Smoking and the decision to quit spreads through social ties, both close and distant, said researchers in the US, who looked into smoking patterns in social networks and found that people follow the quitting habits of their spouses, friends, brothers and sisters, and in small firms, behaviour of work colleagues was also influential.

The study was the work of researchers Dr Nicholas A Christakis, of Harvard Medical School, in Boston, Massachusetts, and Dr James Fowler, of the University of California, San Diego, and appears in the May 22, 2008 issue of the New England Journal of Medicine, NEJM. It was was funded primarily by the National Institutes of Health’s National Institute on Aging (NIA), and was also supported by the Robert Wood Johnson Foundation.

In their background information, Christakis and Fowler wrote there has been a substantial fall in the number of smokers in the US in the last 30 years and they wanted to find out how social ties affected smoking behaviour and the decision to quit in particular.

The two researchers studied a rich set of data from over 12,000 people who were part of a densely interconnected social network and had been assessed several times between 1971 and 2003 as participants of the Framingham Heart Study. The participants ranged from 21 to 70 years of age and a person was classed as a smoker if they smoked one or more cigarettes a day.

Christakis and Fowler used network analytics and longitudinal statistics to examine how smoking and quitting behaviours spread in the different social ties of the network.

The results showed:

  • The presence of distinct clusters of smokers and nonsmokers in the network, extending to three degrees of separation (person A knows person B who knows person C who knows person D, but they don’t necessarily all know each other).
  • Although the number of smokers went down in the overall population over the 30 or so years of data, the size of clusters of smokers stayed constant, suggesting that quitting was a group behaviour that people did together.
  • Smokers were found to be increasingly marginalized to the periphery of the social network.
  • A person was 67 per cent less likely to be a smoker once their spouse had quit, 25 per cent less likely once their sibling quit, 36 per cent less likely once a friend quit, and in small firms, 34 per cent less likely once a co-worker quit (there was little significant influence among co-workers in large firms).
  • Friends with more education were more likely to pass the habit to each other than those with less education.
  • There was no such effect among immediate geographic neighbours.

When Christakis and Fowler examined the dynamics of the social network, they found that smokers had initially occupied the most richly interconnected centre of the network, but over time, they had gradually drifted to the edges, where there fewer social ties among members.

They also found that smoking rates among this study group followed the national trend over the 30 or so years covered by their analysis. In 1971 there were many smokers, they mixed equally with nonsmokers and were spread throughout the network. But by the year 2000, smoking rates had dropped significantly, and smokers and nonsmokers tended to form separate clusters, with more smokers at the fringes of the network.

Another interesting phenomenon that emerged when Christakis and Fowler looked more closely at the social patterns, was the effect of higher educational levels. Among friends where both had spent at least one year at college, a decision to quit on the part of one decreased the chance of the other smoking by 61 per cent, but no such influence was found among friends who finished their education at high school or earlier.

Also, more highly educated smokers appeared to become more marginalized, since they became less central to the network than their less educated counterparts.

The authors concluded that network phenomena appear to play a part when people give up smoking and that:

“Smoking behavior spreads through close and distant social ties, groups of interconnected people stop smoking in concert, and smokers are increasingly marginalized socially.”

Christakis said that it was interesting how it was not geographic but social proximity that influenced smoking and quitting habits.

He and Fowler said these findings should help design better clinical and public health programmes to help people quit or reduce smoking.

NIA Director Dr Richard J Hodes said:

“While smoking has declined significantly over the past 30 years in America, it remains a leading cause of preventable death.”

“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.”

Dr Richard Suzman, director of the NIA’s Division of Behavioral and Social Research said the study had an important public health message and that it suggests a need for:

“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.”

The Framingham Heart Study is a community-based study that has been going for 60 years and is sponsored by the NIH’s National Heart, Lung and Blood Institute (NHLBI). It has collected comprehensive measures of cardiovascular health and risk factors among three generations of participants who are linked as family, friends and co-workers.

“The Collective Dynamics of Smoking in a Large Social Network.”
Christakis, Nicholas A., Fowler, James H.
N Engl J Med 2008 358: 2249-2258.
Volume 358:2249-2258, May 22, 2008, Number 21

Click here for Abstract.

Sources: journal abstract, NIH/National Institute on Aging press statement.

Written by: Catharine Paddock, PhD