Clearing pollution helps clear the fog of aging — and can reduce its risks

Over the past decade, a growing body of research has shown that air pollution damages the brain of older adults, contributing to cognitive decline and dementia. It is not clear whether improving air quality will benefit brain health.

Two studies published this year by researchers at six universities and the National Institute on Aging provide the first evidence of such benefits in an older population.

A report published in the Proceedings of the National Academy of Sciences found that the risk of dementia among women age 74 and older dropped significantly after a decade of reductions in two types of air pollution: nitrogen dioxide, a gaseous byproduct of motor vehicle emissions; , industrial sources, and natural events such as wildfires; and fine particulate matter, mixtures of very fine solids and liquids originating from similar sources.

A second report in PLOS Medicine, based on the same sample of more than 2,200 older women, found that lower levels of these pollutants were associated with slower rates of cognitive decline. In areas where air quality improvements were most significant, the rate of cognitive decline was delayed by up to 1.6 years, depending on the test.

Both studies are national in scope and account for other factors that may affect results, such as participants’ socioeconomic status, neighborhood characteristics, preexisting medical conditions, and lifestyle choices such as smoking.

What could explain their results? “We think that when air pollution levels are reduced, the brain is better able to recover from previous environmental insults,” said Xinhui Wang, assistant professor of research neurology at the University of Southern California Medical School. This hypothesis needs to be further tested in animal studies and with brain imaging, he suggests.

There are different theories about how air pollution affects the brain. Extremely small particles – at least 30 times larger than the largest particle in a human hair – can travel from the nasal cavity to the brain through the olfactory (smell) system, which puts the brain’s immune system on high alert. Or, pollutants can accumulate in the lungs, causing an inflammatory response that spreads and travels to the brain.

Also, pollutants can damage the cardiovascular system, which is essential for brain health. (Links between air pollution, stroke, and heart disease are well established.) Or tiny particles can cross the blood-brain barrier, causing direct damage. And oxidative stress can occur, releasing free radicals that damage cells and tissues.

Older adults are especially vulnerable to the harmful effects of air pollution because lung capacity declines and pollutants can exacerbate conditions such as respiratory illness and heart disease. Also, the effects of air pollution accumulate over time, and the longer people live, the greater the risk.

Yet recognition of the potential cognitive consequences of air pollution is relatively recent. After several smaller studies, the first national study showing a link between air pollution and cognition in a diverse sample of older men and women was published in 2014. It found that seniors living with high levels of fine particulate matter were more likely to experience Cognitive problems compared to people living in less polluted areas.

Another study, published a few years later, expanded on those findings, reporting that the cognitive effects of air pollution are increased among older adults living in disadvantaged areas where pollution levels are highest. The chronic stress that residents of these neighborhoods experience “may increase the rate at which neurons are damaged by toxic challenges,” the authors wrote.

Air pollution is only one of many factors influencing cognitive decline and dementia, the researchers agree, and such findings suggest correlation, not causation.

New research suggests that older adults’ cognition is affected even when exposures are below standards set by the Environmental Protection Agency. “With older adults, there is no safe level of air pollution,” says Jennifer Aylshire, associate professor of gerontology and sociology at the University of Southern California.

“It’s important to keep standards low for these pollutants,” said Antonella Janobetti, principal research scientist for Environmental Health at Harvard’s TH Chan School of Public Health. With colleagues, he has a National Institute on Aging grant to study how air pollution affects the risk of Alzheimer’s disease and related dementias among Medicare beneficiaries. In 2019, his work showed that higher levels of fine particles—a marker of disease progression—correlated with more hospitalizations among older adults with dementia.

Last year, in one of the largest US studies to date, a different set of researchers examined the link between long-term exposure to fine particulate matter and nitrogen dioxide among 12 million Medicare beneficiaries with a diagnosis of Alzheimer’s disease and other forms of dementia. Exposure to high levels of these pollutants has been shown to accelerate cognitive decline that was already relatively advanced, leading to an increase in diagnoses, the researchers concluded.

In addition to population-wide studies, about 20 scientific laboratories around the world are studying how air pollution contributes to dementia in animals. At USC, Caleb Finch, a professor who studies the neurobiology of aging, is co-principal investigator for a five-year, $11.5 million grant from the National Institute on Aging on how air pollution in urban areas informs and accelerates dementia risk. Aging of the brain

Among the questions that Finch said need to be addressed are: What areas of the brain appear to be most vulnerable to air pollution? When are people most at risk? How long does the damage last? Is recovery possible? And do lifestyle interventions such as diet and exercise help?

“The bottom line is that we now understand that Alzheimer’s disease is very sensitive to environmental influences, including air pollution,” Finch said.

Recognizing this, the Lancet’s Commission on Dementia Prevention, Intervention and Care added air pollution to a list of modifiable risk factors for dementia in 2020 and estimated that up to 40% of dementia cases worldwide could be prevented or delayed if these risk factors were addressed. .

For his part, Aylshire is optimistic that public policies can make a difference. From 2000 to 2019, he noted, average annual fine particulate matter pollution fell 43% nationally due to efforts to improve air quality. “I’m very optimistic that this effort will continue,” he told me.

What can older adults concerned about air pollution do on their own?

On very hot days, go for a walk in the morning rather than the afternoon when ozone levels are high, says Dr. Anthony Gerber, a pulmonologist at National Jewish Health, a medical center in Denver that specializes in respiratory diseases. Ozone, a toxic gas, is formed when various chemicals interact with sunlight and heat.

If you live in the western United States, where wildfires have become more common in spreading fine particles, “wear a KN95 mask” on days when fires are affecting air quality in your area, Gerber said. Also, if you can afford it, consider buying an air purifier for your home, he suggests, as fine particles can enter homes that aren’t sealed well.

To check air quality levels in your area, visit AirNow.gov, Ailshire recommends “If it’s a high-risk day, that might not be the day to go out and do heavy yard work,” he said.

But don’t stay inside all the time and don’t get overprotective. “It’s really important for older adults to get outside and exercise,” Gerber said. “We don’t want seniors to get sick because they’re breathing in a lot of particles, but we also don’t want them to become inactive and stuck at home.”

We’d love to hear from readers about questions you want answered, concerns you have about your care, and advice you need to deal with the health care system. Visit khn.org/columnists to submit your requests or tips.

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