That's the conclusion of researchers from Harvard and the University of California at San Diego, who report in the British Medical Journal online that happiness spreads among people like a salubrious disease. Dr. Nicholas Christakis and James Fowler studied nearly 5,000 people and their more than 50,000 social ties to family, friends and co-workers, and found that an individual's happiness is chiefly a collective affair, depending in large part on his or her friends' happiness — and the happiness of their friends' friends, and even the friends of their friends' friends. The merriment of one person, the researchers found, can ripple out and cause happiness in people up to three degrees away. So if you're happy, you increase the chance of joy in your close friend by 25%; a friend of that friend enjoys a 10% increased chance. And that friend's friend has a 5.6% higher chance. (See the Year in Health, from A to Z.)
"This is a very serious piece of research. It's pioneering," says Dr. Richard Suzman, director of the division of behavioral and social research at the National Institute on Aging. "We are barely beginning to understand its translational and applied aspects."
The authors analyzed data from the Framingham Heart Study, a historic study of heart disease among nearly 5,000 people begun in 1948. Because it was designed to follow participants and their offspring over several generations, the study's creators recorded detailed information about each person's closest relatives and friends, to better keep tabs on the original participants. That database served as an ideal social laboratory for Christakis and Fowler, who questioned each participant and his or her friends and family about their emotional state three times over 20 years.
The idea of mood transfer is not exactly revolutionary. It makes sense, after all, that your happiness will affect your closest friends, and that their emotional state will influence your own. (Interestingly, the same association was not found with unhappiness, despite the old adage about misery and company, and the contagion effect was weaker among family members than friends, possibly because while people take a cue from friends, they take for granted their families and spouses.) What was less expected was that the effect was sustained up to three degrees of separation away, among people who may not necessarily know one another. You may owe your good cheer to your friend's brother's girlfriend, even if you don't know her name.
That's the power of the social network, which, the authors argue, may impact our emotional state even more than our individual choices and environments. And it is not merely a result of like seeking like. The authors compared their observed network with a control network in which they randomly assigned feelings of happiness to individuals, and were able to rule out the possibility that happy people were simply clustering together by choice. Indeed, in another study in the same issue of the BMJ, researchers from Yale University and the Federal Reserve of Boston showed a similar tendency to cluster among people who, for example, are the same height, or suffer from acne, or headaches. But once the researchers adjusted for confounding factors, the network dissolved; in Christakis and Fowler's paper, the happiness link remained unbroken.
But the effect was limited by space and time. Researchers found that the risk of catching happiness increased with proximity: so a next-door neighbor enjoys a 34% increased chance of happiness by living near a happy person, but a friend who lives across town is less affected. And the best-connected social networkers — those who were at the center of their social nodes — were more likely to become happy than people on the fringes. Viral happiness was relatively short lived, however, lasting about a year.
This is the authors' third such networking study suggesting that the social group is a powerful super-organism that wields much influence over individuals' well-being. Previous analyses by Christakis and Fowler, based on the same pool of data, have shown that obesity is similarly contagious, as is the act of quitting smoking.
The researchers' hope is that a better understanding of how people pick up and pass on behaviors will help health officials create more targeted public-health messages. Antismoking campaigns aimed at teens, for example, might be more powerful if they were geared toward the most socially connected students in a high school — rather than individual smokers. "We are always looking for areas to invest in, promising new areas of research that will give us new levels of ability to help people, and without a doubt I see this as a very promising area," says Suzman.