air pollution brain health, air quality, air pollutants

Pollution and Dementia: Scientists Link Air Quality and Brain Health

By Nicholas Chan | July 26th, 2021

New research suggests that reducing harmful air pollutants can decrease dementia risk by up to 26 percent.

Exposure to air pollution is widely known as a risk factor for health conditions such as lung cancer, heart disease and respiratory infections, but scientists have also turned their attention to its potential consequences for brain health. 

Multiple studies presented at the Alzheimer’s Association International Conference 2021 suggest that reducing air pollutants can help lower the likelihood of dementia, offering a blueprint for improving cognitive health on an individual basis, but also on a widespread scale.

Past findings have indicated that poor air quality may be a significant risk factor for dementia. One study previously found that people living near major roads or highways have higher chances of developing dementia, Parkinson’s, multiple sclerosis and Alzheimer’s. And after reviewing past scientific evidence, researchers recently identified air pollution as one of 12 controllable risk factors for dementia, accounting for two percent of dementia cases worldwide. 

Now, researchers are diving deeper, exploring the extent to which combating air pollution may benefit brain health: New research has zeroed in on specific air pollutants known as PM2.5 and NO2 levels, finding that reductions in these types of pollutants are associated with a decrease in dementia risk by 14 percent and 26 percent, respectively.

According to Xinhui Wang, a scientist in the team behind this research and an assistant professor of research neurology at the University of Southern California, her group’s findings not only reinforce earlier findings that air pollution is detrimental to brain health, but take those findings a step further, revealing that improving air quality may help preserve a number of brain functions. 

“The possible benefits found in our studies extended across a variety of cognitive abilities, suggesting a positive impact on multiple underlying brain regions,” Wang said in a news release.

Wang and colleagues probed the link between improved air quality, cognition and dementia risk by examining data of more than 2,000 women between the ages of 74 to 92. The team estimated air pollution levels at participants’ areas of residence and analyzed their cognitive performance year over year. 

The scientists observed that PM2.5 and NO2 levels decreased over the 10-year period before participants were enrolled in the study. During the median of 6.2 years of follow-up, participants’ cognition declined, but those living in places with greater measures of air quality improvement experienced slower decline in cognitive function.  

With the exception of language skills, people residing in areas with greater improvements in PM2.5 and NO2 levels had better performances in episodic memory (recollection of personal experiences), working memory (ability to retain and manipulate information in brief intervals), and attention or executive function (planning, organizing, setting goals, etcetera). 

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Another team of researchers, who studied more than 7,000 participants with the median age of 73, provides further evidence of the link between air quality improvement and reduced dementia risk. The scientists found that the reduction in PM2.5 levels over 10 years was associated with a 15 percent and 17 percent decrease in dementia and Alzheimer’s risk, respectively. 

“The findings have important implications to reinforce air quality standards to promote healthy aging,” Noemie Letellier, a researcher in the study and a postdoctoral scholar at University of California San Diego, said in a news release.

“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.

Scientists have proposed possible reasons as to why the association between air pollution and dementia exists. Experts say air pollutants may alter the body’s immune response and lead to brain inflammation, biological mechanisms that have been implicated in Alzheimer’s and related dementias.

According to researchers, long-term inflammation may in turn lead to the build-up of beta-amyloid proteins, a telltale sign of Alzheimer’s. Research presented at the Alzheimer’s Association International Conference, along with past studies, has shown that exposure to harmful air pollutants is indeed associated with increased levels of beta-amyloid. 

But researchers emphasize it is still too big of a leap to conclude that high levels of air pollution can directly cause dementia: As the adage goes, correlation does not imply causation. Plus, there may still be unknown factors that explain the link between air pollution and dementia. 

Meanwhile, experts say there’s a lot that people can do in their daily lives to reduce greenhouse gas emissions, whether it’s buying local foods, reusing and recycling materials or adopting dietary changes. 

Researchers also urge policy makers to increase people’s access to green spaces, to reduce traffic pollution, and to hasten their efforts in improving air quality — strategies that could play an important role in maintaining brain health. 

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