Friends, Family, the Framingham Heart Study and Obesity 2007

By R.C. Goode

The “person-to-person” spread of obesity is a recent observation of Nicholas Christakis and James Fowler (2007). These investigators examined the data from the Framingham Heart Study which included ~ 12,000 subjects. These subjects were studied for 32 years, from 1971 to 2003. One of the measurements taken was the Body Mass Index (BMI, the weight in kilograms divided by the square of the height in metres). Usually one is considered obese when their score is equal to or greater than 30.

Obesity is a risk factor in Heart Disease and Type II Diabetes. Some 65% of adults are overweight and ~ 30% are obese. The increase in obesity (~10%) in the last decade is considered to be an epidemic. Inactive lifestyles and eating habits have been identified as part of the problem .As Obesity affects all socio-economic groups, Christakis and Fowler described the phenomenon as akin to a “flu epidemic” and asked how might this epidemic spread.

The study investigated one individual’s weight and the weight among their family, friends and neighbors. They observed that an individual’s chances of developing obesity increased by some 57% if she/he had a friend who became obese. In families if one brother became obese, the increased risk for the other brother of becoming obese was 44% and among sisters the increased risk was 67%.Obesity in one family member did not affect the development of the condition in a family member of the opposite sex.

In married couples, if one became obese there was a 37% increase in risk that the other spouse would become obese. Among friends of the same sex, a man had a 100% increase in the probability of becoming obese if his male friend had become obese. This relationship was not established from female friend to female friend.

In addition to the association of increased risk of obesity via a social network, the authors of this study suggest that a “social network” could reverse or slow down the obesity epidemic. “People are connected and so their health is connected.” If one can modify a person’s social network (for example in a weight-loss intervention) there may be a positive result.

Christakis NA, Fowler JH. The Spread of Obesity in a Large Social Network over 32 Years. N Engl J Med 2007; 357: 370-379.

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