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The Social Network Theory: Do Friends Affect Our Health?

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In America, the idea of individual responsibility is lauded almost as much as our freedom and personal choice. But although we are all responsible for our actions, we don’t make decisions in a vacuum. Consider how much our environment—the city we live in, our friends, the layout of our streets—dictates our personal behavior. Humans, like other animals, are part of complex social and environmental networks, meaning that our actions inherently influence the actions and reactions of those around us.

One example of this is our health. While things like diet, tobacco use, or sedentary lifestyles seem to be purely personal decisions, friends and family—our social network— can greatly influence our choices.

Obesity Is Among Us
It’s certainly no surprise that our social networks can positively and negatively influence our health. If a friend is slathering on sunscreen, you might too; when a friend decides to order another cocktail, you might too. But recent studies have managed to quantify just how this happens.

Dr. Nicholas Christakis of Harvard Medical School and James Fowler of the University of California, San Diego have done much of the work linking social networks to health. One of their first studies looked at obesity. Using data from the Framingham Heart Study, a large prospective study that follows most of the residents of Framingham, Massachusetts, they were able to look at obesity trends in a network of 12,067 people over the course of thirty years. Published in the New England Journal of Medicine, the study found that “obesity appears to spread through social ties,” suggesting that the condition, which afflicts over 30 percent of the U.S. population, moves in a manner not unlike an infectious disease.

But just how does this work? The authors speculate that having obese social contacts could increase a person’s “tolerance” for obesity (if everyone around you is big, it doesn’t seem abnormal), or might influence their adoption of certain behaviors (getting super nachos instead of a salad). Having an obese friend was found to increase a person’s risk of becoming obese by 50 percent; having an obese sibling increased the risk by 40 percent, and an obese spouse by 37 percent.

Although many factors have contributed to our obesity epidemic, including increased portion sizes and dependence on cars, social networks and the normalization of the extra pounds can contribute to an individual’s weight gain, which in turn leads to a community problem.

You Quit, I Quit, We All Quit the Habit
But social networks don’t just negatively affect health. One of the most striking examples of this is tobacco cessation. Though quitting is often portrayed as an individual’s responsibility, another study by Drs. Christakis and Fowler found that smokers tend to quit in groups. Following smokers and nonsmokers from 1971 to 2003, the researchers found that as effective tobacco use became less popular, smokers became more isolated, forming clusters among themselves. As time went on, entire groups would quit together

The smokers that remained had fewer friends and social connections; smoking had become unpopular and took the followers with it.

The study found that some social connections were more influential to quitting. If a spouse quit, it was a more influential predictor of quitting than if a friend quit; a friend quitting was more influential than a sibling quitting.

Although it comes down to a personal decision, a positive social environment can have a profound effect on what decisions we decide to make. 

So Happy Together
While it may seem logical that friends affect certain health behaviors, social network theory has also highlighted the ability of contacts to increase our happiness.

A 2008 study published in the British Medical Journal found that surrounding yourself with happy people could influence your own happiness and that body language and proximity play key roles. For instance, a next-door neighbor’s happiness increased one’s chance of happiness by 34 percent, but a neighbor living farther away had no effect. Personal circumstance had a large effect on one’s happiness, but seeing a smiling face of a friend or neighbor could also spread the joy.

The idea behind social connectedness and well-being is nothing new. Numerous social epidemiology studies have also found that, particularly for elderly populations, cognitive decline slows when people have many contacts and participate in social gatherings.

Perhaps one of the biggest influences on our personal health can be a partner’s health. For instance, one study looked at how a spouse’s illness or death can affect their partner’s death risk. A spouse’s death increased their partner’s chance of premature death by 20 percent.

Healthy Environment Begets Healthy Networks
Of course, many of the reasons for our collective behavior have to do with our shared environment, not just who we hang out with. For instance, smokers wouldn’t be quitting without effective tobacco policies, like secondhand smoke bans, increased tobacco taxes, and marketing bans, all of which contributed to an environment that made it easier for people to quit. Likewise, common events and exposures may contribute to a community’s level of happiness or sadness, and weight gain or weight loss.

But what is clear is that we can and do influence collective behavior. Social connectedness influences health, and the networks in which we are a part can spread positive and negative behaviors. So next time you’re with friends and family, think about spreading the good behaviors, not the bad.


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