New research suggests that exposure to ambient air pollution is associated with adverse health effects. In urban areas, air pollution is a mixture of gaseous pollutants and particulate matter that derives from sources mostly related to burning fossil fuels. When inhaled, small-particle air pollution of <10 μm in diameter can travel through the circulatory system and ultimately damage the heart, lungs, and brain. As people live longer and the population shifts to urban metropolitan areas, we need to understand the health risks from environmental exposures and the potential impact on cognitive impairment.

To examine the adverse effects of ambient fine particulate matter <2.5 μm in diameter (PM2.5) on brain volume in older women, researchers prospectively studied 1403 community-dwelling older women without dementia who were enrolled in the Women’s Health Initiative Memory Study (WHIMS) from 1996 through 1998. Participants underwent structural brain magnetic resonance imaging (MRI) at age 71 to 89 years (in 2005–2006). PM2.5 in the women’s areas of residence was measured between 1999 and 2006.

Women with greater exposure to PM2.5 had significantly smaller WM but not GM volumes. For each interquartile increment (3.4 μ/m3) of cumulative PM2.5 exposure, the average WM volume was 6.23 cm3 (95% confidence interval, 3.72–8.74 cm3) lower in the whole brain and 4.47 cm3 (95% CI, 2.27–6.67 cm3) lower in frontal, parietal, and temporal WM. (Hippocampal volumes were not affected by pollution exposure.) The differences persisted after controlling for confounders including vascular white-matter changes and socioeconomic and health differences.

These changes were equivalent to 1 to 2 years of brain aging.