March 13, 2009 -- Whether you drive, take the bus, or bicycle, being in heavy traffic triples your risk of heart attack within one hour.
Air pollution from car fumes is the likely culprit, suggest Annette Peters, PhD, and colleagues at the Institute of Epidemiology, Helmholtz Center, Munich, Germany.
In a previous study, Peters and colleagues found that a sizeable proportion of heart attacks -- about 8% -- could be attributed to being in traffic.
To follow up, the researchers interviewed 1,454 people who survived heart attacks. In the hour before their heart attack, many of the survivors had been in heavy traffic.
Analysis of the data showed that these heart-attack-vulnerable people were 3.2 times more likely to suffer a heart attack if they'd been in heavy traffic in the previous hour.
"One potential factor could be the exhaust and air pollution coming from other cars," Peters says in a news release. "But we can't exclude the synergy between stress and air pollution that could tip the balance."
Making it less likely that stress was involved was the fact that patients didn't have to be driving; the risk was the same whether they were driving or taking the bus.
Traffic appeared to be five times more dangerous to women than to men in the study, although the relatively small number of women in the study (325) may have made this calculation less accurate.
To nail down the true culprit, Peters and colleagues are working with University of Rochester researchers to determine exactly what it is about traffic that raises heart attack risk.
In that study, 120 healthy volunteers are driving to work and running errands wearing heart monitors, while other instruments measure their exposure to air pollution and to noise. The data and findings from this trial are not yet available.
Peters reported the current findings at this week's American Heart Association (AHA) meeting in Palm Harbor, Fla.