Clearing pollution helps clear the fog of aging — and may reduce dementia risk

Over the past decade, a growing body of research has shown that air pollution damages the brains of older adults, contributing to cognitive decline and dementia. What remains unclear is whether improving air quality will benefit mental 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-long decline in two types of air pollution: nitrogen. Dioxide, a gaseous product of motor vehicle emissions, industrial sources, and natural events such as wildfires; and fine particles, mixtures of very small solids and liquids produced by similar sources.

A second report in PLOS Medicine, relying on the same sample of more than 2,200 older women, found that lower levels of these pollutants were associated with a slower rate of cognitive decline. In areas where the improvement in air quality was most notable, 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, pre-existing medical conditions, and lifestyle choices such as tobacco use. drinking

What could explain their findings? “We think that when air pollution levels are reduced, the brain is better able to recover,” said Xinhui Wang, assistant professor of research neurology at the University of Southern California’s medical school. This hypothesis needs to be further tested through animal studies and brain imaging.

There are several theories about how air pollution affects the brain. The tiny particles — at least 30 times the size of the largest particle in a human hair — can travel from the nasal cavities to the brain via the olfactory (smell) system, putting the brain’s immune system on high alert. . Or, the contamination can remain in the lungs, causing an inflammatory response that spreads and leads to the brain.

Also, pollution can damage the cardiovascular system, which is essential for mental health. (The links between air pollution, stroke, and heart disease are well established.) Or smaller 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 particularly vulnerable to the harmful effects of air pollution due to reduced lung capacity and increased pollution-induced conditions such as respiratory diseases and heart disease. Also, the effects of air pollution accumulate over time, and the longer people live, the greater the risks they may be exposed to.

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

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

Air pollution is just one of many factors that affect cognitive decline and dementia, researchers agree, and findings like these establish association, not causation.

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

“It’s important to keep reducing the quality of these pollutants,” said Antonella Zanobetti, 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 high levels of fine particles were linked to more hospitalizations in older adults with dementia — a marker of disease progression.

Last year, in the largest U.S. study ever, a different set of researchers looked at long-term exposure to fine particles and nitrogen dioxide among 12 million Medicare beneficiaries diagnosed with Alzheimer’s disease and other forms of dementia. Examined the relationship between The researchers concluded that exposure to high levels of these pollutants accelerates cognitive decline that was already relatively advanced, leading to increased prognosis.

In addition to larger population 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 to study How air pollution in urban areas informs and accelerates the risk of dementia. The brain is aging.

Among the questions Finch said need to be addressed are: What parts 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.

In recognition of this, the Lancet Commission on Dementia Prevention, Intervention, and Care in 2020 listed air pollution as a modifiable risk factor for dementia and estimated that it accounts for up to 40 percent of dementia cases worldwide. It can be prevented or delayed if these risk factors are addressed. .

For his part, Elshire is optimistic that public policies can make a difference. From 2000 to 2019, it noted, efforts to improve air quality led to a 43 percent reduction in average annual fine particulate pollution nationally. “I’m very optimistic that these efforts will continue,” he told me.

What can seniors 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 higher, said 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 U.S., where wildfires spewing fine particles have become more common, “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 properly sealed.

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

But don’t stay inside all the time and don’t overprotect yourself. “It’s really important for seniors to get outside and exercise,” Gerber said. Get stuck in.”

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