News Release

Wednesday, May 21, 2008

Smokers Flock Together and Quit Together

Social Networks Exert Key Influences on Decision to Quit Smoking

When smokers kick the habit, odds are they are not alone in making the move. Instead, the decision to quit smoking often cascades through social networks, with entire clusters of spouses, friends, siblings and co-workers giving up the habit roughly in tandem, according to a new study supported in part by the National Institutes of Health (NIH).

Researchers analyzing changes in smoking behavior over the past three decades within a large social network found smokers quit in groups and not as isolated individuals. Those who continued to smoke also formed clusters that, over time, shifted from the center of the social network, where social connections are more numerous, to the periphery of the group. The report, appearing in the May 22, 2008, New England Journal of Medicine and funded primarily by the National Institute on Aging (NIA), part of the NIH, could play a role in developing clinical and public health interventions to reduce and prevent smoking. The smoking analysis was also supported by the Robert Wood Johnson Foundation.

Researchers Nicholas A. Christakis, M.D., Ph.D., of Harvard Medical School, and James Fowler, Ph.D., of the University of California, San Diego, based their analysis on a social network of 12,067 people participating in the Framingham Heart Study (FHS). The FHS, a community-based study sponsored for 60 years by the NIH's National Heart, Lung and Blood Institute (NHLBI), collects comprehensive measures of cardiovascular health and risk factors among three generations of participants who are connected as family, friends and co-workers. Christakis and Fowler analyzed data collected on the network’s smoking behaviors between 1971 and 2003. The group ranged in age from 21 to 70; individuals smoking one or more cigarettes a day were deemed smokers.

The researchers found that smoking rates among the FHS participants mirrored the national downward trend of the past three decades. In 1971, there were many more smokers and they tended to mix equally with nonsmokers. But by 2000, along with a drop in smoking rates, there was also a change in their social lives. Smokers and nonsmokers tended to form separate clusters, and gradually, the smokers were marginalized on the fringes of the social network.

"While smoking has declined significantly over the past 30 years in America, it remains a leading cause of preventable death," said NIA Director Richard J. Hodes, M.D. "This study tells us that social relationships have a critical impact on health behaviors and decisions, and that people are strongly influenced by those in their social sphere."

The researchers found the closer the relationship between contacts, the greater the influence when one person quit smoking. For example:

  • When a husband or wife quit, it decreased the chance of their spouse smoking by 67 percent.
  • When a sibling quit, it reduced the chance of smoking by 25 percent among their brothers and sisters.
  • A friend quitting decreased the chance of smoking by 36 percent among their friends.
  • In small firms, a co-worker quitting could decrease smoking among peers by 34 percent. In larger firms, the influence was insignificant.
  • Neighbors did not seem to be influenced by each other’s smoking habits.

"Interestingly, geography did not appear to play a role because smoking behaviors spread between contacts living miles apart and in separate households," said Christakis. "Rather, the closeness of the relationship in the network was key to the spread of smoking behaviors."

Fowler and Christakis also found specific patterns in the spread of behaviors. For example, the higher the educational levels among the contacts, the greater the influence on smoking behavior. Among friends who both had at least one year of college, a decision by one friend to quit smoking decreased the chance of the other smoking by 61 percent. However, no such influence was found in pairs of friends with a high school education or less. The more highly educated smokers also appeared to pay a greater social price for smoking, as reflected in the fact that they became less central to the network than did the less educated.

"This study has an essential public health message — that no one is an island — our health is partially determined by our social networks and those around us," said Richard Suzman, Ph.D., director of the NIA’s Division of Behavioral and Social Research. "The decision to quit smoking cascaded throughout the web, indicating that some form of collective decision-making was taking place. The results suggest new and probably more powerful approaches to changing health behaviors, such as smoking, by careful targeting of small peer groups as well as single individuals."

Christakis and Fowler have previously studied the effect of social networks on the spread of obesity. To learn more about this research, visit

The NIA leads the federal effort supporting and conducting research on aging and the medical, social and behavioral issues of older people. For more information on research and aging, go to

The NHLBI conducts and supports research related to heart, blood vessel, lung and blood diseases, and sleep disorders. To learn more about this research and related national health education campaigns, including a Chronic Obstructive Pulmonary Disease (COPD) awareness campaign, go to

About the National Institutes of Health (NIH): NIH, the nation's medical research agency, includes 27 Institutes and Centers and is a component of the U.S. Department of Health and Human Services. NIH is the primary federal agency conducting and supporting basic, clinical, and translational medical research, and is investigating the causes, treatments, and cures for both common and rare diseases. For more information about NIH and its programs, visit

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