Air Pollution May Lower Levels of ‘Good’ Cholesterol, Increase Risk of Heart Disease

People living near heavily trafficked roadways may be at higher risk of heart disease due to fine particles in the air that lower levels of high-density lipoprotein (HDL), also known as “good” cholesterol, according to a new study from the University of Washington School of Public Health.

“Having ‘good’ cholesterol levels usually means having lower levels of low-density lipoprotein (LDL) cholesterol and higher levels of HDL cholesterol,” said Griffith Bell, lead author of the study who conducted the research as a doctoral student in the School’s Department of Epidemiology. “HDL particles have a number of beneficial properties, one of the most important of which is helping to remove cholesterol from peripheral tissues, where it can cause problems.”

HDL also has anti-inflammatory and anti-oxidant properties, which can help maintain good cardiovascular health, Bell added.

The study, published online April 13 in Arteriosclerosis, Thrombosis and Vascular Biology (a journal of the American Heart Association), examined the relationship between air pollution and both HDL cholesterol and HDL particle numbers. Researchers studied 6,654 adults and found that people who live in areas with high levels of traffic-related air pollution tended to have lower HDL levels.

“These findings strengthen the biological evidence linking traffic-related air pollution with cardiovascular disease,” Bell said. “Researchers have known for some time that being exposed to higher levels of traffic-related air pollution was associated with greater risk of cardiovascular disease, but only recently are scientists beginning to understand how that might work.”

Bell and the research team focused on fine particle matter smaller than 2.5 micrometers in diameter, called PM 2.5. Particle matter is a mixture of solids and liquid droplets than can include dust, dirt, soot and smoke. Researchers also looked at black carbon, a marker of traffic exhaust.

Researchers used participants’ home addresses to estimate average exposure to PM 2.5 and black carbon over 12-month, three-month and two-week periods in the year 2000.

Over one year, adults exposed to more black carbon had lower levels of HDL cholesterol than those with little or no exposure to black carbon. The difference was small, but statistically meaningful.

Study participants were ages 45 to 84 years and from diverse ethnic backgrounds, and half of them were current or former smokers. About 16 percent of the participants took cholesterol-lowering drugs and roughly 45 percent had high blood pressure. None had heart disease at the start of the study.

These findings are part of the Multi-Ethnic Study of Atherosclerosis, an ongoing study in the United States examining the lifestyle factors that predict development of cardiovascular disease. Senior authors include Samia Mora, Philip Greenland, Michael Tsai, Edward Gill and Joel Kaufman.