Is Dirty Air Damaging the Brains of Some City Dwellers?

City air pollution could hurt your brain, Harvard researchers suggested Thursday.

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.

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Smog over Beijing, China.
Terry Tamminen for CNBC
Smog over Beijing, China.

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."

This city could ban diesel cars
This city could ban diesel cars   

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."