When it comes to peer pressure and smoking, the conventional wisdom (and research) shows that, especially among kids and teenagers, one often follows the other. But a new study shows that when a smoker's tobacco-using friends quit, the smoker probably will as well. Researchers at Harvard Medical School and USC studied the smoking habits of 12,067 people in Framingham, Massachusetts from 1971 to 2003 and found that when one person quits smoking, his or her spouse is 67% less likely to smoke, while his or her friends are 36% less likely to light up. What's more surprising is that quitting smoking can affect people one doesn't even know: someone two degrees of separation away from the quitter has a 29% chance of stopping, and someone three degrees away has an 11% chance. This is especially good news for women; recent reports show that ladies who crush out the Camels permanently can experience major health benefits within five years, including a 47% lower risk of dying of heart disease.

Smokers who quit can also jump-start their social lives. Dr. Nicholas Christakis, one of the authors of the Framingham study, says that over time, smokers "are likely to drive friends away." However, shunning smokers into quitting isn't necessarily a positive: Dr. Steven Schroeder of UC San Francisco tells the New York Times, "a risk of the marginalization of smoking is that it further isolates the group of people with the highest rate of smoking - persons with mental illness, problems with substance abuse, or both."

Friends Quit Smoking? You Probably Will Too [AP via MSNBC]

Study Finds Big Social Factor in Quitting Smoking [NYT]

Women Who Quit Smoking Lower Heart Risks Quickly [Washington Post]