Associated Press
July 25, 2007 - 08:10:20 PM PST
If your friends and family get fat, chances are you
will too, researchers report in a startling new study that suggests
obesity is "socially contagious" and can spread easily from person to
person.
The large, federally funded study found that to be
true even if your loved ones lived far away. Social ties seemed to play
a surprisingly strong role, even more than genes are known to do.
"We were stunned to find that friends who are
hundreds of miles away have just as much impact on a person's weight
status as friends who are right next door," said co-author James Fowler
of the University of California, San Diego.
The study found a person's chances of becoming obese
went up 57 percent if a friend did, 40 percent if a sibling did and 37
percent if a spouse did. In the closest friendships, the risk almost
tripled.
Researchers think it's more than just people with
similar eating and exercise habits hanging out together. Instead, it may
be that having relatives and friends who become obese changes one's idea
of what is an acceptable weight.
Despite their findings, the researchers said people
should not sever their relationships.
"There is a ton of research that suggest that having
more friends makes you healthier," Fowler said. "So the last thing that
you want to do is get rid of any of your friends."
The study was published in Thursday's New England
Journal of Medicine and funded by the National Institute on Aging.
Researchers analyzed medical records of people in the
Framingham Heart Study, which has been following the health of residents
of that Boston suburb for more than a half century. They tracked records
for relatives and friends using contact information that participants
provided each time they were examined over a 32-year period.
In all, 12,067 people — all Framingham participants —
were involved in the study.
After taking into account natural weight gain and
other factors, researchers found the greatest influence occurred among
friends and not in people sharing the same genes or living in the same
household. Geography and smoking cessation had no effect on obesity
risk.
On average, the researchers calculated, when an obese
person gained 17 pounds, the corresponding friend put on an extra 5
pounds.
Gender also had a strong influence. In same-sex
friendships, a person's obesity risk increased by 71 percent if a friend
gained weight. Between brothers, the risk was up by 44 percent and 67
percent between sisters.
Indiana University statistician Stan Wasserman said
while the study was clever, it had its limitations because it excluded
relationships outside of the Framingham group.
Obesity is a global public health problem. About 1.5
billion adults worldwide are overweight, including more than 400 million
who are obese. Two-thirds of Americans are either overweight or obese.
Much of the recent research focus has been on the
intense hunt for obesity genes involved in appetite or calorie burning.
Treatment has been mainly centered on helping individuals curb their
weight through better diet and fitness.
The findings could open a new avenue for treating
this worldwide epidemic. The researchers said it might be helpful to
treat obese people in groups instead of just the individual.
"Because people are interconnected, their health is
interconnected," said lead author Dr. Nicholas Christakis, a Harvard
sociologist.
Obesity experts not involved in the research said the
results back up what they have suspected all along — that people look
toward one another for what is an acceptable weight.
"If you're just a little bit heavy and everyone
around you is quite heavier, you will feel good when you look in a
mirror," said Dr. David Katz, director of Yale University's Prevention
Research Center.
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On the Net:
New England Journal:
http://www.nejm.org
Harvard University:
http://www.harvard.edu
Framingham Heart Study:
http://www.framinghamheartstudy.org
University of California, San Diego:
http://www.ucsd.edu
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