You are what you eat is a favorite maxim among those who strive for a healthy lifestyle. Now we're also learning that we may be what we breathe, especially as we grow older – and air pollution could harm your brain health.
This year, at least three studies have added to the long-held theory that air pollution may cause neurodegenerative disease. The studies underscore previous research that has drawn a link between the bad air we breathe and dangerous changes to our brains.
"There's always been a lot of interest in this," says Christian Camargo, M.D., a cognitive neurology specialist at the University of Miami Health System. "But we also have to be careful in drawing conclusions."
"We know there's a link, but we don't know if it's causal."
Dr. Camargo uses smoking and lung disease as an example. It took scientists years to prove a cause-and-effect between the two. But we're not there yet with air pollution and such brain diseases as Alzheimer's and Parkinson's. "It's a lot more complicated than a direct line," he explains. "There are many other factors to consider and control for."
The National Institute on Aging, National Institute of Neurological Disorders and Stroke, and the Centers for Disease Control and Prevention have publicly said that the causes of neurodegenerative disease are varied and likely due to a combination of genetic and environmental factors. In the meantime, studies continue to supply pieces of the jigsaw puzzle that is good brain health.
The most recent study, which appears in The Lancet Planetary Health journal, analyzes the link between fine particle pollution (referred to as PM2.5) and neurodegenerative disease. By sifting through hospital admissions for more than 63 million older U.S. adults, it found pollution was significantly associated with an increased risk of admissions for many neurological disorders, such as Alzheimer's and other dementias.
The study also revealed that white people, women, and urban populations were the most susceptible.
For example, the risk for first-time Parkinson's disease hospital admission was highest in the dense northeastern U.S. As for first-time Alzheimer's and related dementias, older adults in the Midwest faced the highest risk.
Does this mean that if you're a white woman living in New York City, you're more likely to be admitted to the hospital for Parkinson's in comparison to an African-American man living in a small town in Texas? It may be too soon for such predictions, Dr. Camargo says.
"There may be hidden variables that we don't know about," he says. "Did pollution cause it, or did it aggravate something that was already there?"
It's not just older people's brains that are affected by dirty air.
Another study, published earlier this year in the journal Environmental Research, found that the brain stems of both young adults and children exposed to air pollution have the markers of Alzheimer's, Parkinson's, and other neurological disorders. (Researchers analyzed autopsies of deceased young people from Mexico City, ranging in ages from 11 months to 40 years.) Researchers also found nanoparticles that can be traced to vehicles' internal combustion and braking systems.
In contrast, the control group of deceased young people who had lived in low pollution areas did not show these worrisome markers.
Another study showed that long-term air pollution exposure appears to inhibit cognitive performance among older adults in China. Subjects' performances were lower in tests that required recalling past knowledge, the ability to pay attention, as well as verbal and math tests.
This steady drumbeat of research should motivate us "to continue learning more about the environment and how it affects us," says Dr. Camargo. "We know that what you eat, what you drink, what you rub on your skin does exert influence on our health. What about what we breathe? What these studies tell us is that, hey, we need to look into this further."
The news is not all bad.
While this growing body of evidence sounds dire, we're not without options, says Dr. Camargo. Even before researchers can establish a causal link, we can make proactive, healthy lifestyle changes such as driving less and walking (or cycling) more. Planting trees and keeping lush greenery around us also helps. He points to the research of his colleague Scott Brown, Ph.D., a research assistant professor of public health sciences at the University of Miami Miller School of Medicine. His team found that living in neighborhoods with tree canopy and street-level vegetation has quantifiable benefits for our physical and mental health.
Residents of greener neighborhoods have a 29% lower risk for depression and an 18% decreased risk for Alzheimer's. And Medicare recipients living on "green" blocks also showed more significant improvements in obesity-related conditions such as diabetes, hypertension, and hyperlipidemia.
"I'm hoping [these studies] stimulate more thought and dialogue around this subject," Dr. Camargo says. "In the end, we have control over modifiable factors."
Ana Veciana-Suarez, Guest Columnist
Ana is a regular contributor to the University of Miami Health System. She is a renowned journalist and author who has worked at The Miami Herald, The Miami News, and The Palm Beach Post. Visit her website at anavecianasuarez.com or follow @AnaVeciana on Twitter.
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