A piece from the New York Times a year ago posed the question, "Are Your Friends Making You Fat?" The article looked at research done in Framingham, Mass., where the National Heart Institute has been tracking residents and their descendents in trying to better understand the causes of heart disease.
By logging medical information over time as well as social and family networks, the study provided evidence to social scientists that appeared to prove what until recently was accepted as common wisdom but not scientific fact: health and happiness are contagious, as are poor habits and pessimism.
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.The study seems to indicate that the people you surround yourself with shape what you think is "normal," and that this effect is strengthened by how tight of a bond you share with them. Still, the study also indicates that influences can also skip over a person and affect others three degrees away -- so even if your friend's lifestyle doesn't slide to match your weight gain, his perception of "acceptable" health has nonetheless shifted, and his brother may sense it is therefore now OK for him to inhale a bag of Cheetos for breakfast. As someone who picked up smoking, poor eating habits, and about 15 pounds during university after "temporarily" leaving martial arts practice, I can see the wisdom gained from Framingham. When I look back at how my social network shifted from happy gym rats to contentious couch potatoes after high school, I can see a direct correlation with the overall decline in my physical and mental health during my 20s.

“Even as we are being influenced by others, we can influence others,” Christakis told me when we first met. “And therefore the importance of taking actions that are beneficial to others is heightened. . . . . . For most of us, within three degrees we are connected to more than 1,000 people — all of whom we can theoretically help make healthier, fitter and happier just by our contagious example. “If someone tells you that you can influence 1,000 people,” Fowler said, “it changes your way of seeing the world."Who do you influence and in what way? (Hat-tip to Sifu Joey)