Exercising in Traffic Is Bad for the Heart

If your running route takes you into traffic, you might want to remap it.

A growing body of evidence suggests that air pollution may take a big toll on your heart. The latest research, published Wednesday in the New England Journal of Medicine, shows that diesel fumes—a major contributor to particulate air pollution—can restrict the amount of blood that reaches the heart and impair the body's ability to prevent clotting. This follows on the heels of research published in Circulation in July that showed people who live closer to heavy traffic tend to have higher rates of coronary atherosclerosis.

Previous research has suggested a link between busy roads and heart problems. One study of post-menopausal women, published this February, found that each increase in particulate matter of 10 micrograms per cubic meter was linked to a 76 percent rise in the risk of death from cardiovascular disease. Another major study published in 2004 showed that exposure to traffic pollution seemed to increase the chance of developing a heart attack within an hour of exposure by a factor of three. But the study published this week, though small, is especially convincing because it helps explain the mechanism at work. In a controlled experiment of men with coronary heart disease, the researchers discovered that exposure to diesel fumes during exercise led to immediate and significant reductions in the flow of blood to the heart and reduced by a third the amount of a protective protein that prevents clotting. "The heart is under more stress when breathing in polluted air," says study author Nicholas Mills, a cardiologist at the University of Edinburgh.

Doctors and fitness experts are still making sense of the information about air pollution and heart risk, but some are starting to suggest that people, especially those at highest risk, should consider finding ways to avoid the fumes. Murray Mittleman, a cardiologist at Harvard University who wrote an editorial published with the new study, suggests that people should try to exercise away from major roadways if possible—although he emphasizes that they shouldn't stop exercising if they can't. Other doctors suggest that in the future, certain drugs, such as blood thinners, may offer a measure of protection for people at high risk. Meg Jordan, the editor of American Fitness, recommends that people check with their local air-quality boards and avoid exercising near roadways around rush hour and when pollution levels are high. "Do your jogging inside when pollution levels are high," she advises.

Wearing protective masks is not likely to have much effect, says Mills. Nor is closing your car windows when you're sitting in traffic: Air-conditioning systems can't filter out all of the ultrafine particulates. Miller hopes that governments will be inspired to strengthen emission standards. "There is always a lag in legislation behind the publication of these studies," he says. "But I expect we'll start to see legislation to reduce particulate emissions from automobiles in the next 10 years."