Air Pollution Tied to Acute Stroke, Cognitive Decline

Breathing in particulate matter, even at levels deemed safe by Environmental Protection Agency (EPA) standards, may raise the risk for acute ischemic stroke and for cognitive decline, 2 new studies suggest.

In an accompanying commentary, Rajiv Bhatia, MD, MPH, from the San Francisco Department of Public Health in California, notes that the reported association between ambient fine particulate matter, defined as less than 2.5 μm (PM 2.5), and ischemic stroke "adds to the already strong evidence" linking PM 2.5 to cardiovascular effects, and adds that the analysis on cognitive function shows that "we may not fully understand the breadth of PM health burdens."

"The strong and growing evidence on the harms of PM 2.5 demands scrutiny of societal efforts to reduce exposure," Dr. Bhatia concludes.

The studies and commentaries were published online February 13 in the Archives of Internal Medicine.

In the first study, Gregory A. Wellenius, ScD, from the Center for Environmental Health and Technology, Brown University, Providence, Rhode Island, and colleagues reviewed the medical records of 1705 patients admitted to Beth Israel Deaconess Medical Center in Boston, Massachusetts, between 1999 and 2008 with acute ischemic stroke, and estimated the hour when the stroke symptoms first occurred.

"Using hourly measurements of ambient air pollution from the nearby Harvard School of Public Health environmental monitoring station, we found that the risk of stroke was linked to levels of ambient air particles," Dr. Wellenius told Medscape Medical News.

The estimated odds ratio (OR) of ischemic stroke onset was 1.34 (95% confidence interval [CI], 1.13 -1.58; P < .001) after a 24-hour period with PM 2.5 levels in the "moderate" range by EPA standards (15 - 40 μg/m3) compared with a similar period with levels in the "good" range (≤15 μg/m3). During the study, PM 2.5 levels in the Boston area did not exceed current EPA standards.

"We also found that the increased risk of stroke peaked 12 to 14 hours after levels of ambient air particles went up — a shorter time interval than previously found," Dr. Wellenius said.

In a second invited commentary, Robert D. Brook, MD, from the University of Michigan, Ann Arbor, and Sanjay Rajagopalan, MD, from the Ohio State University Medical Center in Columbus, say these findings are important because current US and World Health Organization air quality standards focus only on daily and annual PM 2.5 mean concentrations.

"The findings by Wellenius et al remind us that clinical events could be initiated by even briefer subdaily periods of PM2.5 inhalation," they write.

The risk was most strongly associated with components of traffic pollution, mainly black carbon and nitrogen dioxide. Ozone or sulfates were not associated with ischemic stroke risk.

To continue reading, click the link below.