Lead author Robert B. Devlin of the U.S. Environmental Protection Agency's National Health and Environmental Effects Research Laboratory in Research Triangle Park, N.C., said the study involved 23 healthy volunteers, ages 19-33, exposed to 0.3 parts per million of ozone -- higher than the federal government's 8-hour ozone standard of 0.076 ppm.
Study participants underwent two controlled exposures -- one to clean air and one to ozone-polluted air -- at least two weeks apart. During each exposure, participants alternated 15-minute periods of stationary cycling and rest.
None of the participants reported complaints or physical symptoms after inhaling clean air or ozone, but immediately following and the morning after ozone inhalation, tests showed significant ozone-induced vascular changes compared to clear-air exposure.
The study, published in the journal Circulation, found an increase in blood levels of interleukin 1beta, a signature marker of inflammation that appears to play a key role in heart disease; a decrease in plasminogen activator inhibitor 1 and plasminogen, components that play an important role in dissolving blood clots that may form along arterial walls; and a change in heart rhythm, indicating altered autonomic nervous system control of heart rate.
"This study provides a plausible explanation for the link between acute ozone -- air pollution and sunlight -- exposure and death," Devlin said in a statement.
An estimated 40,000-50,000 U.S. deaths occur each year because of acute exposure to air pollution.