Putting down cigarettes for good can have unexpected social benefits, according to new research from Harvard and the University of California, San Diego. Smoking is bad, it turns out, not only for your physical wellbeing but for your social health, too – with smokers increasingly edged out to the margins of social circles.

Another significant finding of the study, published in the May 22 issue of the New England Journal of Medicine, is that the decision to quit appears to be taken up almost communally, with whole clusters of spouses, friends, siblings and co-workers giving up the habit at about the same time.

The researchers – Nicholas Christakis of Harvard Medical School and James Fowler of UC San Diego – analyzed changes in smoking behavior from 1971 to 2003 in a large social network of 12,067 densely interconnected people.

The study follows up on research by Fowler and Christakis published last summer, also in the New England Journal of Medicine, finding that obesity is “socially contagious” – spreading from person to person in a social network so that if one becomes obese those closely connected to them have a greater chance of becoming obese themselves.

Using data from the same Framingham Heart Study (which, among other things, was the first to identify the link between smoking and cardiovascular disease), the researchers observed that smoking behaviors are subject to similar social-network effects, at two and three degrees of separation. Except that quitting smoking, they found, spread through the network not only like one domino knocking down the next, which in turn knocks down another, but also like a house of cards collapsing.

Christakis and Fowler note that their findings speak both to the power of relationships and to the efficacy of public-health campaigns to reduce smoking. While smoking remains a leading cause of preventable death, rates in the U.S. have decreased substantially.

“When you look at the entire network over this 30-year period, you see that the average size of each particular cluster of smokers remains roughly the same,” Fowler said. “It’s just that there are fewer and fewer of these clusters as time goes on.”

Observing that “entire pockets of people who might not know each other all quit smoking at once,” said Christakis, points to a cultural shift or a change in the zeitgeist. “What appears to happen is that people quit in droves.” 

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