For years, the two patients had come to the Penn Memory Center at the University of Pennsylvania, where doctors and researchers follow people with cognitive impairment as they age, as well as a group with normal cognition.

Both patients, a man and a woman, had agreed to donate their brains after they died for further research. “An amazing gift,” said Edward Lee, the neuropathologist who directs the brain bank at the university’s Perelman School of Medicine. “They were both very dedicated to helping us understand Alzheimer’s disease.”

The man, who died at 83 with dementia, had lived in the Center City neighborhood of Philadelphia with hired caregivers. The autopsy showed large amounts of amyloid plaques and tau tangles, the proteins associated with Alzheimer’s disease, spreading through his brain.

Researchers also found infarcts, small spots of damaged tissue, indicating that he had suffered several strokes.

By contrast, the woman, who was 84 when she died of brain cancer, “had barely any Alzheimer’s pathology,” Lee said. “We had tested her year after year, and she had no cognitive issues at all.”

The man had lived a few blocks from Interstate 676, which slices through downtown Philadelphia. The woman had lived a few miles away in the suburb of Gladwyne, Pennsylvania, surrounded by woods and a country club.

The amount of air pollution she was exposed to — specifically, the level of fine particulate matter called PM2.5 — was less than half that of his exposure. Was it a coincidence that he had developed severe Alzheimer’s while she had remained cognitively normal?

With increasing evidence that chronic exposure to PM2.5, a neurotoxin, not only damages lungs and hearts but is also associated with dementia, probably not.

“The quality of the air you live in affects your cognition,” said Lee, the senior author of a recent article in JAMA Neurology, one of several large studies in the past few months to demonstrate an association between PM2.5 and dementia.

Scientists have been tracking the connection for at least a decade. In 2020, the influential Lancet Commission added air pollution to its list of modifiable risk factors for dementia, along with common problems like hearing loss, diabetes, smoking, and high blood pressure.

Yet such findings are emerging when the federal government is dismantling efforts by previous administrations to continue reducing air pollution by shifting from fossil fuels to renewable energy sources.

“‘Drill, baby, drill’ is totally the wrong approach,” said John Balmes, a spokesperson for the American Lung Association who researches the effects of air pollution on health at the University of California-San Francisco.

“All these actions are going to decrease air quality and lead to increasing mortality and illness, dementia being one of those outcomes,” Balmes said, referring to recent environmental moves by the White House.

Many factors contribute to dementia, of course. But the role of particulates — microscopic solids or droplets in the air — is drawing closer scrutiny.

Particulates arise from many sources: emissions from power plants and home heating, factory fumes, motor vehicle exhaust, and, increasingly, wildfire smoke.

Of the several particulate sizes, PM2.5 “seems to be the most damaging to human health,” Lee said, because it is among the smallest. Easily inhaled, the particles enter the bloodstream and circulate through the body; they can also travel directly from the nose to the brain.

The research at the University of Pennsylvania, the largest autopsy study to date of people with dementia, included more than 600 brains donated over two decades.

Previous research on pollution and dementia mostly relied on epidemiological studies to establish an association. Now, “we’re linking what we actually see in the brain with exposure to pollutants,” Lee said, adding, “We’re able to do a deeper dive.”

The study participants had undergone years of cognitive testing at Penn Memory. With an environmental database, the researchers were able to calculate their PM2.5 exposure based on their home addresses.

The scientists also devised a matrix to measure how severely Alzheimer’s and other dementias had damaged donors’ brains.

Lee’s team concluded that “the higher the exposure to PM2.5, the greater the extent of Alzheimer’s disease,” he said. The odds of more severe Alzheimer’s pathology at autopsy were almost 20% greater among donors who had lived where PM2.5 levels were high.

Another research team recently reported a connection between PM2.5 exposure and Lewy body dementia, which includes dementia related to Parkinson’s disease. Generally considered the second most common type after Alzheimer’s, Lewy body accounts for an estimated 5% to 15% of dementia cases.

In what the researchers believe is the largest epidemiological study to date of pollution and dementia, they analyzed records from more than 56 million beneficiaries with traditional Medicare from 2000 to 2014, comparing their initial hospitalizations for neurodegenerative diseases with their exposure to PM2.5 by ZIP codes.

“Chronic PM2.5 exposure was linked to hospitalization for Lewy body dementia,” said Xiao Wu, an author of the study and a biostatistician at the Mailman School of Public Health at Columbia University.

After controlling for socioeconomic and other differences, the researchers found that the rate of Lewy body hospitalizations was 12% higher in U.S. counties with the worst concentrations of PM2.5 than in those with the lowest.

To help verify their findings, the researchers nasally administered PM2.5 to laboratory mice, which after 10 months showed “clear dementia-like deficits,” senior author Xiaobo Mao, a neuroscientist at the Johns Hopkins School of Medicine, wrote in an email.

The mice got lost in mazes that they had previously dashed through. They had earlier built nests quickly and compactly; now their efforts were sloppy, disorganized. At autopsy, Mao said, their brains had atrophied and contained accumulations of the protein associated with Lewy bodies in human brains, called alpha-synuclein.

A third analysis, published this summer in The Lancet, included 32 studies conducted in Europe, North America, Asia, and Australia. It also found “a dementia diagnosis to be significantly associated with long-term exposure to PM2.5” and to certain other pollutants.

Whether so-called ambient air pollution — the outdoor kind — increases dementia because of inflammation or other physiological causes awaits the next round of research.

Although air pollution has declined in the United States over two decades, scientists are calling for still stronger policies to promote cleaner air. “People argue that air quality is expensive,” Lee said. “So is dementia care.”

President Donald Trump, however, reentered office vowing to increase the extraction and use of fossil fuels and to block the transition to renewable energy. His administration has rescinded tax incentives for solar installations and electric vehicles, Balmes noted, adding, “They’re encouraging continuing to burn coal for power generation.”

The administration has halted new offshore wind farms, announced oil and gas drilling in the Arctic National Wildlife Refuge in Alaska, and moved to stop California’s plan to transition to electric cars by 2035. (The state has challenged that action in court.)

“If policy goes in the opposite direction, with more air pollution, that’s a big health risk for older adults,” Wu said.

Last year, under the Biden administration, the Environmental Protection Agency set tougher annual standards for PM2.5, noting that “the available scientific evidence and technical information indicate that the current standards may not be adequate to protect public health and welfare, as required by the Clean Air Act.”

In March, the EPA’s new chairman announced that the agency would be “revisiting” those stricter standards.

The New Old Age is produced through a partnership with The New York Times.

KFF Health News is a national newsroom that produces in-depth journalism about health issues and is one of the core operating programs at KFF—an independent source of health policy research, polling, and journalism. Learn more about KFF.

This article first appeared on KFF Health News and is republished here under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

KFF Health News Peggy Girshman reporting fellow Jackie Fortiér joined a boat tour to spotlight a review of microbes in the Anacostia River, a step toward making the river healthier and swimmable. The story was featured on WAMU’s “Health Hub” on Feb. 26.

On a bright October day, high schoolers from Francis L. Cardozo Education Campus piled into a boat on the Anacostia River in Washington, D.C. Most had never been on the water before.

Their guide, Trey Sherard of the Anacostia Riverkeeper, started the tour with a well-rehearsed safety talk. The nonprofit advocates for the protection of the river.

A boy with tousled black hair casually dipped his fingers in the water.

“Don’t touch it!” Sherard yelled.

Why was Sherard being so stern? Was it dangerously cold? Were there biting fish?

Because of the sewage.

“We get less sewage than we used to. Sewage is a code word for what?” Sherard asked the teenagers.

“Poop!” one student piped up.

“Human poop,” Sherard said. “Notice I didn’t say we get none. I said we get what? Less.”

Tours like this are designed to get young people interested in the river’s ecology, but it’s a fine line to tread — interacting with the water can make people sick. Because of the health risks, swimming hasn’t been legal in the Anacostia for more than half a century. The polluted water can cause gastrointestinal and respiratory illnesses, as well as eye, nose, and skin infections.

The river is the cleanest it’s been in years, according to environmental experts, but they still advise you not to take a dip in the Anacostia — not yet, at least.

About 40 million people in the U.S. live in a community with a combined sewer system, where wastewater and stormwater flow through the same pipes. When pipe capacities are reached after heavy rains, the overflow sends raw wastewater into the rivers instead of to a treatment plant.

Federal regulations, including sections of the Clean Water Act, require municipalities such as Washington to reduce at least 85% of this pollution or face steep fines.

To achieve compliance, Washington launched a $2.6 billion infrastructure project in 2011. DC Water’s Clean Rivers Project will eventually build multiple miles-long underground storage basins to capture stormwater and wastewater and pump it to treatment plants once heavy rains have subsided.

The Anacostia tunnel is the first of these storage basins to be completed. It can collect 190 million gallons of bacteria-laden wastewater for later treatment, said Moussa Wone, vice president of the Clean Rivers Project.

Climate change is causing more intense rainstorms in Washington, so even after construction is complete in 2030, Wone said, untreated stormwater will be discharged into the river, though much less frequently.

“On the Anacostia, we’re going to be reducing the frequency of overflows from 82 to two in an average year,” Wone said.

But while the Anacostia sewershed covers 176 square miles, he noted, only 17% is in Washington.

“The other 83% is outside the district,” Wone said. “We can do our part, but everybody else has to do their part also.”

Upstream in Maryland’s Montgomery and Prince George’s counties, miles of sewer lines are in the process of being upgraded to divert raw sewage to a treatment plant instead of the river.

The data shows that poop is a problem for river health — but knowing what kind of poop it is matters. Scientists monitor E. coli to indicate the presence of feces in river water, but since the bacteria live in the guts of most warm-blooded animals, the source is difficult to determine.

“Is it human feces? Or is it deer? Is it gulls’? Is it dogs’?” said Amy Sapkota, a professor of environmental and occupational health at the University of Maryland.

Bacterial levels can fluctuate across the river even without rainstorms. An Anacostia Riverkeeper report found that in 2023 just three of nine sites sampled along the Washington portion of the watershed had consistently low E. coli levels throughout the summer season.

Sapkota is heading a new bacterial monitoring program measuring the amount of E. coli that different animal species deposit along the river.

The team uses microbial source tracking to analyze samples of river water taken from different locations each month by volunteers. The molecular approach enables scientists to target specific gene sequences associated with fecal bacteria and determine whether the bacteria come from humans or wildlife. Microbial source tracking also measures fecal pollution levels by source.

“We can quantify the levels of different bacterial targets that may be coming from a human fecal source or an animal fecal source,” Sapkota said.

Her team expects to have preliminary results this year.

The health risk to humans from river water will never be zero, Sapkota said, but based on her team’s research, smart city planning and retooled infrastructure could lessen the level of harmful bacteria in the water.

“Let’s say that we’re finding that actually there’s a lot of deer fecal signatures in our results,” Sapkota said. “Maybe this points to the fact that we need more green buffers along the river that can help prevent fecal contaminants from wildlife from entering the river during stormwater events.”

Washington is hoping to recoup some of the cost of building green spaces and other river cleanup. In January, the office of D.C. Attorney General Brian Schwalb filed a lawsuit seeking unspecified damages from the federal government over decades of alleged pollution of the Anacostia River.

Brenda Lee Richardson, coordinator of the Anacostia Parks & Community Collaborative, said the efforts to cut down on trash and sewage are paying off. She sees a river on the mend, with more plant and animal life sprouting up.

“The ecosystem seems a lot greener,” she said. “There’s stuff in the river now that wasn’t there before.”

But any changes to the waterfront need to be done with residents of both sides of the river in mind, she said.

“We want there to be some sense of equity as it relates to who has access,” she said. “When I look at who is recreating, it’s not people who look like me.”

Richardson has lived for 40 years in Ward 8 — a predominantly Black area on the east side of the river whose residents are generally less affluent than those on the west side. She and her neighbors don’t consider the Anacostia a place to get out and play, she said.

As the water quality slowly improves, Richardson said, she hopes the Anacostia’s reputation is also rehabilitated. Even if it’s not safe to swim in, Richardson enjoys boating trips like the one with the Anacostia Riverkeeper.

“To see all those creatures along the way and the greenery. It was comforting,” she said. “So rather than take a pill to settle my nerves, I can just go down the river.”

KFF Health News is a national newsroom that produces in-depth journalism about health issues and is one of the core operating programs at KFF—an independent source of health policy research, polling, and journalism. Learn more about KFF.

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This article first appeared on KFF Health News and is republished here under a Creative Commons license.