Brain scans showed that seniors exposed to higher levels of the kind of small particle pollution that can come from car exhaust had a higher risk of mini-strokes and a smaller brain volume compared to those living in less-polluted areas, according to the study published in the journal Stroke.

The new findings are "provocative," said the study's lead author, Elissa Wilker, an instructor of medicine at the Harvard Medical School and a researcher at the Cardiovascular Epidemiological Research Unit at the Beth Israel Deaconess Medical Center. In fact, dirty city air seems to cause the equivalent of a full year's worth of aging inside the brain.

"It suggests that subtle but potentially harmful effects are going on: The effect on the brain of being one year older is similar to the effect of pollution," she said.



Wilker and her colleagues reexamined MRI scans done between 1995 and 2005 on 943 adults aged 60 and older who were relatively healthy, free of dementia and who had not had a stroke. The scans were done as part of the Framingham Offspring Study.



Information from the scans was then correlated with pollution data gleaned from satellite observations.



The researchers found a startling result when they compared seniors living in the most-polluted areas to those dwelling in spots with the cleanest air: a 46 percent higher risk of mini-strokes and a 0.32 percent reduction in brain volume.

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Wilker doesn't yet know how pollution could be harming the brain. "That's the million dollar question," she said. "We think when you breathe those particles in they can cause inflammation."