(Agencies)
Updated: 2008-05-22 15:18

A woman smokes in a bar as she drinks the Turkish traditional beverage Raki in Ankara February 12, 2008. Turkey is the eighth biggest cigarette market in the world, with nearly 60 percent of male adults estimated to smoke. Six global cigarette producers and state-run Tekel compete for the lucrative market. Picture taken February 12, 2008.[Agencies]

Nothing may feel lonelier than trying to quit smoking, but in fact, people kick the habit in clusters, U.S. researchers said on Wednesday.

The same team of experts who found that obesity may be socially contagious said they found similar patterns among smokers, with people clearly influencing others in their social and family networks.

In fact, the most isolated people are now those who remain the most addicted as their personal networks get pushed to the fringes, they wrote in the New England Journal of Medicine.

"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," said National Institute on Aging director Dr. Richard Hodes, whose institute paid for the study.

Dr. Nicholas Christakis of Harvard Medical School in Boston and Dr. James Fowler of the University of California, San Diego, studied 12,067 people who have been taking part in the Framingham study -- a study of the health and habits of nearly an entire town in Massachusetts -- for the past 32 years.

"We've found that when you analyze large social networks, entire pockets of people who might not know each other all quit smoking at once," Christakis said in a statement. "What appears to happen is that people quit in droves."

Smoking is becoming increasingly less common in the United States. In 1965, 42 percent of the population smoked, according to the U.S. Centers for Disease Control and Prevention. That number has fallen to around 20 percent.

When the Framingham study started, around 37 percent of adults smoked.

"When you look at the entire network over this 30-year period, you see that the average size of each particular cluster of smokers remains roughly the same," Fowler said in a statement. "It's just that there are fewer and fewer of these clusters as time goes on."

When the researchers looked at the patterns of who quit and when, they saw it happened almost in cascades.

Christakis gave as an example three smokers: A, B, and C. A and B are friends, and B and C are friends, but A and C do not know each other.

If C quits smoking, the chance that A will quit goes up by 30 percent, regardless of whether B also quits.

Spouses had strong effects -- when someone quit, his or her spouse was 67 percent less likely to continue smoking.

Quitters influenced their brothers or sisters -- siblings were 25 percent less likely to smoke if one of them quit, while the friend of someone who kicked the habit was 36 percent less likely to smoke.

Even co-workers are influential -- in small firms, a quitter could decrease smoking among peers by 34 percent.

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

The same team made similar findings last year for obesity, showing that people gained weight when their friends did, even if they lived in different cities.

Richard Suzman, who directs behavioral studies at the National Institute of Aging, said the research could influence policy.

"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," he said.