Air Pollution and Cognitive Decline

Airborne pollution can have serious consequences for the brain and the heart even at typical levels of exposure, according to the results of two studies published in the Feb. 13 issue of Archives of Internal Medicine.

In one analysis, researchers led by Gregory Wellenius, ScD, of Brown University in Providence, R.I., found that short-term exposure to fine particulate matter – even at levels allowed by the EPA – can increase the risk of ischemic stroke.

In the other study, a team led by Jennifer Weuve, ScD, of Rush University Medical Center in Chicago, and colleagues found that long-term exposure to particulate matter speeded up cognitive decline in older women.

The first report "adds to the already strong evidence linking (particulate matter) to cardiovascular effects," wrote Rajiv Bhatia, MD, of the San Francisco Department of Public Health, in an accompanying commentary.

And, he added, the cognition study suggests that "we may not fully understand the breadth of (particulate matter) health burdens."

Bhatia concluded that controlling particulate matter is technically feasible, but needs "increased efforts to assess exposure at the community level, more stringent and creative regulatory initiatives, and political support."...They also found that the relationship between higher particulate levels and increased risk of stroke was linear, strongest within 12 hours of exposure, and was seen among patients with strokes caused by large-artery atherosclerosis or small-vessel occlusion but not cardioembolism.

The risk was more strongly associated with markers of traffic pollution – such as black carbon and NO₂ – than with particles linked to nontraffic sources, they reported.

Although the findings add to the evidence linking stroke and air pollution, there are some "unique" aspects, according to Robert Brook, MD, of the University of Michigan Ann Arbor, and Sanjay Rajagopalan, MD, of the Ohio State University Medical Center in Columbus.

Specifically, they noted in an accompanying commentary, "the extremely rapid increase in stroke risk is an important novel insight" that suggests that current regulatory focus on daily and yearly average concentrations may be missing the boat.

For the cognition study, Weuve and colleagues turned to the long-running Nurses' Health Study, which began in 1976 with more than 121,000 participants...Analysis showed that higher levels of long-term exposure to both grades of pollution were associated with "significantly faster cognitive decline," the researchers found. 

The associations, they reported, were found at pollution levels typical in many areas, suggesting that pollution control might be a way to reduce the "future population burden of age-related cognitive decline, and, eventually, dementia."