Everyday activities such as drinking alcohol or exercising strenuously can raise an individual’s risk of a heart attack, and exposure to more potent triggers such as cocaine can significantly raise risk. But a new study finds that exposure to traffic and air pollution contributes to 12 percent of heart attacks worldwide—the most of any factor. While poor air quality may raise a particular individual’s risk only moderately, the effects add up when spread across a city, according to HSPH’s Andrea Baccarelli, who wrote an editorial that accompanied the study in the online edition of The Lancet on Feb. 24.

While previous research has emphasized increased risks to individuals, this study is significant in its emphasis on risks to the broader population, he wrote. “The important message here is that while an individual’s risk from air pollution is moderate or small, each of us is exposed, making the amount of risk intolerable for the entire community,’’ Baccarelli told The Boston Globe.