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Elizabeth Cooney is a health reporter for the Worcester Telegram & Gazette.
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Wednesday, July 25, 2007

Friendships may contribute to obesity epidemic

By Alice Dembner, Globe Staff

A study released today suggests that obesity spreads through social connections, particularly via close friendships.

This doesn’t replace the effects of genetics, failing to exercise or supersizing food. But researchers writing in the New England Journal of Medicine say it provides a possible explanation for the rapid increase in obesity over the last few decades. Nationally surveys show that nearly one-third of US adults are now obese.

The condition appears to spread though what researchers are calling “social contagion,” a tendency of people who become obese to influence the behavior of others and to convey -- perhaps subliminally -- the message that being overweight is okay.

"Obesity is not just an individual problem, but a collective problem," said Dr. Nicholas Christakis, a professor of medical sociology at Harvard Medical School and co-author of the report. To slow the epidemic, he said, "treating people in groups may be more effective than treating them individually."

Studying more than 12,000 people linked to a long-running study of heart disease based in Framingham, the researchers found that an individual's chances of becoming obese increased by 57 percent if someone they consider a friend grew obese.

If the friendship was close and mutual and one person became obese, the other's risk soared by 171 percent. The study found similar, but smaller influences between siblings and spouses, but neighbors who aren't friends had no effect.

Surprisingly, obesity seemed to spread even if friends were geographically distant.

"We were stunned to find that friends who are hundreds of miles away have just as much impact on a person's weight as those who are geographically close," said James Fowler, the paper's other author, who is an associate professor of political science at the University of California San Diego. This led researchers to suggest that the effect wasn't only due to sharing behaviors -- such as eating together -- but to sharing ideas about what constitutes an appropriate weight.

Because the study looked at relationships over time, the researchers were able to exclude cases in which obese people chose overweight friends, and therefore were able to make a stronger case for a causal effect.

Researchers have developed an illustration showing how relationships impact obesity.

Posted by Karen Weintraub at 01:36 PM
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