Long-Term Exposure to Invisible Pollutants May Harm Endothelial Function

October 29, 2012

SEATTLE — Long-term exposure to air pollution, in the form of fine particulate matter, is associated with reduced endothelial function in the brachial artery, new results from the Multi-Ethnic Study of Atherosclerosis (MESA) air study show [1]. These are the first epidemiological data to document such a finding, say Dr Ranjini M Krishnan (University of Washington, Seattle) and colleagues in their paper published online October 24, 2012 in the Journal of the American College of Cardiology.

The research may provide a clue as to how long-term exposure to fine particulate matter leads to functional changes in the endothelium, which could, in turn, partly explain the risk of cardiovascular events previously associated with exposure to air pollution, say Krishnan et al.

In an accompanying editorial [2], Drs Robert D Brook (University of Michigan, Ann Arbor) and Sanjay Rajagopalan (Ohio State University College of Medicine, Columbus) say the magnitude of vascular dysfunction seen here, while "seemingly small," was "analogous to the adverse effects of smoking or five years of aging."

And these results are from cities in the US that have "comparatively low air-pollution concentrations," they note. "When one considers the fact that fine-particulate-matter (<2.5 µm in diameter; PM2.5) air-pollution levels often average five- to 10-fold higher across numerous regions populated by billions of people worldwide, the grave public-health consequences of air pollution corroborated by the findings of this important study deserve serious and immediate attention."

Nonsmokers, the Young, and Hypertensives May Be More Susceptible

In their cross-sectional, observational study, Krishnan and colleagues measured flow-mediated dilation (FMD) of the brachial artery using ultrasound at the initial examination in 3040 participants in MESA air study between the years 2000 and 2002. Using linear effects, they correlated this with long-term PM2.5 concentrations--an estimated average for the year 2000 at each participant's residence using spatiotemporal modeling--and adjusted for demographic characteristics, traditional cardiovascular risk factors, and sonographers.

This magnitude of vascular dysfunction, although seemingly small, was analogous to the adverse effects of smoking or five years of aging.

Senior author Dr Joel D Kaufman (University of Washington) told heartwire : "We were making the assumption that the air pollution in 2000 roughly corresponds to how it is each year, and 2000 was convenient because prior to this there wasn't an extensive network of monitoring for PM2.5."

A 3-µg/m3-higher annual average PM2.5 exposure was associated with a significant 0.3% reduction in FMD. FMD was not significantly associated with short-term variation in PM2.5, however, which likely illustrates the fact that cumulative exposures probably have more discernible effects, say the editorialists.

There's a mystery about how you get from air pollution exposure to having CV disease events. The finding of impairment in endothelial function is really just a confirmation of how you might get there.

Kaufman said: "The message of this study is that there have been these epidemiological observations that have shown an effect on cardiovascular disease incidence from PM2.5, and there's a mystery about how you get from air-pollution exposure to having cardiovascular disease events. The finding of impairment in endothelial function is really just a confirmation on the pathway of how you might get there."

Brook and Rajagopalan say this is one of the largest investigations linking air-pollution exposure with CV imaging end points, and the findings support previous assertions that women may be more susceptible to air pollution, as well as pointing to other potentially "at-risk" groups, including nonsmokers, younger participants, and those with hypertension.

The findings corroborate the contention that air pollution is an insidious and omnipresent cardiovascular risk factor, and that even "invisible" elements--such as chronic exposure to low levels of air pollution--"can have significant adverse effects on CV health," they conclude.

The authors and editorialists have no conflicts of interest