Are obesity and smoking contagious?

The Framingham Heart Study is perhaps the most famous long-term medical study. As every medical student learns, starting in 1948, the lifestyle habits of thousands of residents of Framingham, Masschusetts were followed to determine important risk factors for cardiovascular disease. It is because of this study that your physician can, with a few keystrokes, predict with great accuracy your risk of having a heart attack within the next 10 years and what you can do to reduce that risk. I've found the "Framingham calculator" to be a terrific educational tool in my practice, especially to illustrate the typically underestimated heart benefits of quitting smoking versus taking costly drugs for high cholesterol or high blood pressure.

In recent years, researchers have begun mining data from the Framingham study for other purposes. Last September, a New York Times magazine article described the work of Harvard physician Nicholas Christakis to test the theory that health-related behaviors, such as eating, exercise, and smoking, could be "contagious" - that is, could spread in a fashion similar to the way an infectious disease spreads. In 2007, Christakis and his collaborators published a paper in the New England Journal of Medicine that gave new meaning to the term "obesity epidemic": they found that Framingham Heart Study participants who had siblings, spouses, or friends become obese were at much greater risk of becoming obese themselves, an effect that was independent of geography. A year later, Christakis's team published another paper that showed the same phenomenon in smoking cessation. Your friends quit, your spouse quits, your brother or sister quits, and chances are good that you will follow their lead.

Doubtless most family physicians won't find these conclusions to be earth-shaking; since they care for all members of a family and are often tightly connected to the community in which they practice, FPs may have long suspected that the one of the keys to motivating patients to lose weight and stop smoking is to convince their family and friends to do the same. The same goes for a recent story in USA Today about pediatricians (who are only trained to care for patients age 18 and younger) belatedly recognizing the profound influence that parental health has on the health of infants and children. Reporter Liz Szabo wrote:

A growing number of pediatricians are now calling on their colleagues to address parental medical needs — such as depression, smoking cessation and vaccinations — that directly affect a baby's health.

I'm glad to hear that pediatricians have started to figure this out, but to family physicians, the benefits of treating parents and caregivers should be second nature, rather than front-page news. Unhealthy behaviors may be contagious, but so are healthy ones. Spread the word!