People with heart disease may want to steer clear of heavy traffic when exercising or simply take their workout indoors to avoid breathing polluted air.
Exercising in areas with high levels of diesel exhaust and microscopic soot particles is especially risky for people with heart disease, according to the first study in which heart patients were directly exposed to pollution.
European researchers found that brief exposure to diluted diesel exhaust during exercise reduced a key anti-clotting substance in the blood and worsened exercise-induced ischemia, or insufficient flow of blood and oxygen to the heart -- changes that can trigger a heart attack and even death.
"We now have evidence that being exposed to diesel fuel during exercise will cause cardiac ischemia, and that if you have heart disease, it can only make things worse," said Dr. Abraham Sanders, a lung specialist at New York-Presbyterian Hospital who was not involved in the study.
The results have big implications: About 16 million Americans have heart disease, according to the American Heart Association.
In addition, people with asthma, bronchitis and chronic obstructive pulmonary disease also should use caution and avoid polluted air when exercising, Sanders recommended.
Numerous studies have shown a link between short-term and long-term exposure to air pollution and higher rates of hospitalizations and deaths due to poor blood supply to the heart, abnormal heart rhythms, gradual heart failure and stroke.
This study adds to that knowledge about how air pollution harms people and aims to show what pollution is doing in the body, information that eventually might give clues for preventing such problems, said Dr. Howard M. Kipen, director of clinical research at Rutgers University's Environmental and Occupational Health Sciences Institute.
"It's quite amazing, what they found," but not a surprise, he said.
The European study was reported in Thursday's New England Journal of Medicine.
Researchers in Sweden and the United Kingdom tested 20 men aged about 60 who had survived a heart attack at least six months earlier.
On two separate occasions, each man was put in an enclosed chamber for an hour and exposed to either diluted diesel exhaust or clean, filtered air.
They rode an exercise bike for two 15-minute periods and rested in between.
While exercising and exposed to diesel exhaust, the men experienced drops in the heart's electrical activity two to six times greater than when they were breathing filtered air. Those reductions indicated the heart muscles were not getting enough blood.