By Howard LeWine, M.D.
Obesity is contagious. It spreads from person to person, but not in the same way as germs or viruses. You donâ€™t need to be standing near someone who is overweight to catch it. Obesity spreads to people who are socially connected to you, even if they live far away.
In the July 26 issue of the New England Journal of Medicine, two Harvard professors, Drs. Nicholas Christakis and James Fowler, published the results of a study that evaluated the impact of social networks on obesity. This study has caused quite a buzz. Perhaps the social connections we have with family and friends have as much influence on our body weight as genetics and individual behaviors.
The researchers looked at a vast social and familial network using data from the long-term Framingham (Massachusetts) Heart Study. Drs. Christakis and Fowler identified 12,067 Framingham people who had one or more social tie to at least one other person. Each of the individuals had periodic health evaluations between 1971 and 2003.
In addition to body measurements, each of the subjects provided other information that made the study possible. The Framingham people also filled out tracking sheets with the names and sex of siblings, spouses, neighbors, and friends, and information on the types of friendships. The researchers also collected data on smoking habits and the geographic distances between the home of each individual and his or her identified social and familial contacts.
Here are some highlights of what the researchers discovered:
- The risk of becoming obese was 37% higher when a personâ€™s spouse gained too much weight.
- For people with obese brothers and sisters, obesity was 40% more likely.
- The chance that an individual would become obese rose by 57% if a close friend became obese.
- If the friend or sibling was the same sex, the obesity link was even stronger.
So, is this just saying that heavier people naturally gravitate toward each other, or as the say saying goes -- birds of a feather flock together? The study was not designed to determine which specific mechanisms within social networks influence weight gain, but there were some powerful clues. In the article, the authors suggest that â€œthe psychosocial mechanisms of the spread of obesity may rely less on behavioral imitation (and local environment) than on a change in a personâ€™s general perception of the social norms regarding the acceptability of obesity.â€
Their findings reasonably support this suggestion. While weight gain in spouses, siblings, and friends had a large impact, weight gain in immediate neighbors did not. Also, it didnâ€™t matter how close or far away friends and siblings lived. And siblings and friends of the same sex who became obese correlated with the highest risk of the connected person also becoming obese.
In addition, how friendships were defined by individuals mattered. In a friendship that was identified as bidirectional (each named the other as a close friend), when one gained weight, it was very likely that the friend would as well. But things change if you count someone as a close friend, but that person doesn't consider you in the same way. According to this study, you would be more likely to gain weight after that person becomes obese. However, he or she would not be more likely to gain weight if you gain weight first.
This study does not mean you should alter your connections with family and friends based on body weight. Social connectedness is too important for good health. Â For example, older people who are socially engaged tend to hold on to their cognitive abilities longer. Â
How can we use the results of this study in a positive way?
Have we become too accepting of higher body weights, using the unhealthy weight gain of our friends and families to justify weight gain in ourselves?
Do you think we can use social contagion to our advantage to help us keep body weights down, without becoming obsessed?
I look forward to your thoughts, ideas and reactions.
Howard LeWine, M.D., is a hospitalist at Brigham and Womenâ€™s Hospital in Boston, where he practices and teaches Internal Medicine. He is the Chief Medical Editor of Internet Publishing at Harvard Health Publications.
You can find the following related articles on Gather: