According to a new study, if a person's spouse quits smoking he/she is 67% less likely to smoke, and friends of a person who quits are 36% less likely to smoke, while siblings are 25% less likely. Even though smoking is addictive, giving up seems to be catching.

You can read about this new study in the New England Journal of Medicine (NEJM).

In this study researchers, Dr Nicholas Christakis from Harvard Medical School and James Fowler from the University of California in San Diego, assessed people's smoking habits and studied what effect giving up had on the probability of wives, siblings, friends, and work colleagues continuing to smoke. The study appears to show that quitting does have a major impact on other people's smoking habits, what the researchers call "the collective dynamic of smoking behavior".

The study was funded by the NIH (National Institutes of Health), the Robert Wood Johnson Foundation, and the National Heart Lung and Blood Institute. It was a secondary analysis of information from a prospective cohort study. The information came from the Framingham Heat Study, a long-running study involving 12,067 individuals which has been tracking people and their social networks in Framingham, USA, for several decades.

When the Framingham Heat Study started in 1948 there were 5,209 participants. 5,124 people were added to the study in 1971 - the additions consisted of the original group's children and spouses. A further 508 were added in 1994, plus 4,095 offspring in 2002.

The present study focused on 5,124 people, consisting mainly of the children of the previous groups. The researchers were able to find 53,000 family ties with other people in the network - approximately 10.4 family ties per person.

Clusters of smokers and non-smokers

The researchers explained that "clusters" of smokers and non-smokers appear to develop - smokers are more likely to be linked to other smokers, while non-smokers do so with other non-smokers. This clustering extends to three degrees of separation. Even though the percentage of smokers dropped, smoking clusters remained pretty constant throughout the whole period of the study - this suggest that whole groups of people were quitting at the same time.

If a husband quits it appears that the likelihood of the wife smoking drops by 67% (and vice-versa, if the wife quits..). If a person quits the chances of his/her sibling being a smoker drops by 25%. The researchers also found that if person gives up there is an impact on his/her work colleagues (their chances of smoking drop). This impact was found to be greater the more educated a person and his/her social network is.

The researchers believe that the knock-on effect of people giving up smoking has been a major factor in the smoking decline over recent decades. Smoking behavior really does influence smoking habits of others. "Groups of interconnected people stop smoking in concert", the researchers explain.

"The Collective Dynamics of Smoking in a Large Social Network"
Nicholas A. Christakis, M.D., Ph.D., M.P.H., and James H. Fowler, Ph.D
NEJM - Volume 358:2249-2258 - May 22, 2008 - Number 21
Click here to view abstract online



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