Pollutants in the air from vehicles and the burning of fossil fuels have been linked to brain damage known to lead to other neurological disorders associated with old age, a new study finds. Photo by Stephen Shaver/UPI.

BOSTON, April 25 (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.

"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," Wilker said in a press release.

The World Health Organization estimates around 7 million people died in 2012 due to air pollution; about 40 percent of those deaths were linked to stroke.

"We now plan to look at more the impact of air pollution over a longer period," said Wilker, "its effects on more MRI sensitive measures, on brain shrinkage over time and other risks including of stroke and dementia."