“We talk about networks all the time,” remarks HCP’s Nicholas A. Christakis, MD, PhD, MPH. “Computer networks, neural networks, social networks. But what do networks mean in terms of medicine and health care?”

They mean a great deal, Christakis believes. “To the extent that health behaviors such as smoking, drinking, or unhealthy eating spread within networks in intelligible ways,” he says, “there are substantial implications for our understanding of health behavior and health policy. By not taking into account the effects of social networks, we may fail to understand an important aspect of human health, and we may miss a part of the picture of why people become ill.”

Networks and the obesity epidemic
Christakis has studied the effects of social networks on people’s health— specifically, how ill health, disability, health behavior, health care, and death in one person can influence the same phenomena in others in a person’s social network. “Medical care has too great a focus on individuals,” notes Christakis, “whereas in fact health status is powerfully influenced by relationships between people. People are interconnected, and so is their health.”

Some of Christakis’s work has focused on the health benefits of marriage and on how ill health in one spouse can have cascading effects on the other spouse. One current area of investigation is the effects of social networks on a person’s chances of becoming obese. “We wondered whether obesity really did behave like an epidemic,” says Christakis. “Obesity is a major problem in this country, contributing to population-level increases in diabetes and disability, and possibly even to a decline in life expectancy in the United States overall. Aside from the individual health consequences, dealing with the effects of obesity can wreak havoc on our health care system.”

To study the effects of networks on obesity, Christakis and his colleagues examined the wealth of data from the landmark Framingham Heart Study—“a crown jewel in epidemiology,” he calls it—to understand the dynamics of health in longitudinally evolving networks. This very large social network involves 12,000 people, including family, friends, and neighbors, followed for over 30 years.

In the first study to show how obesity spreads through social networks— including analyses that involved the application of network science and mathematical models—Christakis and colleagues found that a person’s chances of becoming obese increase by 57 percent if s/he has a friend who becomes obese; by 40 percent if s/he has a sibling who becomes obese; and by 37 percent if a spouse becomes obese.

“These results reinforce the idea that obesity is not just an individual problem but also a collective one,” says Christakis, “so treating people for obesity in groups, such as group dieting or sports teams, may be more effective than treating individuals alone. Our results also suggest the need for a broadening of perspective regarding the cost-effectiveness of prevention or treatment of obesity.” Indeed, the study’s findings are relevant to understanding the determinants of obesity itself and its epidemic rise over the last 30 years.

To learn more
Christakis’s study on obesity was published in the July 26, 2007, issue of the New England Journal of Medicine. It was also heavily covered in the news media. Click on the links below for a selection of the coverage:

New York Times, Washington Post, Los Angeles Times, Wall Street Journal, USA Today, NBC News, ABC News, CBS News, NewsHour, CNN, Science, Scientific American, Newsweek, Time, NPR, Chicago Tribune. Also see a column by the Boston Globe's Ellen Goodman.

Also, view the video of Christakis discussing the study, the research methods, and the results.