WEDNESDAY, Nov. 7 (HealthDay News) -- Exposure to diesel exhaust increases clot formation and blood platelet activity, boosting men's risk for heart attack and stroke, a small study has found.

The volunteers -- 20 healthy men, ages 21 to 44 -- were first exposed to clean, filtered air (as a control) and then to diluted diesel exhaust at 300 micrograms per meter cubed (mcg/m3) -- comparable to the amount breathed in by a person beside a busy street.

Tests conducted on the blood of the volunteers at two hours and six hours after exposure to diesel exhaust revealed a 19.1 percent to 24.2 percent increase in clot formation and an increase in activation of blood platelets (which play a major role in clotting) at two hours after diesel exhaust exposure.

"The study results are closely tied with previous observational and epidemiological studies showing that shortly after exposure to traffic air pollution, individuals are more likely to suffer a heart attack," study lead author Dr. Andrew Lucking, a cardiology fellow at the University of Edinburgh in the United Kingdom, said in a prepared statement.

"This study shows that when a person is exposed to relatively high levels of diesel exhaust for a short time, the blood is more likely to clot. This could lead to a blocked vessel resulting in heart attack or stroke," he said.

The study was expected to be presented Nov. 6 at the American Heart Association annual meeting, in Orlando, Fla.

Based on the findings, people with existing cardiovascular disease shouldn't exercise in areas where there's heavy traffic, Lucking added.

More information

The American Academy of Family Physicians has more about air pollution and health.