For years, both patients came 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 of people with normal cognitive abilities.
Both patients, a man and a woman, agreed to donate their brains after death for further research. “It’s an amazing gift,” said Edward Lee, the neurologist who heads the department. brain bank at the university's Perelman School of Medicine. “They were both very committed to helping us understand Alzheimer's disease.”
The man, who died at 83 of dementia, lived in the Center City area of Philadelphia with paid caregivers. An autopsy revealed large amounts of amyloid plaques and tau tangles, proteins associated with Alzheimer's disease, spreading throughout his brain.
Researchers also found infarcts, small patches of damaged tissue, indicating he had suffered multiple strokes.
In contrast, the woman, who was 84 when she died of brain cancer, “had almost no Alzheimer's pathology,” Lee said. “We tested her year after year and she had no cognitive problems at all.”
The man lived a few blocks from Interstate 676, which runs through downtown Philadelphia. The woman lived a few miles away, in the suburb of Gladwin, Pennsylvania, surrounded by woods and a country club.
The amount of air pollution she was exposed to – specifically levels of fine particulate matter called PM2.5 – was half her exposure. Was it a coincidence that he developed severe Alzheimer's disease while she remained cognitively normal?
Given the growing evidence that chronic exposure to the neurotoxin PM2.5 not only damages the lungs and heart, but is also linked to dementia, probably not.
“The air quality you live in affects how you think,” said Lee, senior author of the recent study. article in JAMA Neurologyone of several large studies in recent months showing a link between PM2.5 and dementia.
Scientists have been tracking this connection for at least a decade. In 2020, the Lancet's influential commission added air pollution to its list of modifiable risk factors for dementia, as well as common problems such as hearing loss, diabetes, smoking and high blood pressure.
However, the findings come as the federal government rolls back efforts by previous administrations to further reduce air pollution by shifting away from fossil fuels to renewable energy sources.
“'Drain, baby, train' is just the wrong approach,” said John Balmes, a spokesman for the American Lung Association who studies the health effects of air pollution at the University of California, San Francisco.
“All of these actions will degrade air quality and lead to increased mortality and morbidity, one of which is dementia,” Balmes said, referring to the White House's recent environmental measures.
Of course, many factors contribute to dementia. But the role of particulate matter—microscopic particulate matter or droplets in the air—is coming under increasing scrutiny.
Particulate matter comes from many sources: emissions from power plants and home heating, factory fumes, vehicle exhaust and, increasingly, smoke from wildfires.
Of the several particle sizes, PM2.5 “appears to cause the most harm to human health” because it is one of the smallest, Lee said. Easily inhaled particles enter the bloodstream and circulate throughout the body; they can also travel directly from the nose to the brain.
The University of Pennsylvania study, the largest autopsy study of people with dementia to date, included more than 600 brains donated over two decades.
Previous studies of environmental pollution and dementia have mainly relied on epidemiological studies to establish an association. Now, “we're linking what we actually see in the brain to pollutant exposure,” Lee said, adding, “We can take a deeper dive.”
Study participants underwent years of cognitive testing at Penn Memory. With a database of environmental data, the researchers were able to calculate PM2.5 exposure based on their home addresses.
The scientists also developed a matrix to measure how much Alzheimer's disease and other dementias damaged donors' brains.
Lee's team concluded that “the higher the exposure to PM2.5, the higher the severity of Alzheimer's disease,” he said. The odds of more severe Alzheimer's pathology at autopsy were nearly 20% higher among donors who lived where PM2.5 levels were high.
Another research group recently reported connection between PM2.5 exposure and dementia with Lewy bodies, which includes dementia associated with Parkinson's disease. Lewy bodies, generally considered the second most common type after Alzheimer's disease, account for 5% to 15% of dementia cases.
In what the researchers say is the largest epidemiological study of pollution and dementia to date, they analyzed the records of more than 56 million traditional health care recipients from 2000 to 2014, comparing their initial hospitalizations for neurodegenerative diseases with their exposure to PM2.5 by zip code.
“Chronic exposure to PM2.5 was associated with hospitalization for Lewy body dementia,” said Xiao Wu, study author and biostatistician at Columbia University's Mailman School of Public Health.
After accounting 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 PM2.5 concentrations than in counties with the least.
To test their findings, the researchers administered PM2.5 nasally to laboratory mice, which after 10 months showed “obvious dementia-like impairments,” senior author Xiaobo Mao, a neuroscientist at Johns Hopkins School of Medicine, wrote in an email.
The mice got lost in the labyrinths through which they had previously rushed. Previously, they built nests quickly and compactly; their efforts were now sloppy and disorganized. At autopsy, Mao said, their brains were atrophied and contained clumps of a protein associated with Lewy bodies in the human brain called alpha-synuclein.
A third analysispublished this summer in The Lancet, included 32 studies conducted in Europe, North America, Asia and Australia. It also found that “a diagnosis of dementia was significantly associated with long-term exposure to PM2.5” and several other pollutants.
Whether so-called outdoor air pollution increases dementia due to inflammation or other physiological causes awaits the next round of research.
Although air pollution in the United States has fallen over two decades, scientists are calling for even stronger action to ensure cleaner air. “People argue that air quality is expensive,” Lee said. “So is dementia care.”
However, President Donald Trump took office again, promising to increase extraction and use of fossil fuels and block the transition to renewable energy. His administration canceled tax breaks for solar installations and electric vehicles, Balmes noted, adding: “They encourage us to continue burning coal to produce electricity.”
The administration has stopped the construction of new offshore wind farmsannounced oil and gas drilling in the Arctic National Wildlife Refuge in Alaska and moved to stay California Plan switch to electric vehicles by 2035. (The state challenged this action in court.)
“If the policy goes in the opposite direction, with air pollution increasing, it will become a greater health risk for older people,” Wu said.
Last year, under the Biden administration, the Environmental Protection Agency set more stringent annual standards for PM2.5, noting that “available scientific evidence and technical information indicate that current standards may not be sufficient to protect public health and welfare as required by the Clean Air Act.”
In March, the Environmental Protection Agency new chairman announced that the agency would be “revisiting” these more stringent standards.
New Old Age is created in collaboration with New York Times.
KFF health news is a national newsroom that produces in-depth journalism on health issues and is one of the core operating programs of KFF, an independent source of health policy research, polling and journalism. Find out more about KFF.
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