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 anticlotting 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. But heart and respiratory patients should keep exercising regularly because it is so beneficial to overall health, doctors stress.
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 might eventually 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. Still, "most doctors aren't aware that little bits of pollution can cause heart attacks."
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, had blockages cleared and propped open with a stent, and were getting treatment to prevent a second heart attack. The researchers noted they only tested men with stable heart disease and good tolerance for exercise, and monitored each closely to ensure none suffered any health problems.
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. The men had electrodes attached to their bodies to monitor the heart's electrical activity, like what happens in a standard heart stress test.
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.
While diesel exhaust contains many harmful chemicals, the researchers said they believe that particulates in the exhaust are the main harm to the heart patients.
A 2000 study in six U.S. cities found the strongest association between risk of death in heart patients and air pollution exposure was for microscopic air particulates, such as those in diesel exhaust.
The European researchers noted particulate concentrations can regularly hit 300 micrograms per cubic meter — the level to which the study participants were exposed — in heavy traffic, workplaces such as factories and refineries and in the world's largest cities. Levels of some of the pollutants in the diesel exhaust were far above the limits recommended by the World Health Organization, they noted.
This study only included men, but Sanders said he thinks the findings probably apply to women. A recent report from the federal Women's Health Initiative found exercise in polluted environments causes a temporary reduction in blood flow to the heart muscle.
In an editorial, Dr. Murray A. Mittleman of Beth Israel Deaconess Medical Center in Boston wrote, "these findings may represent the tip of an iceberg" on how spikes in air pollution levels affect cardiovascular risk.
Kipen said his institute also studies health effects of diesel exhaust, generally on healthy people under age 45, but they use a more natural setting rather than an exposure chamber.
"We put them in a car and drive them around on the (New Jersey) turnpike at rush hour for two hours," Kipen said.