Air pollution may increase risk for stroke, cognitive decline

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Exposure to air pollution may have serious cognitive and cardiovascular health consequences, even at levels currently deemed acceptable by the U.S. Environmental Protection Agency (EPA), data from two studies published in the Archives of Internal Medicine suggest.

Gregory Wellenius, ScD, of Brown University in Providence, R.I., and colleagues found that short-term exposure to fine particulate matter at levels the EPA considers safe can increase the risk for ischemic stroke.

In the other study, Jennifer Weuve, ScD, of Rush University Medical Center in Chicago, and colleagues determined that long-term exposure to fine particulate matter was associated with significantly expedited cognitive decline among older women.

The first report from Wellenius et al “adds to the already strong evidence” linking air pollution to cardiovascular effects, Rajiv Bhatia, MD, MPH, from the Department of Environmental Health at the San Francisco Department of Public Health, wrote in an accompanying editorial.

Furthermore, the findings on particulate matter and cognitive decline suggest the health burden of exposure to air pollution may not be fully understood.

Bhatia concluded that more effort is needed to curb human exposure to air pollution at the community level, as well as through “more stringent and creative regulatory initiatives, and political support.”  He called on healthcare providers to advocate for these protections.

To determine the association between fine particulate matter (defined as particles less than 2.5 micrometers in diameter) and stroke, Wellenius and colleagues analyzed data from 1,705 patients admitted to a single institution in Boston with neurologist-confirmed ischemic stroke between April 1, 1999 and Oct. 31, 2008.

The study period included only days in which the air quality was good or moderate as measured at a Central Monitoring Station. EPA regulations define good air quality as concentrations of fine particulate matter at or below 15 micrograms per cubic meter of air, and moderate as between 15 and 40 micrograms. 

The researchers excluded 11 days on which air pollution surpassed 40 micrograms per cubic meter.

They found that the estimated odds ratio of stroke onset was 1.34 following a 24-hour period during which air quality was classified as moderate compared with a similar, good-air quality timeframe  (95% CI: 1.13 to 1.58; P<0.001).  This association was linear, with the association between stroke onset and fine particulate matter strongest within 12 hours of exposure among those with large-artery atherosclerosis or small-vessel occlusion.

When they looked at the type of particulate matter, the researchers determined that the risk was more strongly associated with traffic pollution, such as black carbon and NO2, versus non-traffic associated particulate matter.

In the cognition study, Weuve and colleagues examined data from 19,049 women aged 70 years or older without a history of stroke, who participated in the Nurses Health Study between 1995 and 2001 and agreed to undergo cognitive testing.

The researcher performed cognitive testing via telephone three times during the study period, at two-year intervals looking for associations between cognitive changes in both fine (smaller than 2.5 micrometers in diameter) and course particulate matter exposure (2.5-10 micrometers).

Significantly faster cognitive decline occurred among participants with higher levels of long-term exposure to both grades of pollutants, the researchers determined.

For every 10 micrograms per cubic meter increase in long-term exposure to coarse particles, participants experienced an average 0.020 unit decline in global score during a two-year period. Similarly, the two-year global score decline for every 10 microgram per cubic meter increase in fine particle exposure was 0.018. These changes were on par with differences in the cognitive trajectories of women approximately two years apart in age, the researchers noted.

“These associations were present at levels of PM exposure typical in many areas of the United States. 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 et al wrote.

Wellenius GA et al. Arch Intern Med. 2012; 172(3): 229-234.

Weuve J et al.  Arch Intern Med. 2012; 172(3): 219-227.

Bhatia R.  Arch Intern Med. 2012; 172(3): 227-228.

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