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Pollutants in the air -- fine particulates that are 30 times smaller than the width of a strand of hair -- may be damaging older women's brains.
"Fine-particle pollution is kind of like a cocktail. There are a lot of different things involved," said study lead author Diana Younan, senior research associate at the University of Southern California. "It could come from, of course, traffic, but it could also come from fires, from dust, from power plants, from agricultural work."
The researchers studied more than 700 women in their 70s and 80s who did not already have dementia, using data from the Women's Health Initiative Memory Study. The women had brain scans at the beginning of the study and about five years later. They also provided medical histories and answered a range of demographic and health questions.
Older women who were exposed to higher levels of tiny particulates of air pollution had a greater amount of brain shrinkage over five years, according to the study.
"It could be that the pollution itself is getting into the brain. … These are tiny, tiny particles. They're 30 times smaller than [the width of] a strand of hair. You can't see them, but we might be actually inhaling them through the nose and they're getting into the brain and destroying connections in the brain or the neurons in the brain," Younan suggested.
"It could also be that it's having a secondary reaction where we're inhaling them into our lungs and then that's triggering an inflammatory response," she added.
Dr. Thomas Wisniewski is director of the NYU Langone Alzheimer's Disease Research Center.
"It's clear that this is an important environmental risk factor and it's another good reason for trying to clean up the environment," he said.
"Dementia is the most expensive thing in health care now globally, as the global population ages. If you have an identified risk mitigation factor, then it really behooves society to address the problem to help reduce this health care crisis," said Wisniewski, who wasn't involved with the study.
Younan and her colleagues relied on a machine learning tool trained to identify patterns of brain shrinkage specific to Alzheimer's risk. They used the women's addresses to determine average exposure to pollution in the three years prior to the initial scan. And they divided participants into four groups according to their levels of exposure to fine-particle pollutants.
Scores ranged from 0 to 1, with higher scores showing more brain changes. Overall, the women's scores changed from .28 to .44 after five years. For each additional 3 micrograms of fine-particle pollution per cubic meter of air, researchers found an average score increase of .03, showing a greater extent of brain shrinkage. This was equivalent to a 24% increased risk of Alzheimer's disease.
The study can't prove a direct cause-and-effect relationship. Still, people who live in metropolitan areas may be more at risk, Younan said.
She also noted that some of the exposure levels included in the research were below current U.S. Environmental Protection Agency standards for what's safe.
"That could have some public health implications and maybe even suggest that the current levels might still be too high," Younan said.
You can help mitigate some of the risks by paying attention to air quality numbers, working out indoors when the air quality is bad, keeping car vents closed and filtering out air pollution through air conditioning systems at home, Younan said.
Wisniewski said you also can influence your own brain health through healthy habits. This includes regular exercise and a Mediterranean diet full of grains, nuts, fruits and vegetables. Also important are good sleep, activities that keep the brain active and treating any blood pressure, cholesterol or glucose issues.
"For the common, late-onset form of Alzheimer's disease, lifestyle and environmental things play a very substantial role. These factors have an interplay with one's genetic background, but the lifestyle things can make a key effect as to what age you present with symptoms," Wisniewski said.
The findings were published Nov. 18 in the online issue of Neurology.
The Alzheimer's Association offers more on reducing your risks for dementia.
SOURCES: Diana Younan, PhD, MPH, senior research associate, University of Southern California, Los Angeles; Thomas Wisniewski, MD, professor, neurology, pathology and psychiatry, New York University School of Medicine, and director, NYU Langone Alzheimer's Disease Research Center, New York City; Neurology, Nov. 18, 2020, online
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