#AAIC21 – Air Pollution Linked to Dementia Risk in Older Women

Marta Figueiredo, PhD avatar

by Marta Figueiredo, PhD |

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Limiting air pollution may slow cognitive decline and lower the risk of dementia for older women, according to three analyses involving more than 2,000 women, ages 74 to 92, living across the U.S.

“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,” Claire Sexton, PhD, the director of Alzheimer’s Association’s scientific programs and outreach, said in a press release.

“What’s exciting is we’re now seeing data showing that improving air quality may actually reduce the risk of dementia,” Sexton said, adding that the data “demonstrate the importance of policies and action by federal and local governments, and businesses, that address reducing air pollutants.”

These findings were presented by Xinhui Wang, PhD, an assistant professor of research neurology at University of Southern California, at the Alzheimer’s Association International Conference 2021, taking place July 26–30 in-person in Denver, and virtually.

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The presentations were titled “Association of Air Quality Improvement with Slower Decline of Cognitive Function in Older Women,” “Heterogeneous Associations of Air Quality Improvement with Domain-Specific Cognitive Function in Older Women,” and “Association of Lower Dementia Risk with Improved Air Quality in Older Women.”

Increasing levels of air pollution and rising cases of dementia are worldwide public health crises. Previous studies have highlighted associations between poor air quality and the development of Alzheimer’s disease-related brain plaques.

Wang and colleagues evaluated whether older women living in U.S. locations with better air quality may have slower cognitive decline and be less likely to develop dementia than those in areas known for poorer quality.

They conducted three separate analyses of demographic, clinical, and location-specific air pollution data covering more than 2,000 women in those older age groups enrolled in the Women’s Health Initiative Memory Study-Epidemiology of Cognitive Health Outcomes, a National Institutes of Health-funded effort.

None of the women evaluated had dementia at the study’s beginning, and all completed annual cognitive function tests for up to 10 years, between 2008 and 2018.

Mathematical models were used to estimate annual exposures to air pollutants — such as extremely small, inhalable particles known as PM2.5, and nitrogen dioxide, an indicator of traffic-related pollutants — at the participants’ residential locations.

Air quality improvement was defined as a reduction in air pollution exposure between the 10-year period prior to enrollment and the most recent three-year period.

Results showed that, overall, air quality significantly improved over the 10 years before the study began.

Over a median of six years of follow-up, women’s cognitive function tended to decline with time, as expected. But those living in locations with greater reductions in air pollution showed slower declines, similar to those observed in women one to 1.5 years younger.

Particularly, improved air quality was associated with better episodic memory, working memory, and attention/executive function — cognitive domains with early decline in dementia before symptom onset. But it was not associate with better language skills.

Of note, episodic memory refers to consciously recalled memories of past experiences, and working memory to the brain’s ability to temporarily store and manipulate information while performing cognitive tasks.

Dementia was found in 398 women (nearly 20%) during the study. Notably, women living in areas with greater reductions in PM2.5 and nitrogen dioxide had a 14% to 26% lower risk of dementia, similar to risks seen in women two to three years younger.

These benefits were observed regardless of age, region, education level, and genetic and cardiovascular risk factors.

Results highlighted that better air quality, particularly reductions in fine particles and traffic-related pollutants, is linked to slower cognitive decline and a lower dementia risk in older women.

“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,” 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,” Wang added.

Similar, separate findings in French adults and in older U.S. adults were shared at the conference by Noemie Letellier, PhD, of the University of California, San Diego, and Christina Park, a doctoral student in the department of epidemiology at University of Washington.

“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,” Letellier said.