Beijing's Third Ring Road is shrouded in haze on 12 January 2013 as the city's air pollution reached hazardous levels. Photo: Reuters

By Marilyn Malara
25 April 2015

BOSTON (UPI) – A new study confirms that long-term exposure to air pollution –even at low levels – can lead to brain damage that precedes other neurological disorders associated with old age.

Investigator Elissa Wilker of the Cardiovascular Epidemiology Research Unit at Beth Israel Deaconess Medical Center and the Harvard T.H. Chan School of Public Health, along with colleagues, published their findings in the journal Stroke.

The team tested the effects of long-term exposure to PM2.5, or fine particles found in the air like dust, dirt, soot, smoke, and liquid that measure less than 2.5 micrometers in diameter. Between 1995 and 2005, they used magnetic resonance imaging (MRI) to analyze the brain health of more than 900 healthy adults over the age of 60 living around Boston and New York.

They found that a PM2.5 increase of 2 micrograms per cubic meter of air, a common level in metropolitan regions, was linked to a 0.32 percent reduction in total brain volume and a 46 percent increased risk of covert brain infarcts, a type of so-called "silent" stroke, which often presents no outward symptoms but increases the risk of future strokes. These covert brain infarcts occur deep within the brain and are linked to poor cognitive function and dementia, Wilker says. [more]

Prolonged exposure to air pollution linked to brain damage, new study finds

DALLAS, April 23, 2015 – Long-term exposure to fine particle air pollution may cause subtle structural changes in the brain that could precede cognitive impairment and hidden brain damage, according to research in the American Heart Association journal Stroke.

Fine particle air pollution – smaller than 2.5 micrometers in diameter (PM2.5) – may be the most common and hazardous type of air pollution. It comes from burning wood or coal, car exhaust and other sources.

“Long-term exposure to air pollution showed harmful effects on the brain in this study, even at low levels, particularly with older people and even those who are relatively healthy,” said Elissa H. Wilker, Sc.D., study lead author and researcher in the Cardiovascular Epidemiology Research Unit at Beth Israel Deaconess Medical Center and the Harvard T.H. Chan School of Public Health in Boston.

Researchers analyzed 943 adults in the Framingham Offspring Study, who were relatively healthy and free of dementia and stroke. The participants lived in the greater Boston area and throughout New England and New York — regions where air pollution levels are low compared to other parts of the nation and the world.  

During 1995-2005, researchers used magnetic resonance imaging (MRI) to determine the effect of long-term exposure to air pollution on markers of brain structure. They found a 2 microgram per cubic meter of air (μg/m3) increase in PM2.5, a range commonly observed across a metropolitan region, was associated with a 0.32 percent smaller total cerebral brain volume and a 46 percent higher risk of covert brain infarcts, a type of silent stroke.

“The magnitude of association that we observed for brain volume was similar to approximately one year of brain aging,” Wilker said.

Fundamental changes in the structure of the cerebral brain volume and smaller brain size are markers of age-associated brain atrophy.

“We found that people who live in areas where there are higher levels of air pollution had smaller total cerebral brain volume and were more likely to have evidence of covert brain infarcts,” said Wilker, who is also an instructor of medicine in the Harvard Medical School.

The small infarcts, typically located in deep regions of the brain, have been associated with neurological abnormalities, poorer cognitive function, dementia, and are thought to reflect small vessel disease, she said. 

Fine particulate matter affects more people than any other pollutant, with chronic exposure causing the most deaths from serious disease, according to the World Health Organization (WHO). PM2.5 may trigger disease because the particles penetrate into the alveoli of the lungs. Fine particulate matter can also contribute to the narrowing of arteries that supply blood to the brain.

These findings are consistent with prior studies that have shown an association between long-term pollution exposure and living close to major roads and first-time stroke and poorer cognitive function in older adults.

To educate the public about daily air quality levels, including ozone and particulate matter levels, the EPA provides daily updates at and in many newspapers across the country.

Co-authors are Sarah Preis, Sc.D.; Alexa Beiser, Ph.D.; Philip Wolf, M.D.; Rhoda Au, Ph.D.; Itai Kloog, Ph.D.; Wenyuan Li, M.S.; Joel Schwartz, Ph.D.; Petros Koutrakis, Ph.D., Charles DiCarli, M.D.; Sudha Seshadri, M.D.; and Murray Mittleman, M.D.

The National Institutes of Health and the Environmental Protection Agency funded the study.

Long-term exposure to air pollution may harm your brain

ABSTRACT: Background and Purpose—Long-term exposure to ambient air pollution is associated with cerebrovascular disease and cognitive impairment, but whether it is related to structural changes in the brain is not clear. We examined the associations between residential long-term exposure to ambient air pollution and markers of brain aging using magnetic resonance imaging.

Methods—Framingham Offspring Study participants who attended the seventh examination were at least 60 years old and free of dementia and stroke were included. We evaluated associations between exposures (fine particulate matter [PM2.5] and residential proximity to major roadways) and measures of total cerebral brain volume, hippocampal volume, white matter hyperintensity volume (log-transformed and extensive white matter hyperintensity volume for age), and covert brain infarcts. Models were adjusted for age, clinical covariates, indicators of socioeconomic position, and temporal trends.

Results—A 2-μg/m3 increase in PM2.5 was associated with −0.32% (95% confidence interval, −0.59 to −0.05) smaller total cerebral brain volume and 1.46 (95% confidence interval, 1.10 to 1.94) higher odds of covert brain infarcts. Living further away from a major roadway was associated with 0.10 (95% confidence interval, 0.01 to 0.19) greater log-transformed white matter hyperintensity volume for an interquartile range difference in distance, but no clear pattern of association was observed for extensive white matter.

Conclusions—Exposure to elevated levels of PM2.5 was associated with smaller total cerebral brain volume, a marker of age-associated brain atrophy, and with higher odds of covert brain infarcts. These findings suggest that air pollution is associated with insidious effects on structural brain aging even in dementia- and stroke-free persons.

Long-Term Exposure to Fine Particulate Matter, Residential Proximity to Major Roads and Measures of Brain Structure

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