A possible link between dementia and air pollution

A report published in the Proceedings of the National Academy of Sciences found that the risk of dementia in women aged 74 and older has fallen significantly after decades of reductions in two types of air pollution: nitrogen dioxide, a gaseous byproduct of emissions from engine vehicles, industrial sources, and natural phenomena like forest fires; and particulate matter, a mixture of extremely small solids and liquids derived 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 cognitive decline. In areas where air quality improved the most, cognitive decline was delayed by up to 1.6 years, depending on the test.

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Both studies are national in nature and take into account other factors that could affect the results, such as: B. the socioeconomic status of the participants, characteristics of the neighborhood, pre-existing medical conditions and lifestyle choices such as smoking.

What could explain their results?

“We believe that when air pollution is reduced, the brain is better able to recover from previous environmental aggressions,” said Xinhui Wang, assistant professor of research neurology at the University of Southern California School of Medicine. The hypothesis needs to be further investigated in animal studies and through brain imaging, she suggested.

There are several theories about how air pollution affects the brain. Extremely small particles – a human hair is at least 30 times the size of the largest particle – could travel from the nasal cavities to the brain via the olfactory (smelling) system, putting the brain’s immune system on high alert. Or pollutants can lodge in the lungs and trigger an inflammatory response that spreads 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 and cause direct harm. And it can lead to oxidative stress, which releases 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 the potential of pollutants to aggravate conditions such as respiratory disease and heart disease. Also, the effects of air pollution accumulate over time, and the longer people live, the more risks they can take.

However, the realization of the potential cognitive consequences of air pollution is relatively new.

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. She found that seniors living in areas with high particulate matter pollution were more likely to have cognitive problems than those living in less polluted areas.

Another study published a few years later expanded on these findings by reporting that the cognitive effects of air pollution are amplified in older adults living in disadvantaged neighborhoods where pollution levels tend to be highest. The chronic stress experienced by residents of these neighborhoods “can increase the rate at which neurons are damaged by toxic exposures,” the authors write.

Air pollution is just one of many factors that influence cognitive decline and dementia, researchers said, and findings of this type establish association, not causation.

Is my memory working or is it just normal aging?

Recent research suggests that older adults’ cognition is impaired even at exposures below the standards set by the Environmental Protection Agency.

“With older adults, there really is no level at which air pollution is safe,” said Jennifer Ailshire, associate professor of gerontology and sociology at the University of Southern California.

“It’s important to continue lowering the standards for these pollutants,” said Antonella Zanobetti, senior research scientist in environmental health at Harvard’s TH Chan School of Public Health. She, along with colleagues, received a grant from the National Institute on Aging to study how air pollution affects the risk of Alzheimer’s disease and related dementia in Medicare beneficiaries. In 2019, her work showed that higher particulate matter levels are associated with more hospital admissions in older adults with dementia — a marker of disease progression.

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

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

Among the questions that need to be addressed, Finch said, are: Which areas of the brain appear to be most vulnerable to airborne pollutants? When are people most at risk? How long does the damage last? Is recovery possible? And do lifestyle interventions like diet and exercise help?

“The main point is that we now recognize that Alzheimer’s disease is very sensitive to environmental influences, including air pollution,” Finch said.

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

For her part, Ailshire is optimistic that public policy can make a difference. From 2000 to 2019, average annual particulate matter pollution fell 43 percent nationwide due to efforts to improve air quality. “I am very confident that this effort will continue,” she told me.

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What can older adults concerned about air pollution do for themselves?

On hot days, go for walks in the morning instead of in the afternoon when ozone levels are higher, said Anthony Gerber, a pulmonologist at National Jewish Health, a Denver medical center specializing 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 that spread particulate matter have become more common, “wear a KN95 mask” on days when fires are affecting air quality in your area, Gerber said.

If you can afford it, you should also buy air purifiers for your home, he advised, noting that particulate matter can get into homes that aren’t well sealed.

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

But don’t stay indoors all the time and become overly self-protective.

“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 particulate matter, but we don’t want them to become inactive and stuck at home either.”

This item was produced by Kaiser Health News, a program of the Kaiser Family Foundation, a donated nonprofit organization that provides information to the nation on health issues.