Inflammation that starts in the lungs may then spread to the brain, she said.
The new research "is a little worrisome for those of us living in cities," said Dr. Lawrence Wechsler, an expert unaffiliated with the study, and chairman of the department of neurology at the University of Pittsburgh.
While other research has suggested a possible connection between pollution and brain health, "this is the most solid evidence we've had to date that there might really be some association between the low levels of pollution people are exposed to and some kind of long-term brain injury," Weschler said.
One big concern for seniors involves the 46 percent increase in mini-strokes, said Dr. Beate Ritz, chair of the department of epidemiology at the Center for Occupational and Environmental Health at UCLA's Fielding School of Public Health. Ritz is also unaffiliated with the new study.
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"Mini-strokes don't cause as much damage as a larger stroke, but sometimes they can do nasty things depending on where they are [in the brain]," Ritz said. "They won't leave you totally disabled but they can make your health-related quality of life much lower. "
They are also insidious, Ritz said, because you often aren't aware you're having one. "You might be a little more dizzy today and then lose a little more vision tomorrow. And people tend to attribute that to aging instead of knowing what happened."