Exposure to air pollution has been known to affect respiratory diseases, lung function and cardiac health, but a new study led by Keck School of Medicine of the University of Southern California (USC) researchers shows for the first time that it may also have a negative impact on how the brain’s white matter ages.

The research indicates that older women who lived in geographic locations with higher levels of fine particulate matter in ambient air had significantly smaller white matter volumes across a wide range of brain areas.

Fine particulate matter is smaller than 2.5 micrometers and is known as PM2.5, a form of pollution that easily enters the lungs and possibly the bloodstream. White matter connects brain regions and determines how information is processed in the brain.

“Investigating the impact of air pollution on the human brain is a new area of environmental neurosciences,” said Jiu-Chiuan Chen, MD, MPH, ScD, associate professor of preventive medicine at the Keck School of Medicine and lead author of the research. “Our study provides convincing evidence that several parts of the aging brain, especially the white matter, are an important target of neurotoxic effects induced by long-term exposure to fine particles in the air.”

The study found that older women ages 71 – 89 who had lived in places with greater PM2.5 exposures had significantly smaller volumes of white matter, and that this could not be explained by the geographic region where they lived, their race or ethnic background, socioeconomic status, lifestyle, or medical conditions that may also influence brain volumes.

The researchers performed brain magnetic resonance imaging (MRI) scans of 1,403 women who are part of the Women’s Health Initiative Memory Study (WHIMS), a nationwide study based at Wake Forest Baptist Medical Center in Winston-Salem, N.C. The researchers also used residential histories and air monitoring data to estimate the participants’ exposure to air pollution in the previous six to seven years.

This is the first study to differentiate between white and gray matter while examining the neurotoxic effects of PM2.5 on brain volumes of older people. The USC-led research may be the largest neuroimaging study conducted in community-dwelling elderly persons to examine the association between long-term PM2.5 exposures and volumes of gray matter and white matter in the brain.

White matter contains nerve fibers and connects brain regions with each other by traveling deep within and passing nerve signals throughout the brain. Gray matter is primarily composed of neuronal cell bodies, dendrites, glial cells and capillaries. The study did not find impacts from exposure to air pollution in participants’ gray matter.

The WHIMS study began in 1996 at Wake Forest Baptist Medical Center for the purpose of studying how postmenopausal hormone treatment affects cognitive impairment and brain aging.

The research appears in the June 15, 2015 issue of the Annals of Neurology. Co-authors include Xinhui Wang, MS, and Helena Chui, MD of the Keck School of Medicine of USC; John McArdle, PhD of the USC Dornsife College of Letters, Arts and Sciences; Gregory Wellenius, ScD of Brown University; Mark Serre, PhD of the University of North Carolina; Ira Driscoll, PhD of the University of Wisconsin; Ramon Casanova, PhD and Mark Espeland, PhD of Wake Forest Baptist Medical Center; and JoAnn Manson, MD, Dr PH of Harvard Medical School.

The collaborative study was funded in part by the National Institutes of Health grant R01AG033078 and by the Rosenblith Award from the Health Effects Institute, an organization jointly funded by the United States Environmental Protection Agency and certain auto and engine manufacturers. The work was also supported by the Southern California Environmental Health Sciences Center (5P30ES007048). The research was also supported by the National Heart, Lung, and Blood Institute, National Institute on Aging, National Institutes of Health, U.S. Department of Health and Human Services through contracts and by Wyeth Pharmaceuticals, Inc, St. Davids, Pa., and Wake Forest Baptist Medical Center, which funds the Women’s Health Initiative Program and its memory study.

by Leslie Ridgeway

Article cited:
Chen, J.C., Wang, X., Wellenius. G.A., Serre, M.L., Driscoll, I., Casanova, R. McArdle, J.J., Manson, J.E., Chui, H.C., Espeland, M.A.. Ambient Air Pollution and Neurotoxicity on Brain Structure: Evidence from Women’s Health Initiative Memory Study. Annals of Neurology June 15, 2015. doi: 10.1002/ana.24460. [Epub ahead of print]. PMID: 26075655