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Senior Citizen Health & Medicine
Your Friends are Making You Fat, Concludes New
Research
Decline in senior citizen disability threatened
by increase in obesity
 July
26, 2007 - Are your friends making you fat? Or
keeping you slender? Or, maybe you are the cause of your friends' body
weight. This could all be true according to new research that finds
obesity is "socially contagious," spreading from person to person in a
social network. The research, funded by the National Institute on Aging,
is important to senior citizens, whose decline in disability rates in
the U.S. is threatened by the rise of obesity.
The study - the first to examine this phenomenon -
finds that if one person becomes obese, those closely connected to them
have a greater chance of becoming obese themselves. Surprisingly, the
greatest effect is seen not among people sharing the same genes or the
same household but among friends.
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Health & Medicine |
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If a person you consider a friend becomes obese,
the researchers found, your own chances of becoming obese go up 57
percent.
Among mutual friends, the effect is even stronger,
with chances increasing 171 percent, according to the study by
researchers from Harvard and the University of California, San Diego.
Appearing in the July 26 issue of the New England
Journal of Medicine, the study is coauthored by Nicholas Christakis of
Harvard Medical School and James Fowler of UC San Diego.
Christakis and Fowler also looked at the influence
of siblings, spouses and neighbors. Among siblings, if one becomes
obese, the likelihood for the other to become obese increases 40
percent; among spouses, 37 percent. There was no effect among neighbors,
unless they were also friends.
Gender played an important role in how these
statistics broke down. In same-sex friendships, individuals experienced
a 71 percent increased risk if a friend of theirs became obese.
This pattern was also observed in siblings. Here,
if a man’s brother became obese, his chances of becoming obese increased
by 44 percent. Among sisters, the risk was 67 percent. Friends and
siblings of opposite genders showed no increased risk. While the
researchers note that correlations among siblings provide evidence for a
biological, and possibly even a genetic, component to obesity, patterns
seen among friends indicate that there’s more than biology at work.
Social connections seem to be key.
Moreover, as Christakis notes, “The fact that
neighbors don’t affect each other and that geographic separation doesn’t
influence the risk among siblings or friends tells us that environmental
factors are not essential here,” says Christakis.
“Most likely, the interpersonal, social network
effects we observe arise not because friends and siblings adopt each
other’s lifestyles. It’s more subtle that that. What appears to be
happening is that a person becoming obese most likely causes a change of
norms about what counts as an appropriate body size. People come to
think that it is okay to be bigger since those around them are bigger,
and this sensibility spreads.”
Over the last 25 years, the incidence of obesity
among U.S. adults has more than doubled, shooting from 15 to 32 percent.
In addition, roughly 66 percent of U.S. adults are considered
overweight.
Public health officials have been working hard to
account for the dramatic rise in U.S. obesity rates. Many obvious
factors, such as poor diet and a sedentary lifestyle, certainly
contribute to the swelling statistics. However, these and other
explanations tend to focus exclusively on how individuals’ choices and
behaviors affect their own weight.
"But is obesity a private matter?" asked the
researchers.
The study analyzed data over a period of 32 years
for 12,067 adults, who underwent repeated medical assessments as part of
the Framingham Heart Study.
Christakis and Fowler derived information from
archived, handwritten administrative tracking sheets dating back to
1971. All family changes for each study participant, such as birth,
marriage, death, and divorce, were recorded.
In addition, participants had also listed contact
information for their closest friends. Coincidentally, many of these
friends were also study participants.
They were able to map a densely interconnected
social network of the study's subjects by using the tracking sheets
(which had previously been archived in a basement) that recorded not
only the subjects' family members but also unrelated friends who could
be expected to find them in a few years.
The network map took two years to assemble and
includes information on the participants' body-mass index. Among the
first things the researchers noticed was that, consistent with other
studies finding an obesity epidemic in the U.S., the whole network grew
heavier over time.
Also immediately apparent were distinct clusters of
thin and heavy individuals. Statistical analysis revealed that this
clustering could not be attributed solely to the selective formation of
ties among people of comparable weights.
"It's not that obese or non-obese people simply
find other similar people to hang out with," said Christakis, a
physician and a professor in Harvard Medical School's department of
health care policy. "Rather, there is a direct, causal relationship."
Further analysis also suggested that people's
influence on each other's obesity status could not be put down just to
similarities in lifestyle and environment, to, for example, people
eating the same foods together or engaging in the same physical
activities.
Not only do siblings and spouses have less
influence than friends, but also geography doesn't play a role. The
striking impact of friends seems to be independent of whether or not the
friends live in the same region.
"When we looked at the effect of distance, we found
that your friend who's 500 miles away has just as much impact on your
obesity as [one] next door," said Fowler, an associate professor of
political science at UC San Diego and an expert in social networks.
In part because the study also identifies a larger
effect among people of the same sex, the researchers believe that people
affect not only each other's behaviors but also, more subtly, norms.
"What appears to be happening is that a person
becoming obese most likely causes a change of norms about what counts as
an appropriate body size. People come to think that it is okay to be
bigger since those around them are bigger, and this sensibility
spreads," said Christakis.
"This is about people's ideas about their bodies
and their health," Fowler said. "Consciously or unconsciously, people
look to others when they are deciding how much to eat, how much to
exercise and how much weight is too much."
"Social effects, I think, are much stronger than
people before realized. There's been an intensive effort to find genes
that are responsible for obesity and physical processes that are
responsible for obesity and what our paper suggests is that you really
should spend time looking at the social side of life as well," said
Fowler.
The policy implications of the study, the
researchers say, are profound. The social-network effects extend three
degrees of separation -- to your friends' friends' friends -- so any
public-health intervention aimed at reducing obesity should consider
this in its cost-benefit analysis.
"When we help one person lose weight, we're not
just helping one person, we're helping many," Fowler said. "And that
needs to be taken into account by policy analysts and also by
politicians who are trying to decide what the best measures are for
making society healthier."
"It's important to remember," Fowler said, "that
we've not only shown that obesity is contagious but that thinness is
contagious."
“The rising rate of obesity threatens to reverse
the decline in disability in the older population, with major
implications for the health care system,” says Richard Suzman, Ph.D.,
director of the NIA’s Behavioral and Social Research Program.
“This seminal study breaks important new ground in
showing how social networks may amplify other factors and help account
for the dramatic increase in obesity across the population.”
This research was funded by the National Institute
on Aging of U.S. National Institutes of Health.
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