Could Air Pollution Lead to Brain Damage?
Long-term exposure to one of the most common and hazardous forms of air pollution was associated with slight structural changes in the brain that could lead to cognitive impairment, according to a new study in the journal Stroke.
Smaller than 2.5 micrometers in diameter (PM2.5), fine particle air pollution comes from a variety of sources, including power plants, factories, trucks and automobiles, and wood or coal burning.
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“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,” says lead study author Elissa H. Wilker, ScD, a 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.
Wilker and her colleagues studied 943 adults who were part of the Framingham Offspring Study. These participants were at least 60 years old, free of dementia and stroke, and lived in the greater Boston area and throughout New England and New York. Using data collected from 1995 to 2005, researchers looked at the effects of long-term exposure to air pollution on markers of brain structure as measured by MRI testing.
“Although air pollution levels in this region are relatively low compared to levels observed in other places, we found that people who lived in areas with higher levels of air pollution had smaller brain volumes, and higher risk of silent strokes,” Wilker says.
Their findings showed that an increase of 2 micrograms per cubic meter of air in PM2.5—a range commonly observed across a metropolitan region—was associated with a 0.32% smaller total cerebral brain volume and a 46% higher risk of covert brain infarcts.
Covert brain infarcts have been associated with neurological abnormalities, poorer cognitive function, onset of dementia, and are thought to reflect small-vessel disease, while smaller total cerebral brain volume is a marker of age-associated brain atrophy.
While the researchers are still learning about the mechanisms that may explain these associations, Wilker says they believe that inflammatory pathways are likely important and that reduced blood flow to the brain may lead to damage that can have functional effects.
“Smaller particles (of air pollution) may be particularly toxic because they can travel more deeply and get trapped in the lungs,” Wilker explains. “Over time, they may cause respiratory symptoms, and also systemic inflammation, cardiovascular disease, and cerebrovascular effects.”
Wilker and her colleagues emphasize that these findings require further investigation and that it will be important to see whether future studies confirm or refute them.
“In the future, we hope to investigate the impact of air pollution over a longer period, and to evaluate its effect on more sensitive MRI measures and other factors including stroke and dementia,” she says.
—Colleen Mullarkey
Reference
Wilker EH, Preis SR, Beiser AS, Wolf PA, Au R, Kloog I, Li W, et al. Long-term exposure to fine particulate matter, residential proximity to major roads and measures of brain structure. Stroke. 23 April 2015. [Epub ahead of print].