Several researchers said avoiding exposure to pollution could reduce cognitive decline by up to 26 percent.

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Eating healthy meals and getting ample exercise are two ways to boost brain health over the years. But according to a new study, there's another key part of this equation: Improved air quality can positively impact the brain and prevent dementia, too. "We've known for some time that air pollution is bad for our brains and overall health, including a connection to amyloid buildup in the brain," said Claire Sexton, DPhil, the Alzheimer's Association director of scientific programs and outreach. "But what's exciting is we're now seeing data showing that improving air quality may actually reduce the risk of dementia. These data demonstrate the importance of policies and action by federal and local governments and businesses that address reducing air pollutants."

smoke coming out of chimney stack
Credit: Eric Yang / Getty Images

In partnership with the National Institutes of Health-funded Women's Health Initiative Memory Study-Epidemiology of Cognitive Health Outcomes (WHIMS-ECHO), Xinhui Wang, Ph.D., the assistant professor of research neurology at University of Southern California, and her fellow colleagues studied women in the United States between the ages of 74 and 92, who lived without dementia. The group completed cognitive function tests from 2008 to 2018, during which the researchers tracked the pollution levels around their homes. While the scientists found that air quality generally improved over the course of the 10-year timespan and the participants' cognitive tests declined six years into follow-up examinations, the senior women who lived in areas with a larger reduction of pollution decreased their dementia risks by up to 26 percent.

"Our findings are important because they strengthen the evidence that high levels of outdoor air pollution in later life harm our brains, and also provide new evidence that by improving air quality, we may be able to significantly reduce risk of cognitive decline and dementia," Dr. Wang said. "The possible benefits found in our studies extended across a variety of cognitive abilities, suggesting a positive impact on multiple underlying brain regions."

A similar study by Noemie Letellier, Ph.D., a postdoctoral scholar at the University of California, San Diego, studied over 7,000 people over the age of 65 between 1990 to 2000. During this period, the researchers looked into the reduction of PM2.5 concentration, a marker of air quality, and noticed that the risks of dementia decreased by 15 percent and Alzheimer's risks lessened by 17 percent based on every microgram of gaseous pollutant per cubic meter of air (µg/m3) decrease in PM2.5. "These data, for the first time, highlight the beneficial effects of reduced air pollution on the incidence of dementia in older adults," Dr. Letellier said. "The findings have important implications to reinforce air quality standards to promote healthy aging. In the context of climate change, massive urbanization, and worldwide population aging, it is crucial to accurately evaluate the influence of air pollution change on incident dementia to identify and recommend effective prevention strategies."

Another study by Christina Park, a doctoral student in the Department of Epidemiology at University of Washington, examined how air pollutants with fine particulate matter (PM2.5) and larger particles (PM10) and nitrogen dioxide (NO2) could impact 3,000 people. As a result, they found that those who were in the study for over eight years had direct exposure to the pollutants and Aβ1-40 (one of the major protein components of brain plaques) in their blood. "Our findings suggest that air pollution may be an important factor in the development of dementia," Park said. "Many other factors that impact dementia are not changeable, but reductions in exposure to air pollution may be associated with a lower risk of dementia. More research is needed."

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