Christakis & Fowler Obesity Network

“Is Happiness Catching?” is the feature article in this week’s New York Times Magazine. Clive Thompson writes about the Framingham Heart Study, which has followed 15,000 people starting back in 1948. Originally framed as a study of physical disease, the data are now being turned to social ends.

Nicholas Christakis, a medical sociologist and doctor at Harvard, and James Fowler, a political scientist at UC San Diego, have taken this data set to examine a question that dates back to Durkheim and his ideas about collective effervescence, anomie, and suicide – how do our social relationships affect what we experience and do? As Thompson frames it:

By analyzing the Framingham data, Christakis and Fowler say, they have for the first time found some solid basis for a potentially powerful theory in epidemiology: that good behaviors — like quitting smoking or staying slender or being happy — pass from friend to friend almost as if they were contagious viruses. The Framingham participants, the data suggested, influenced one another’s health just by socializing. And the same was true of bad behaviors — clusters of friends appeared to “infect” each other with obesity, unhappiness and smoking. Staying healthy isn’t just a matter of your genes and your diet, it seems. Good health is also a product, in part, of your sheer proximity to other healthy people.

Their research shows that common explanations for problem behavior, such as individual being at fault or peer pressure, are inadequate. What we experience and how we act spreads further than we think. Take a major illness affecting a mother late in life, and the strain and stress her daughter experiences caring for her mother. That strain can affect the daughter’s husband, who in turn shapes his friend’s life.

Christakis saw this through his clinical experience, and with Fowler, decided to study the impact of social networks. One of their main findings is that in the Framinghamn study, “drinking spread socially, as did happiness and even loneliness. And in each case one’s individual influence stretched out three degrees before it faded out. They termed this the ‘three degrees of influence’ rule about human behavior: We are tied not just to those around us, but to others in a web that stretches farther than we know.”

When a Framingham resident became obese, his or her friends were 57 percent more likely to become obese, too. Even more astonishing to Christakis and Fowler was the fact that the effect didn’t stop there. In fact, it appeared to skip links. A Framingham resident was roughly 20 percent more likely to become obese if the friend of a friend became obese — even if the connecting friend didn’t put on a single pound. Indeed, a person’s risk of obesity went up about 10 percent even if a friend of a friend of a friend gained weight.

Christakis and Fowler’s work provides an in-depth description of the functioning of social networks – not a examination of why loneliness spreads so much as an examination of how it does. In other words, there is not a theory of social contagion of behaviors, but an examination of the role of social networks in loneliness. As they write in an in-press paper co-authored with John Cacioppo:

Results indicated that loneliness occurs in clusters within social networks, extends up to three degrees of separation, and is disproportionately represented at the periphery of social networks. In addition, loneliness appears to spread through a contagious process even though lonely individuals are moved closer to the edge of social networks over time. The spread of loneliness was found to be stronger than the spread of perceived social connections, stronger for friends than family members, and stronger for women than for men.

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