Brain Fog

Several recent studies suggest that certain kinds of air pollution may affect cognitive function.

By Dawn Fallik

It’s well established that air pollution affects respiratory function, exacerbating conditions such as asthma and heart disease. What is less well known or studied is how poor air quality affects the brain. That question nagged at Jennifer Ailshire, PhD, an assistant professor of gerontology at the University of Southern California (USC), after she moved to Los Angeles from Ann Arbor, MI.

“On days when there is a lot of smog and haze, the mountains are hidden,” says Dr. Ailshire, who works with the Center on Biodemography and Population Health at USC/University of California, Los Angeles.


To find out how smoggy, hazy days affect vulnerable populations, particularly older people who live in highly congested areas, Dr. Ailshire analyzed data from the University of Michigan Health and Retirement Study of nearly 20,000 men and women over the age of 50. The study included cognitive tests as well as memorizing and repeating words. She then looked at the air quality in the places where the subjects lived, as measured by the Environmental Protection Agency’s (EPA) Air Quality System, to see if there was a correlation between low scores and poor air quality.

The results, which were published in the American Journal of Epidemiology in June 2014, revealed that people over the age of 50 who lived in areas with higher amounts of fine particulate matter—the kind usually found in smoke or haze—performed almost twice as poorly on the cognitive tests as those who lived in less polluted areas.

Dr. Ailshire cautions that while her study shows an association between pollution and cognitive decline, it does not prove that pollution causes the decline. Those with existing health problems are more vulnerable to pollution and more likely to experience cognitive decline associated with exposure.


In another study, published in the Annals of Neurology in June 2015, researchers at the Keck School of Medicine at USC looked at the magnetic resonance imaging scans of more than 1,400 women between the ages of 71 and 89, who are part of the national Women’s Health Initiative Memory Study. The researchers also examined residential history and air-monitoring data to determine the participants’ exposure to air pollution. Women who lived in areas with a higher volume of fine particle pollution had significantly smaller volumes of white matter, which comprises nerve fibers that connect to each other so that nerves can communicate and process information. The researchers concluded that white matter loss in these women was equal to one to two years of brain aging.

Once inhaled, air pollution particles can travel through the circulatory system and damage organs, including the brain, says Melinda C. Power, ScD, an assistant professor of epidemiology at the George Washington University in Washington, DC. “The idea that particulate matter can get into the brain is something toxicologists have reported, but it’s a relatively recent finding,” she says.


The EPA has been reducing the allowable levels of fine particulate matter since it started regulating and measuring them in the mid-1990s. In 2012, the agency tightened its air pollution standards and placed air quality monitors near high-traffic roadways. But because air pollution is a mixture of different components, including road dust, car emissions, and soil, it’s hard to know which pollutants are the most problematic.
Consider these steps to limit your exposure.

Check online. Visit the EPA’s website at to check your area’s air quality. At the top of the page, type in your zip code to find the air quality level and the forecast in that area.

Pressure politicians. If you notice that your community is frequently outside the “good” zone, contact the local EPA office as well as your local politicians to see who the biggest polluters are in your area and what the office is doing to address air quality standards. “Lowering the levels of fine particulate matter, could have a big effect on people’s health,” says Dr. Power.

Rethink outdoor exercise. When the air quality is poor, the EPA suggests limiting outdoor exercise, choosing less strenuous activities, avoiding activity near busy roads, and exercising indoors. “I check the air quality reports, and I change some of my outdoor exercise habits based on that,” says Dr. Ailshire.

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