A new study presented at the American Heart Association's 49th Annual Conference on Cardiovascular Disease Epidemiology and Prevention in Florida found that people were three times more likely to have an attack if they had recently spent time on the roads, possibly because of the exhaust fumes and other pollution they inhaled.

Women were five time more likely than normal to suffer a heart attack if they had been exposed to traffic within the preceding hour, the study found.

Lead author of the study Annette Peters, PhD, and her colleagues at the Institute of Epidemiology, Helmholtz Center, Munich, Germany interviewed 1,454 people who survived heart attacks. The average age of the participants was 60 years and about 25 percent were women. In the hour before their heart attack, many of the survivors had been in heavy traffic.

The researchers found that people were 3.2 times more likely to suffer a heart attack within the first hour after traffic exposure. Moreover, even six hours after exposure, there remained a significant – though small – increase in risk.

“One potential factor could be the exhaust and air pollution coming from other cars, but we can't exclude the synergy between stress and air pollution that could tip the balance,” said Dr. Peters.

The results of the study add to previous studies showing that people participating in strenuous activity such as playing soccer or squash or performing heavy work such as painting overhead or snow shoveling had five to six times the risk of heart attack in the subsequent hours after the activity.

“Measures to improve air quality within metropolitan areas and reduction of emissions from vehicles are likely to reduce risk for heart attacks,” Dr. Peters concluded.