By Paula Span, The New York Times
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 for further research after they died. “An amazing gift,” said Dr. Edward Lee, the neuropathologist who directs the brain bank at the university’s Perelman School of Medicine. The man, who died at 83 with dementia, had lived in 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, 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,” Dr. 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 in the suburb of Gladwyne, Pa., 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. “The quality of the air you live in affects your cognition,” said Dr. Lee, the senior author of a recent article in JAMA Neurology. In 2020, the influential Lancet Commission added air pollution to its list of modifiable risk factors for dementia.
“All these actions are going to decrease air quality and lead to increasing mortality and illness, dementia being one of those outcomes,” said Dr. John Balmes, a spokesman for the American Lung Association, referring to recent environmental moves by the White House. 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,” Dr. 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. With an environmental database, the researchers were able to calculate the participants’ 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.
Dr. 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 percent 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 (the second most common type), which includes dementia related to Parkinson’s disease.
Researchers in a study analyzed records from more than 56 million beneficiaries 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 Dr. 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. 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.
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,” Dr. Lee said. “So is dementia care.”