CardioExchange Archive

Epidemiology studies have provided powerful evidence linking air pollution to cardiovascular disease, especially MI and stroke. By some estimates, air pollution may be responsible for 3.2 million deaths each year, most from cardiovascular causes.

At first glance, a new study published in Heart appears to cast doubt on this association. Analyzing U.K. data from more than 400,000 MIs, 2 million hospital admissions, and 600,000 CV deaths, London-based researchers turned up conflicting and difficult-to-interpret findings concerning the effects of air pollution on cardiovascular health. Surprisingly, the researchers did not find a significant association between short-term exposure to air pollution and the risk for either MI or stroke. But they did turn up some significant associations. Nitrogen dioxide was linked to hospital admissions for CV disease, non-MI CV disease, arrhythmias, and heart failure. PM2.5 — particulate matter with diameters smaller than 2·5 μm — was linked to deaths from arrhythmias, atrial fibrillation, and pulmonary embolism.

But although the study failed to elucidate the pathways by which air pollution may lead to cardiovascular events, the confusing results may well reflect a broadly favorable trend in pollution reduction in the U.K. In an accompanying editorial, Anoop Shah and David Newby point out that air pollution in the study appeared to be quite moderate compared with “many of the megacities across the world,” which have PM2.5 levels 10-20 times the median level measured in the U.K. in the current study.

The title of their editorial is, “Less Clarity as the Fog Begins to Lift.” They conclude: “Some have suggested that associations with adverse cardiovascular events persist even at low pollutant concentrations, but as air quality continues to improve, the adverse impact on health will decline. The current lack of consistent associations with contemporary U.K. data may suggest that as the fog begins to clear, the adverse health effects of air pollution are starting to have less of an impact and are more difficult to delineate.”