Youths who lived in towns with strict bans were 40 percent less likely to become regular smokers than those in communities with no bans or weak ones, the researchers reported in the May issue of the Archives of Pediatrics & Adolescent Medicine.
The findings back up the idea that smoking bans discourage tobacco use in teens by sending the message that smoking is frowned upon in the community, as well as simply by reducing their exposure to smokers in public places, said Dr. Michael Siegel, of Boston University School of Public Health, and the study's lead author.
"When kids grow up in an environment where they don't see smoking, they are going to think it's not socially acceptable," he said. "If they perceive a lot of other people are smoking, they think it's the norm."
Siegel and his colleagues tracked 2,791 children between ages 12 and 17 who lived throughout the northeastern state of Massachusetts. There were no statewide restrictions when the study began in 2001 but about 100 cities and towns had enacted a hodgepodge of laws restricting smoking in workplaces, bars or restaurants.
The teens were followed for four years to see how many tried smoking and how many eventually became smokers.
Overall, about 9 percent became smokers - defined as smoking more than 100 cigarettes.
In towns without bans or where smoking was restricted to a designated area, that rate was nearly 10 percent. But in places with tough bans prohibiting smoking in restaurants, just under 8 percent of the teens became smokers.
The study found that having a smoker as a parent or a close friend was a factor in predicting whether children experiment with cigarettes. But strong bans had a bigger influence on whether smoking grew into a habit, reducing their chances of becoming smokers by 40 percent.
"There is really no other smoking intervention program that could cut almost in half the rate of smoking," Siegel said.
Age was also a factor. Smoking bans had a greater effect on younger teens than on older teens.
A statewide workplace smoking ban that included restaurants went into effect in mid-2004. Since then, high school smoking rates in Massachusetts have continued to decline, from about 21 percent of students in 2005 to about 18 percent in 2007.
Many restaurant owners fought the ban, saying it could drive away diners, according to Janine Harrod, director of government affairs for the Massachusetts Restaurant Association, which represents 2,000 restaurant owners.
While some restaurants were hurt initially, the effects have eased over time since the ban applies to everyone, she said.
Bill Phelps, a spokesman for Altria, parent company of cigarette-maker Philip Morris USA, said the study shows that the reasons teens take up smoking are complex.
"There is no single reason why young people engage in risky behaviors like smoking," he said. "We believe that there should be a multifaceted approach to address youth smoking."
At least 23 U.S. states, Washington, D.C., and Puerto Rico require most public places and workplaces, including restaurants and bars, to be smoke free, according to the National Conference of State Legislatures.
Another nine states ban smoking in workplaces but have various exemptions for restaurants or bars.