Obesity can spread from person to person among friends, much like a virus, according to a research published in the New England Journal of Medicine on the July 26 issue.
The study involved a detailed analysis of a large social network of 12,067 people who had been closely followed for 32 years, from 1971 until 2003.
The investigators knew who was friends with whom, as well as who was a spouse or sibling or neighbor, and they knew how much each person weighed at various times over three decades. That let them examine what happened over the years as some individuals became obese.
Through the long-term analysis, the researchers found that people were most likely to become obese when a friend became obese. That increased a person's chances of becoming obese by 57 percent.
There was no effect when a neighbor gained or lost weight, however, and family members had less influence than friends.
Proximity did not seem to matter: the influence of the friend remained even if the friend was hundreds of miles away.
The same effect seemed to occur for weight loss, the investigators say.
Dr. Nicholas Christakis, a physician and professor of medical sociology at Harvard Medical School and a principal investigator in the new study, says one explanation is that friends affect each others' perception of fatness. When a close friend becomes obese, obesity may not look so bad.
The investigators say their findings can help explain why Americans have become fatter in recent years - each person who became obese was likely to drag some friends with them.
On average, the investigators said, their rough calculations show that a person who became obese gained 17 pounds (about 7.7 kg), and the newly obese person's friend gained 5 pounds (2.3 kg). But some gained less or did not gain weight at all, while others gained much more.
The research was financed by the National Institute on Aging.
Dr. Richard Suzman, who directs the office of behavioral and social research programs at the National Institute on Aging, called it "one of the most exciting studies to come out of medical sociology in decades."
The New England Journal of Medicine, a medical weekly published by the Massachusetts Medical Society, is one of the most popular and widely-read peer-reviewed general medical journals in the world.
Source: Xinhua
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