The main premise of this research is that the health of humans who are linked through a social tie is interdependent. The impact of the death of one spouse on the risk of death of the other is a well-documented example. But this interpersonal health effect is probably a special case of a broader sociomedical phenomenon, whereby illness, disability, health behaviors, health care use, or death in one person are associated with similar outcomes in those to whom that person is tied. The key question is whether health effects may obtain in social relations beyond spouses—among siblings, parents, friends, coworkers, or neighbors. Operating through a diverse set of mechanisms, for example, might not a heart attack or stroke in one individual trigger clinically and socially meaningful changes in the health or health behavior of others in the individual’s social network?
    
Theory and prior social and medical research suggest not only that such effects may exist, but also that they may be of meaningful size. Although such effects are likely weaker in nonspousal relationships than in spousal ones, they are nonetheless of substantial importance, both conceptually and practically. First, nonspousal social relations are much more numerous than spousal ones. Second, a large body of research suggests that even “weak ties” may produce social benefits, and these may possibly extend to the health domain. Third, the potential existence of such network effects raises important policy questions (e.g., regarding the origin of neighborhood effects on health or regarding cost-effectiveness assessments of health care delivery: preventing a heart attack in one person may have health implications for numerous others). Finally, nonmortal interpersonal health effects are still incompletely understood, even in spousal pairs.

This work examines interpersonal health effects in the context of cardio-vascular disease, which is responsible for almost 40% of deaths in the United States, over 5 million hospitalizations each year, and over $350 billion in medical costs and lost productivity. To do so, it uses the landmark Framingham Heart Study (FHS) supplemented by existing but heretofore unused administrative data. We focus on cardiovascular disease not only because it is the leading cause of death of Americans, but also because the risk factors for cardiovascular events are particularly well described: up to 80% to 90% of such events are preceded by modifiable risk factors, and these are extremely well measured in the FHS. Our four specific aims are to:

• develop a multipurpose panel dataset containing demographic, social, behavioral, clinical, morbidity, and mortality information about a cohort of 5,124 members of the Framingham Offspring Cohort and their identified social relations, followed for 30 years;

• describe the attributes of the members of individuals’ networks and examine how such attributes affect the onset and outcome of cardiovascular disease;

• evaluate how health behaviors in a person embedded in a social network (the “ego”) depend on prior health events or behaviors in specific others in their social network (the “alters”);

• evaluate how health events in egos depend on prior health events in specific alters.

Papers published so far based on this work include:

N.A. Christakis, “Social Networks and Collateral Health Effects – Have Been Ignored in Medical Care and Clinical Trials, But Need to Be Studied,” British Medical Journal 329: 184-185 (July 2004)

N.A. Christakis and J. Fowler, “The Spread of Obesity in a Large Social Network Over 32 Years,” New England Journal of Medicine (July 2007)