QUITTING IS CONTAGIOUSImages display social connections of smokers and non-smokers in 1971 (left) and 2001 (right). Yellow nodes represent smokers and green nodes represent non-smokers. Orange arrows denote friendship or marital ties and purple arrows denote family ties. In 1971, many smokers were dispersed throughout interconnected social groups. In 2001, fewer people smoked and those who did were on the fringes of social groups.J. Fowler

The Marlboro Man and Joe Camel exude a rugged individualism in cigarette advertisements that actual cigarette smokers shun, at least when they elect to kick the habit. Instead of going it alone, tobacco users who quit do so along with others whom they know and love, even if they live far apart, a new study suggests.

Decisions to quit smoking are often made by groups of people connected to each other at up to three degrees of separation, say physician and sociologist Nicholas Christakis of Harvard Medical School in Boston and political scientist James Fowler of the University of California, San Diego.

From 1971 to 2004, clusters of smokers participating in a large heart health study tended to quit all at once, Christakis and Fowler report in the May 22 New England Journal of Medicine. Quitters frequently maintained a greater number of social contacts than they had as smokers. In contrast, those who hung on to their tobacco habit became increasingly isolated from others and in many cases ended up socializing only with fellow smokers.

Christakis suspects that growing cultural opposition to cigarette use over the past few decades influenced attitudes about smoking in the networks of spouses, relatives, friends and coworkers. Quitting then spread from person to person in some groups, like one domino knocking down the next, and more often flared through entire groups, like houses of cards collapsing in a gust of wind.

“It is as if the cultural fabric changes and, like a flock of birds turning together to the right or left, whole groups of people quit smoking at once,” Christakis says.

Smoking-cessation programs that target cigarette users who share social networks may work better than efforts aimed at individuals, he suggests. The new findings also raise treatment concerns, adds physician Steven Schroeder of the University of California, San Francisco. Since smokers who haven’t quit have gravitated onto social islands with fellow tobacco users, it may be harder than ever for them to quit, Schroeder says. Die-hard smokers also struggle with the stigma of elevated rates of mental illness and substance abuse.

Overall, smoking rates in the new study mirrored national declines in smoking over the same time period. Smoking prevalence among persons aged 40 to 49, for example, dropped from 66 percent in 1971 to 22 percent in 2004. Still, cigarette smoking remains the leading cause of preventable death in the United States, with 440,000 fatalities attributable to the habit annually.

Some relationships in social networks affected quitting more than others did, the researchers say. If a sibling quit smoking, a person’s probability of continuing to smoke decreased by 25 percent. That decrease became 36 percent if a friend quit smoking and 67 percent if a spouse quit.

Coworkers wielded influence only in small firms, where smoking cessation by a colleague resulted in a 34 percent decline in a person’s chances of continuing to smoke.

Strong friendships and social contacts among college-educated persons elicited especially pronounced declines in cigarette use.

Spouse and family effects remained substantial whether people began the study as light, moderate or heavy smokers. On their own, friends mainly succeeded in altering the behavior of light smokers.

Indirect contacts, such as friends of friends and relatives of spouses, also contributed to decisions to quit smoking. Conversely, neighbors who quit smoking had no effect on participants’ cigarette use.

Christakis and Fowler reconstructed the social networks of 5,124 participants in the Framingham Heart Study. These networks consisted of 53,228 connections among family, friends and coworkers. The researchers’ analysis drew on extensive information about each volunteer collected every three to four years during the 32-year investigation.

The same sample indicated that obesity spreads through social networks (SN: 7/28/07, p. 51).

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