Long-Term Exposure to Air Pollution May Pose Risk to Brain.

Air pollution, even at moderate levels, has long been recognized as a factor in raising the risk of stroke. A new study led by scientists from Beth Israel Deaconess Medical Center and Boston University, including researchers from the School of Public Health, suggests that long-term exposure can cause damage to brain structures and impair cognitive function in middle-aged and older adults.

Writing in the journal Stroke, a research team that includes Alexa S. Beiser, professor of biostatistics at SPH and of neurology at the School of Medicine, and Sarah R. Preis, SPH research assistant professor of biostatistics, found evidence of smaller brain structure and of covert brain infarcts—a type of “silent” ischemic stroke resulting from a blockage in the blood vessels supplying the brain—in a study of more than 900 participants of the Framingham Heart Study.

The study evaluated how far participants lived from major roadways and used satellite imagery to assess prolonged exposure to ambient fine particulate matter, defined as having a diameter of 2.5 millionth of a meter, referred to as PM2.5. These particles come from a variety of sources, including power plants, factories, trucks and automobiles, and the burning of wood. They can travel deeply into the lungs and have been associated in other studies with increased numbers of hospital admissions for cardiovascular events such as heart attacks and strokes.

Study participants were at least 60 years old and were free of dementia and stroke. The evaluation included total cerebral brain volume, a marker of age-associated brain atrophy; hippocampal volume, which reflects changes in the area of the brain that controls memory; white matter hyper-intensity volume, which can be used as a measure of pathology and aging; and covert brain infarcts.

The study found that an increase of only 2µg per cubic meter in PM2.5, a range commonly observed across metropolitan regions in New England and New York, was associated with being more likely to have covert brain infarcts and smaller cerebral brain volume, equivalent to approximately one year of brain aging.

“This study shows that for a 2 microgram per cubic meter of air (μg/m3) increase in PM2.5, a range commonly observed across major US cities, on average participants who lived in more polluted areas had the brain volume of someone a year older than participants who lived in less polluted areas,” said Sudha Seshadri, a professor of neurology at the School of Medicine and senior investigator on the Framingham Study.

“This is concerning, since we know that silent strokes increase the risk of overt strokes and of developing dementia, walking problems, and depression.”

The research team includes scientists from the Exposure Epidemiology and Risk Program in the Department of Environmental Health at the Harvard T.H. Chan School of Public Health (HSPH); the Department of Geography and Environmental Development, Ben-Gurion University of the Negev, Beer Sheva, Israel; the Department of Epidemiology of HSPH; and the Department of Neurology and Center for Neuroscience, University of California, Davis.

Submitted by: Lisa Chedekel