Just as the chicken pox virus can cut a swath through a kindergarten class, so, too, it seems, can health behaviors cascade through groups of friends, neighbors, family members, and coworkers. Last summer, researchers said that obesity and overweight seem to be "socially contagious". A recent New York Times Magazine article examined the idea that violence might be transmitted "like tuberculosis and AIDS." And now, the same researchers who published the obesity study are reporting that smoking behavior, too, spreads through social networks.
The media coverage of last year's weight study led to a lot of simplistic debate about whether we should ditch our friends who have a BMI higher than 30. But an important related point is that healthy behaviors also can be transmitted through social networks. The study, for example, found that weight loss, as well as gain, was contagious. The new research on smoking, published today in the New England Journal of Medicine, found that people tend to "quit in droves," says Nicholas Christakis, a physician in the department of healthcare policy at Harvard Medical School and coauthor of the new research. It's not surprising that having a friend quit smoking cuts a person's chance of smoking—by 36 percent, as it happens. What's interesting, says Christakis, is that a person is less likely to smoke even if a friend's friend—or a friend's friend's friend!—quits, even if the original friend does not. Somehow (and it's not known exactly how), the behavioral change gets transmitted through the community. Group norms may play a part. When it comes to binge drinking, for example, the collective attitudes will influence whether a person drinks heavily, independent of his or her personal beliefs. (Think of a college campus, where a culture of heavy drinking may influence even kids who come to school with good intentions regarding alcohol.)
So, how can you harness this contagion to make a positive difference in health? We already know that it's often easier to change behavior with the support or help of others than alone. That's why groups like Weight Watchers and Alcoholics Anonymous may produce better results than trying to diet or quit drinking solo. But we haven't yet really begun to take full advantage of the concept when it comes to designing programs to help people change behaviors, says Jennifer Ahern, an epidemiologist at the University of California's Berkeley School of Public Health.
The real potential lies in taking advantage of the network effects to make better use of resources, says Christakis. Some researchers are already focusing their messages to certain groups with the hope that it will be transmitted to others. For example, Shape Up Somerville, a program designed to prevent obesity in high-risk first- through third-graders in Somerville, Mass., tackled the home front indirectly. While the program relied on everything from healthier school lunches to the creation of safer walking routes to school, "We really tried to catalyze change in the community by working through the children," says Christina Economos, director of the program and a nutrition professor at Tufts University's Friedman School of Nutrition and Policy. "They ended up being voices in their community; kids would come home and say, 'We need to eat more fruits and vegetables and we need to make our plates look like a rainbow.'" (Schools are also overhauling the fight against fat in other ways.) And the NYT Magazine article about violence describes a program in Chicago, CeaseFire, that attempts to apply the same strategy to battling violence as is used to treat infectious diseases: "Go after the most affected, and stop the infection at its source." It's an attitude that may be increasingly applied to public health problems we never thought had anything in common with the common cold.