Studies link air pollution, CV events

New data suggest that pollution in the air may be associated with increased risks for MI and stroke.

A review and meta-analysis of previous studies found that short-term exposure (less than 7 days) to all major air pollutants, with the exception of ozone, is significantly associated with an increased risk for MI. Researchers in Paris reviewed 34 studies conducted between 1988 and 2011 that analyzed the association between air pollutants and MI risk. Results showed that carbon monoxide (RR=1.048; 95% CI, 1.026-1.070), nitrogen dioxide (RR=1.011; 95% CI, 1.006-1.016), sulfur dioxide (RR=1.010; 95% CI, 1.003-1.017), particulate matter with an aerodynamic diameter of 10 mcm (PM₁₀) or less (RR=1.006; 95% CI, 1.002-1.009) and particulate matter with an aerodynamic diameter of 2.5 mcm (PM_2.5) or less (RR=1.025; 95% CI, 1.015-1.036) were significantly associated with an increase in MI risk. However, ozone pollutants (RR=1.003; 95% CI, 0.997-1.010) were not associated with an increased risk. A subgroup analysis based on study quality showed similar results to the overall analysis.

Gregory A. Wellenius

“Our meta-analysis is the first, to our knowledge, to evaluate the quality and magnitude of associations between short-term exposure to major air pollutants and the risk of MI,” Hazrije Mustafic, MD, MPH, of the University Paris Descartes, INSERUM Unit 970, Paris, and colleagues wrote in the Journal of the American Medical Association. “Further research is needed to determine whether effective interventions that improve air quality are associated with a decreased incidence of MI.”

Pollutants and stroke risk

In other research, two studies published in Archives of Internal Medicine report an association between air quality and risk for acute ischemic stroke and cognitive decline in older women.

Gregory A. Wellenius, ScD, of Brown University, and colleagues evaluated the association between changes in fine particular matter air pollution (particulate matter <2.5 mcm/m³) levels and risk for ischemic stroke. The study included more than 1,700 patients (mean age, 73 years) who were hospitalized at Beth Israel Deaconess Medical Center between 1999 and 2008. Risk for ischemic stroke onset and particulate matter levels in the hours and days preceding each event were assessed. During the study period, PM_2.5 levels in the Boston area did not exceed current Environmental Protection Agency Air Quality Index standards, the researchers noted.

On days classified as “moderate” by the EPA (particulate matter <2.5 mcm/m³; PM_2.5), risk for ischemic stroke was 1.34 (95% CI, 1.13-1.58) compared with days classified as “good” (particulate matter <15 mcm/m³). When researchers considered particulate matter levels as a continuous variable, estimated OR of ischemic stroke onset was 1.11 (95% CI, 1.03-1.20) per interquartile range increase in particulate matter levels.

In a second study, Jennifer Weuve, MPH, ScD, of Rush University Medical Center, and colleagues evaluated air pollution in relation to cognitive decline in older women using a study population from the Nurses’ Health Study Cognitive Cohort, which included more than 19,000 US women aged 70 to 81 years.

“In this large, prospective study of older women, higher levels of long-term exposure to both PM_2.5-10 and PM_2.5 were associated with significantly faster cognitive decline,” the researchers wrote.

Results showed a 20year decline on global cognitive function scores in women with the highest levels of exposure to particulate matter levels. These associations were present at levels of particulate matter exposure typical in many areas of the United States, according to the researchers.

“Therefore, if our findings are confirmed in other research, air pollution reduction is a potential means for reducing the future population burden of age-related cognitive decline and, eventually, dementia,” Weuve and colleagues concluded.

Burden of pollution on health

Inflammation, abnormal regulation of the cardiac autonomic system, and increased blood viscosity and vasoconstrictors due to air pollution were identified as possible mechanisms for the associations found in the study by Mustafic and colleagues. However, the researchers acknowledged that these associations are relatively small compared with associations of classic MI risk factors such as smoking, hypertension or diabetes.

In an editorial published in JAMA, Robert D. Brook, MD, of the University of Michigan, and Sanjay Rajagopalan, MD, of the Dorothy M. Davis Heart and Lung Research Institute at Ohio State University Medical Center, said these data should serve as a reminder that “clinical events could be initiated by even briefer sub-daily periods of PM_2.5 inhalation.

“With the availability of improving pollutant data, future studies should aim to elucidate the health effects of sub-daily time windows of exposure. If similar findings are corroborated or found for other diseases, those who create air quality standards might need to consider the difficult task of curbing sub-daily particulate matter concentrations, as they did to create the existing 8-hour ozone regulations,” Brook and Rajagopalan wrote.

In another commentary published in Archives of Internal Medicine, Rajiv Bhatia, MD, MPH, of the San Francisco Department of Public Health, said, “Improved control of human exposure to PM_2.5 is technically feasible but will require increased efforts to assess exposure at the community level, more stringent and creative regulatory initiatives and political support. Physicians, who are already responding to the human consequences of particulate pollution, can be effective advocates for these protections.”– by Katie Kalvaitis and Casey Murphy

For more information:

• Bhatia R. Arch Intern Med. 2012;172:227-228.
• Brook R. Arch Intern Med. 2012;172:235-236.
• Mustafic H. JAMA. 2012;307:713-721.
• Wellenius G. Arch Intern Med. 2012;172:229-234.
• Weuve J. Arch Intern Med. 2012;172:219-227.

Disclosure: Drs. Bhatia, Brook, Mustafic, Rajagopalan, Wellenius and Weuve report no relevant financial disclosures.

Follow CardiologyToday.com on Twitter.