, Hill adds. Instead, his study shows, maintaining friendships with people who become depressed might help them feel better until they finally get better. And isn’t that what you’d want from a friend?

Power Words

(for more about Power Words, click here)

apathy A flat mood, where one is indifferent to people, opportunities and the environment around them. It’s marked by a lack of  enthusiasm for things, for not caring any more.

complexity science  The study of systems that can be influenced by a wide range of factors. Examples include the spread and management of disease, the operation of stock markets, distributed computing and other areas. The field involves both mathematical modeling and philosophical issues.

computational mathematics A branch of math that uses computer programs to describe what is known about numbers and their relationships to each other, or to predict (or calculate) the properties of other numbers.

computer model  A program that runs on a computer that creates a model, or simulation, of a real-world feature, phenomenon or event.

contagious  Likely to infect or spread to others through direct or indirect contact; infectious.

control A part of an experiment where there is no change from normal conditions. The control is essential to scientific experiments. It shows that any new effect is likely due only to the part of the test that a researcher has altered. For example, if scientists were testing different types of fertilizer in a garden, they would want one section of it to remain unfertilized, as the control. Its area would show how plants in this garden grow under normal conditions. And that give scientists something against which they can compare their experimental data.

data  Facts and statistics collected together for analysis but not necessarily organized in a way that give them meaning. For digital information (the type stored by computers), those data typically are numbers stored in a binary code, portrayed as strings of zeros and ones.

depression  A mental illness characterized by persistent sadness and apathy. Although these feelings can be triggered by events, such as the death of a loved one or the move to a new city, that isn’t typically considered an “illness” — unless the symptoms are prolonged and harm an individual’s ability to perform normal daily tasks (such as working, sleeping or interacting with others). People suffering from depression often feel they lack the energy needed to get anything done. They may have difficulty concentrating on things or showing an interest in normal events. Many times, these feelings seem to be triggered by nothing; they can appear out of nowhere.

graduate student Someone working toward an advanced degree by taking classes and performing research. This work is done after the student has already graduated from college (usually with a four-year degree).

infectious  An adjective that describes a type of germ that can be transmitted to people, animals or other living things.

intervention  A planned effort to prevent or treat a disease or other condition relating to health or well-being.

model  A simulation of a real-world event (usually using a computer) that has been developed to predict one or more likely outcomes.

nonlinear  A system where a little change in one quality can cause a big change in another.

psychology  The study of the human mind, especially in relation to actions and behavior. Scientists and mental-health professionals who work in this field are known as psychologists.

social network  Communities of people (or animals) that are interrelated owing to the way they relate to each other. In humans, this can involve sharing details of their life and interests on Twitter or Facebook, or perhaps belonging to the same sports team, religious group or school.

stigma  A disgrace, source of shame or a stain on one’s reputation — often not justifiably — due to something that one did, experienced or represents to others.