Jan. 3 (UPI) -- Long-term improvement in air quality lowers the risk for dementia in older women, a study published Monday by the Proceedings of the National Academy of Sciences found.
Large reductions in air pollution reduce the likelihood women ages 74 to 92 years will develop dementia, or memory loss and declines in brain function, as they age by up to 20%, the data showed.
The decline in dementia risk for women in this group associated with boosts in air quality was equivalent to taking nearly 2 1/2 years off of their age, the researchers said.
"Our findings strengthen the evidence that high levels of air pollution can harm our brain, and that reducing the exposure may promote healthier brain aging in older women," study co-author Diana Younan told UPI in an email.
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"These toxic pollutants cause inflammation in the lungs and blood that may be harmful to the aging brains, resulting in altered brain function," said Younan, an observational research manager at drug-maker Amgen, who was at the University of Southern California at the time of the study.
The findings are based on an analysis of the effects of exposure to high levels of fine particulate matter, or PM2.5, and nitrogen dioxide in women from across the United States, Younan and her colleagues said.
PM2.5 is a mixture of microscopic solid substances and liquid droplets found in the air, including dust, dirt, soot and smoke, according to the Environmental Protection Agency.
Nitrogen dioxide is found in exhaust from motor vehicles, as well as emissions from the combustion of coal, oil or natural gas and various industrial sources, the agency says.
An estimated 90% of the global population lives in regions with PM2.5 and nitrogen dioxide levels above the thresholds for human health established by the World Health Organization, the international body estimates.
In a study published in November, researchers in China found that exposure to high levels of air pollution increases a person's risk for depression and adversely affects brain function.
A separate study published in August indicated that small increase in exposure to fine particle air pollution in Seattle increase local residents' risk for dementia by 16%.
In addition, fine particulate matter such as PM2.5 has been linked with up to 4 million early deaths worldwide annually and has been described as "the greatest threat to human health."
For this study, Younan and her colleagues assessed the cognitive, or brain, function of 2,239 women in the United States annually between 2008 and 2018, using standard tests.
None of the women in the study had been diagnosed with dementia at the start of the research, Younan and her colleagues said.
Participants' performance on the tests was cross-referenced against changes in yearly average concentrations of outdoor air pollution for the regions in which they lived over a 15-year period, the researchers said.
Of the participants, 398, or 18%, developed dementia over the course of the study period, the researchers said.
Participants residing in locations that experienced larger reductions in PM2.5 and nitrogen dioxide had a lower risk for dementia than those living in regions that saw less air quality improvement, the data showed.
Those living in areas that saw PM2.5 and nitrogen dioxide levels in the air reduced by roughly 20% had a 20% lower risk for dementia, according to the researchers.
"The health benefits seen in our study were a result of decreasing levels of both PM2.5 and nitrogen dioxide across the U.S., which were likely due to national policies and strategies aimed at regulating pollution," Younan said.
"We think that continuing these regulatory efforts are important for improving brain health of older women," she said.
