A wealth of studies have suggested a link between exposure to air pollution and a greater risk of cardiovascular disease. New research suggests that the effects of such pollution on levels of “good” cholesterol may be to blame.

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Researchers have found that high exposure to traffic-related air pollution might lower levels of ‘good’ cholesterol.

Published in the journal Arteriosclerosis, Thrombosis, and Vascular Biology, the new study suggests that adults who reside in areas with greater air pollution – particularly traffic-related air pollution – may have lower levels of high-density lipoprotein (HDL) cholesterol.

HDL cholesterol is often referred to as “good” cholesterol. This is because it helps to remove low-density lipoprotein (LDL) cholesterol, or “bad” cholesterol, from the arteries.

Accumulation of LDL can lead to atherosclerosis, a hardening or narrowing of the arteries that can increase the risk of heart attack and stroke.

For the new study, lead author Griffith Bell, Ph.D., of the University of Washington School of Public Health in Seattle, and colleagues analyzed the data of 6,654 middle-aged and older adults taking part in the Multi-Ethnic Study of Atherosclerosis.

The air pollution exposure of each participant was estimated using information from cohort-focused monitoring campaigns, which disclosed the city in which each subject lived, when they lived there, and the air pollution levels in each city at that time.

The researchers also assessed the overall levels of HDL cholesterol in each participant, as well as the number of HDL particles. Recent studies have suggested that the HDL particle number may be a more accurate indicator of how HDL benefits the heart, compared with the cholesterol content of HDL particles.

Bell and team found that individuals with higher exposure to particulate matter (PM) – the mixture of solid and liquid particles found in the air – over an average of 3 months had a lower HDL particle number, compared with those with lower PM exposure.

Over a 1-year period, individuals with higher exposure to black carbon – a component of PM that is primarily emitted from motor vehicles – had significantly lower levels of HDL cholesterol, compared with those who had lower black carbon exposure.

Although both men and women experienced reductions in HDL cholesterol as a result of higher exposure to air pollution, the effect was stronger for women, the team notes.

According to Bell, the lower HDL levels associated with greater air pollution exposure may increase the later risk of cardiovascular disease.

While further research is needed to gain a better understanding of how air pollution affects heart health, the researchers believe that their study has provided some insight.

“[…] our study helps strengthen the biological plausibility of the link between traffic-related air pollution and cardiovascular disease. We’re slowly beginning to understand some of the biology of how that link works.”

Griffith Bell, Ph.D.

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