Growing Evidence Linking Air Pollution With Cardiovascular Disease: AHA

May 11, 2010

May 11, 2010 (Ann Arbor, Michigan) — Short-term exposure to air pollution, ranging from just a few hours to weeks, can trigger cardiovascular-disease–related mortality and nonfatal events, including MI, heart failure, arrhythmias, and stroke, according to a new updated scientific statement from the American Heart Association [1].

The increase in pollution-associated cardiovascular morbidity and mortality primarily affects susceptible individuals, such as the elderly, those with coronary artery disease, and possibly those with diabetes, while some data suggest that women and obese individuals might also be at higher risk of clinical events.

These are some of the conclusions reached by the chair of the AHA writing committee, Dr Robert Brook (University of Michigan, Ann Arbor), and colleagues, who put together the scientific statement on particulate-matter (PM) air pollution and cardiovascular disease. Now published online May 10, 2010 in Circulation, the new report is an update to the 2004 scientific statement regarding air pollution and cardiovascular disease, one that was needed because of numerous studies that expanded the "understanding of this association and further elucidated the physiological and molecular mechanisms involved."

"There is mounting evidence from a rapid growth of published data since the previous statement related to the harmful cardiovascular effects of air pollution," write Brook and colleagues. "Most, but not all, epidemiological studies corroborate the elevated risk for cardiovascular events associated with exposure to fine particulate matter <2.5 µm (PM2.5) in aerodynamic diameter. PM2.5 generally has been associated with increased risks of myocardial infarction, stroke, arrhythmia, and heart-failure exacerbation within hours to days of exposure in susceptible individuals. Several new studies have also demonstrated that residing in locations with higher long-term average PM levels elevates the risk for cardiovascular morbidity and mortality."

Cardiovascular Mortality and Air Pollution

The major source of PM air pollution is fossil-fuel combustion from industry, traffic, and power generation. Heating and cooking with solid fuels, such as coal, are also sources of PM, particularly in certain parts of the world. The AHA review focused explicitly on PM because the majority of air-pollution studies have addressed its cardiovascular effects, making it possible for the writing committee to develop consensus opinions and make recommendations.

In the updated statement, the writing committee states there is a small but consistent association between short-term exposure to PM2.5 and premature death and a strong level of evidence supporting the link between air pollution and ischemic heart disease. Also, there is a moderate association between air pollution and stroke and a modest level of evidence linking PM2.5 with peripheral vascular diseases.

Overall, they conclude that long-term exposure to elevated concentrations of ambient PM2.5 at levels in the present environment likely reduces life expectancy at the population level from several months to a few years. "Given that PM2.5 is most strongly associated with cardiovascular deaths in the cohort studies, the reduced life expectancy is most likely predominantly due to excess cardiovascular mortality," write Brook and colleagues.

Based on the level of evidence, the writing group suggests that clinicians can take several precautionary measures, although they add that these have not been tested or proven to reduce mortality. However, the recommendations are "practical and feasible measures to reduce exposures to air pollution and therefore potentially lower the associated cardiovascular risk." These recommendations include:

  • Evidence-based treatment of traditional cardiovascular risk factors with the intention of lessening the susceptibility of patients to air-pollution exposures.

  • Education of cardiovascular disease patients about the risks of air pollution.

  • Consideration of educating patients without cardiovascular disease but who might be at high risk, such as the elderly, those with multiple risk factors, or individuals with diabetes.

  • On the basis of the air-quality index, making prudent recommendations for reducing exposure and limiting activity, based on patient risk, when the air quality is poor.

At the present time, because of limited evidence, the committee makes no specific recommendations about more aggressive measures, such as wearing face masks or installing PM filters in households. It also stresses that despite the evidence supporting causal relationship between PM2.5 and cardiovascular mortality, continued research is needed.

In addition to focusing on the effects of PM on cardiovascular disease, the review also summarized the effects of ambient air pollution on subclinical pathophysiological responses, such as systemic inflammation, oxidative stress, thrombosis and coagulation, blood-pressure effects, vascular function, heart-rate variability, and atherosclerosis.