HDL Reductions by Air Pollution May Help Explain Its CV Risks

Marcia Frellick

April 27, 2017

SEATTLE, WA — Adults who live in areas especially beset by air pollution, particularly from automobile traffic, tend to have lower HDL-cholesterol levels and lower HDL particle numbers, conclude researchers based on a study that may help explain why such pollution increases cardiovascular risk[1].

Many studies have associated air pollution with increased risk of a number of diseases, especially cardiovascular disease; the possible nature of the association has been widely explored but the answer remains elusive.

According to the work of Dr Griffith Bell (University of Washington School of Public Health, Seattle) and colleagues, published April 13, 2017 in Arteriosclerosis, Thrombosis, and Vascular Biology, the link may be related pollution's HDL-lowering effect, although by what mechanism isn't clear.

The group looked at data from 6654 white, black, Chinese, and Hispanic adults ages 45 to 84 years living in six metropolitan US regions without clinical cardiovascular disease at baseline, in the Multi-Ethnic Study of Atherosclerosis Air Pollution (MESA Air).

They studied where participants lived at the time, pollution factors at their locations, individual HDL-cholesterol levels at baseline, and number of HDL particles—which some studies have said is a better predictor of cardiovascular disease than cholesterol levels alone.

In this cohort, the mean HDL-cholesterol level was 50.8 mg/dL and the mean HDL particle number was 34 μmol/L.

The group also measured black carbon concentrations (a marker of traffic exhaust) and fine particulate matter, in this case PM2.5, which is solid and liquid matter smaller than 2.5 μm in diameter. Exposure was averaged at 2 weeks, 3 months, and 12 months before examination.

The researchers found that changes in HDL levels were seen after short and medium-length exposures to pollution. Over a 1-year period, those who had higher exposure to black carbon (0.7×10-6-m-1 higher exposure) had small but significantly lower HDL levels than did those with less exposure (-1.68 mg/dL; 95% CI -2.86 to -0.50).

Researchers adjusted for factors including HDL particle numbers, pack-years smoked, income, and niacin use.

In the 3-month exposure period, a 5 μg/m3-higher PM2.5 was associated with lower HDL particle number (-0.64 μmol/L; 95% CI -1.01 to -0.26).

The authors note that HDL particle numbers in MESA Air have been independently linked with carotid atherosclerosis and coronary heart disease.

The effect of HDL lowering linked with black carbon was seen in both sexes but was more pronounced in women (-2.63 mg/dL, 95% CI -4.46 to -0.81) than in men (-0.65 mg/dL, 95% CI -2.14 to 0.84).

In addition, they write, there was a stronger relationship between 3-month exposure to PM2.5. and HDL particle number (-0.71 μmol/L, 95% CI -1.33 to -0.09) in women than in men (-0.48 μmol/L, 95% CI -0.93 to -0.02; P for interaction=0.02).

It's the first large observational study to show an association between air-pollution exposure and HDL particle number, the authors write.

Bell had no relevant financial relationships. Disclosures for the coauthors are listed in the paper.

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