Study
Links Social Networks of Family and Friends to Obesity
People wondering about excessive weight gain might look
to their relationships with family and friends for one clue, says new research
reported in the New England Journal of Medicine.
The study shows that obesity spreads within social networks
and that the closer the social connection - even if people live in different
households many miles apart - the greater the influence on developing obesity.
The study is the first to provide a detailed picture of
the social networks involved in obesity and could prove useful in developing
both clinical and public health interventions for obesity.
Nearly one in three American adults, 66 million men and
women, are obese, which puts them at risk for a number of serious health problems,
including type 2 diabetes, heart disease, and stroke.
"With the sharply rising rates of obesity in this country,
we need to learn as much as we can about contributing factors," says National
Institute on Aging (NIA) Director Dr. Richard J. Hodes.
“This study describes social network influences that
might be an important part of that equation,” says Dr. Hodes.
A sedentary lifestyle and increased consumption of high-calorie
foods are critical factors in the steep rise in the prevalence of obesity,
the researchers note.
But they suggest that influence exists among family and
friends on developing obesity, in which the attitudes, behaviors, and acceptance
of obesity also might play an important role.
To explore whether obesity spreads from person
to person within social networks, the research team gleaned weight, height,
and other
data from the records of 5,124 Framingham Heart
Study participants at up to seven time points between 1971 and
2003.
In addition, they analyzed similar information from the
Framingham records of the parents, spouses, siblings, children, and close friends
of the key participants.
Together, these individuals formed a large, intertwined
social web totaling 12,067 people. The average age of key participants at the
inception of the study was 38 years, with a range of 21 to 70 years.
"We were able to reconstruct a large network
of individuals who had been repeatedly weighed over time as part of the Framingham
Heart Study, and we could see that as one person gained weight, those
around him or her gained weight," says Dr. Nicholas Christakis of Harvard Medical
School.
"We didn't find that people who were overweight simply flocked
together,” he says. “Rather, we found what seemed to be a spread
of obesity and that the likelihood of a person becoming obese depended on the
nature of the relationship."
Richard Suzman, Ph.D., of the NIA says, "The
rising rate of obesity threatens to reverse the decline in disability in the
older population, with major implications for the health care system."
He notes that this study breaks important new ground in
showing how social networks may amplify other factors and help account for
the dramatic increase in obesity.
Findings include:
- A key participant's chances of becoming obese increased by 57 percent if
he or she had a close friend who became obese.
- In same-sex friendships, a close friend becoming obese increased a key
participant's chance of becoming obese by 71 percent. However, no such association
was found in opposite-sex friendships.
- The perception of friendship also was an important factor. When two people
identified each other as close friends, the key participant's risk of becoming
obese increased by 171 percent if his or her friend became obese. In contrast,
a key participant was not likely to become obese if someone claimed a close
friendship with him or her but the key participant did not report the friendship.
- Among pairs of siblings, one's becoming obese increased the other's chance
of becoming obese by 40 percent. This finding was more marked among same-sex
siblings than opposite-sex siblings.
- In married couples, one spouse's becoming obese increased the likelihood
of the other spouse becoming obese by 37 percent. Husbands and wives appeared
to affect each other equally.
- Obesity spread across social ties, despite geographic distance from one
person to another.
- Further, social distance - the degree of social separation between two
people in the network - appeared to make more of a difference than geographic
distance in the spread of behaviors and norms associated with obesity.
- An immediate neighbor's becoming obese did not affect a person's risk of
becoming obese.
- Smoking behavior was not associated with the spread of obesity from person
to person.
"We identified distinct clusters of obese people within
social networks, and the clusters spread about three people deep," says Dr.
Christakis.
"People who were only one degree removed from each other
socially, such as siblings or close friends, influenced one another twice as
much as people who were two degrees removed from each other," explains Dr.
Christakis.
Always consult your physician for more information.
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