The air pollution finding is based on data from two clinical trials with a total of almost 800 adults in the Los Angeles area. All participants were at least 40 years old.
First, the researchers performed an ultrasound to determine narrowing of the participants' carotid arteries, the blood vessels leading to the brain. This narrowing, which decreases blood flow, is also a sign that there is narrowing in the heart arteries as well.
Next, the scientists gauged the air pollution level in the zip codes where the participants lived, paying particular attention to particles called PM2.5, which are by-products of burning fossil fuels from driving cars and smelting or processing metals.
Participants living in the areas with the highest levels of PM2.5 had the most narrowing of their carotid arteries. For every 10-point increase in PM2.5, carotid arteries were 4% narrower.
Air pollution's effect on carotid arteries was even greater in participants over 60, women, and people taking cholesterol-lowering medication. The strongest association occurred in women over 60. For every 10-point increase in PM2.5, the women's arteries were more than 15% narrower.
When exposed to air pollution, the body produces unstable molecules called free radicals, which inflame the respiratory tract and blood vessels and can cause artery damage over time, says Nino Kuenzli, MD, PhD, in a news release. He and his colleagues reported their findings at the American Heart Association's Scientific Sessions 2004.
"The public health implications could be immense" if the link between air pollution and heart disease and stroke is confirmed, write the researchers, since cardiovascular disease is a leading cause of death and many people are exposed to PM2.5 at the levels seen in the study.