Long-term exposure to polluted air can make your brain a year older, leading to thinking and memory problems and other hidden damage.

This is bad news because, according to State of the Air Report of the American Lung Cancer Association, 60 percent of Americans live in areas with unhealthy levels of air pollution. The Environmental Protection Agency (EPA) has listed the known serious health threats brought by air pollution, which include respiratory problems, early death, cardiovascular problems, central nervous system problems and reproductive and developmental problems. Earlier studies also associated air pollution with the increased risks of autism, anxiety, stroke, premature deaths, and other health issues.

Now, researchers at the Harvard Medical School in Boston are providing evidence that long-term exposure to air pollution is harmful to the brain. They looked at the data of 953 participants living in Boston, New England and New York. These participants were free of dementia and stroke at the start of the study period.

During the 10-year follow-up period, the researchers reviewed the brain scans of the participants to monitor changes in their brains. They observed that the brain volume of those from areas where air pollution levels are higher became 0.32 percent smaller than those with lesser exposure. Smaller brain volume was previously associated to poorer cognitive function, which can lead to thinking and memory problems. The risk of silent stroke also increased by 46 percent.

The study is the first to link air pollution to changes in the brain volume of older adults. 

"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," Elissa H. Wilker, 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, said in a press release.

The study was published in the April 23 issue of the journal Stroke.