Researcher Annette Peters, Ph.D. of Harvard School of Public Health and colleagues found that sitting in traffic may be associated with an increased risk of heart attack and women had a fivefold increased risk of myocardial infarction after sitting in traffic.

Although the study did not prove causality, Dr. Peters said that the association could be explained by looking at the exhaust and air pollution caused by traffic and the "synergy between stress and air pollution that could tip the balance."

The research group found that patients who had a myocardial infarction were more than three times as likely to have been in traffic within an hour before the onset of their symptoms.

Documented previous research in one case-series of 691 patients found that exposure to traffic may trigger myocardial infarction and an association between exposure to traffic in urban areas and cardiovascular disease exacerbation.

The researchers interviewed patients about what could have triggered a heart attack. Factors considered were traffic exposure in the four days before onset of symptoms. This included driving in a car, using public transportation or riding a bicycle. Driving a car was the most common source of traffic exposure; however, bus or bike transportation were also associated with symptoms on hour later.

Other "at risk" groups included those with a history of angina and the unemployed. Dr. Peters said that it is important to find out what is behind the association between air pollution - stress or both.

The study was funded by a grant from Health Effects Institute in Boston, the Helmholtz Zentrum Munchen and the German Research Center for Environmental Health.

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