Washington, May 22 : A new study has found that when smokers quit the habit, odds are that the health triumph doesn't occur in isolation.
Instead, the decision to quit smoking is often influenced by social networks, with entire clusters of spouses, friends, siblings and co-workers giving up the habit roughly in tandem.
The study analysing changes in smoking behaviour over the past three decades within a large social network found that smokers kick the habit in groups and not as isolated individuals.
It also showed that 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 findings could play a significant role in developing clinical and public health interventions to reduce and prevent smoking.
For the study, researchers Nicholas A. Christakis, M.D., Ph.D., of Harvard Medical School, and James Fowler, Ph.D., of the University of California, San Diego, analysed a social network of 12,067 people participating in the Framingham Heart Study (FHS).
They analyzed data collected on the network's smoking behaviours 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 analysis showed that smoking rates among the participants mirrored the national downward trend of the past three decades.
The researchers found that in 1971, there were many more smokers and they tended to mix equally with non-smokers.
However, they found that by 2000, along with a drop in smoking rates, there was also a change in their social lives.
In addition, smokers and non-smokers tended to form separate clusters, and gradually, the smokers were marginalized on the fringes of the social network.
"This study tells us that social relationships have a critical impact on health behaviours and decisions, and that people are strongly influenced by those in their social sphere," NIA Director Richard J. Hodes, M.D. said.
During the study, researchers found that the closer the relationship between contacts, the greater the influence when one person quit smoking.
Fowler and Christakis also found specific patterns in the spread of behaviours. For example, the higher the educational levels among the contacts, the greater the influence on smoking behaviour.
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, researchers found no such influence 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 behaviours, such as smoking, by careful targeting of small peer groups as well as single individuals," he added.
The study is published in the May 22, 2008, New England Journal of Medicine.