Adults who were exposed to traffic-related air pollution had lower levels of high-density lipoprotein (HDL) cholesterol that could increase their cardiovascular disease risk, according to an epidemiological study.

None of the participants had clinical cardiovascular disease at baseline.

Lead researcher Griffith Bell, PhD, MPH, from the University of Washington School of Public Health in Seattle, and colleagues published their results online in Arteriosclerosis, Thrombosis and Vascular Biology on April 13.

In 2004, the Environmental Protection Agency provided the University of Washington with a $30 million grant for the Multi-Ethnic Study of Atherosclerosis (MESA) Air Pollution Study, which evaluated the impact of air pollution on atherosclerosis.

The trial recruited more than 700 participants from the original MESA study, which the National Heart, Lung, and Blood Institute initiated in 1999. It also included other participants from New York and Southern California.

The researchers evaluated the long- and short-term concentrations of particulate matter and black carbon, both of which are air pollutants. Black carbon is a measure of traffic-related pollution.

In all, they had data on 6,654 white, black, Hispanic and Chinese men and women who were 45 to 84 years old. Of the patients, 53 percent were female, 16 percent used lipid-lowering drugs and 45 percent had hypertension. The mean HDL cholesterol level was 50.8 mg/dL and the mean HDL particle number was 34.0 μmol/L.

The researchers found a nonsignificant association between higher particulate matter concentrations and lower HDL cholesterol concentrations and a significant association between higher concentrations of black carbon and lower HDL cholesterol levels.

In addition, higher concentrations of particulate matter during a three-month period were associated with lower HDL particle number and higher annual concentrations of black carbon were associated with lower HDL cholesterol levels.

Previous studies showed that lower HDL particle numbers were associated with cardiovascular events. The researchers also noted that lower HDL cholesterol is a traditional risk factor for cardiovascular disease.

Although the researchers could not rule out measurement error in their models, they mentioned that measurement error in air pollution estimates was likely independent of HDL measurements. They also noted that air pollution was a mixture of particles and gases, so they might not have measured all pollutants. In addition, they only measured HDL particle numbers once.

“Our study helps strengthen the biological plausibility of the link between traffic-related air pollution and cardiovascular disease,” Bell said in a news release. “We’re slowly beginning to understand some of the biology of how that link works.”