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Illustration of Mother Jones; Getty
A few years ago, I was in a narrow caravan next to the busy Highway 110 in Los Angeles, while researchers from the University of Southern California were collecting soot thrown by striking vehicles to a few meters of their instruments, which shook every time a heavy truck passed. I was there to understand how scientists were beginning to associate air pollution – from power plants to motorized vehicles, to forest fires, and so on. – to one of the least understood and scary diseases: dementia.
At that time, as I reported in Mother Jones, the research that air pollution was one of the factors that could contribute to dementia was alarming, consistent and, ultimately, "suggestive". Since then, scientists have published a series of studies that reveal that air pollution is far more serious for us than we did before. conceived. The evidence is so convincing, in fact, that many reputable researchers now think they are conclusive. "I absolutely do not hesitate to say that air pollution is the cause of dementia," says Caleb Finch, a gerontologist and head of USC's pollution research network. Air and brain diseases, which has led to many of these new studies. In terms of its effects on our health and well-being, Finch says, "air pollution is as serious as cigarette smoke." This evidence parallels the alarming news that the air quality is actually deterioration for many cities in the United States, while the Trump administration continues its efforts to delay or cancel the measures to protect the environment.
What makes Finch – and the half dozen other researchers I've talked to – so sure? Of all the new research, three studies in particular paint a striking picture of how our air quality can determine whether we will age with our intact mind. In one of 2018, researchers followed 130,000 elderly people living in London for several years. People exposed to higher levels of air pollutants, particularly nitrogen dioxide and fine particles released from burning fossil fuels, were far more likely to develop Alzheimer's disease – the most common type of dementia – only their counterparts with the same demographic characteristics. In total, Londoners exposed to the highest levels of air pollution were about one and a half times more likely to develop Alzheimer's disease during the study period than their exposed neighbors at the highest levels. low – a replica of previous Taiwan results, where air pollution levels are much higher.
Another, a 2017 study published in the Lancet, followed all adults living in Ontario (approximately 6.5 million people) for more than 10 years and finding that people living near busy highways were significantly more likely to develop Alzheimer's disease during the the study, regardless of their initial state of health or their socio-economic status. Both of these studies estimated that about 6-7% of all cases of dementia in their samples could be attributed to exposure to air pollution.
These studies in Canada and the United Kingdom are certainly intriguing. But the most compelling, and the least reported, study comes from the United States. Incidentally, he was also inspired by our previous reports.
Following our preliminary report on the link between air pollution and dementia, three economists from the University of Arizona – Kelly Bishop, Nicolai Kuminoff and Jonathan Ketcham – decided to conduct a large-scale inquiry into the issue. "We found the Mother Jones convincing article, "says Ketcham. "It was instructive about plausible pathways and the need for more rigorous studies that could test causality."
In the end, Bishop, Kuminoff and Ketcham decided to link the EPA data on air quality to fifteen years of Medicare records for 6.9 million older Americans. 65 years old. Rather than simply asking whether Americans exposed to greater air pollution were developing dementia at higher rates, the team identified an almost natural experience that arbitrarily separated Americans into more or less exposed to air pollution. In 2005, the US Environmental Protection Agency targeted increased regulation in 132 counties in 21 US states as they violated new air quality standards for fine particle pollution. As a result, residents of these counties have seen their air quality improve faster than their counterparts with equivalent demographic characteristics living in other counties that initially had equal exposure but lived in counties with low-income counties. levels of pollution just below the new air quality standards.
This quirk of different standards across the country has allowed researchers to ask if a decreased manipulation Indeed, exposure to air pollution has actually resulted in fewer cases of dementia, due to Alzheimer's disease or other dementia-related diseases, such as stroke. This overcame a significant limitation of other existing studies, which could only compare differences in exposure and illness occurring "naturally" between people living in different locations rather than a planned intervention. "If people who are less educated, less fortunate and less healthy for unknown reasons end up living in more polluted areas," says Ketcham, "it is hard to say which of these factors could have led to the disease. "
As they told National Office of Economic Research last year, Bishop, Kuminoff and Ketcham determined that air pollution could actually cause dementia, especially Alzheimer's dementia. In countries that needed to quickly comply with the new air quality standards, older people developed Alzheimer's disease at a lower rate than their peers in countries where the new rules did not apply. The annual exposure to an average of an extra microgram of fine particle pollution per cubic meter of air (a much lower amount than the difference you might experience if you passed from one neighborhood clean to a more polluted neighborhood) increased dementia as if they had aged another 2.7 years. The authors estimated that the magnitude of this high risk was close to that of other drivers known for dementia, including hypertension and heart disease.
Ketcham adds that the application of the EPA's more stringent air quality standard has likely resulted in a reduction of 140,000 people with dementia by the end of the year. 2014. It estimates at about $ 163 billion the economic value of this prevented burden of disease.
Researchers now understand better what happens in the brain when you breathe in polluted air – and how that can lead to neurodegeneration years later. When you inhale pollutants, the smallest particles emitted by cars, power plants and other places where fuel is burned, lodge in the sensitive tissues of your lungs or pass into your bloodstream. In these places, they trigger an immune response that seeks to trap, contain and eliminate invasive particles. Over time, this response spreads to what we call "systemic inflammation" or an overactive and overactive immune response throughout the body.
According to Caleb Finch, systemic inflammation appears to be the primary means by which air pollution harms the brain. In early 2017, Finch and colleagues showed that inflammation from exposure to air pollution led to the formation of Alzheimer's plaques in the brains of genetically modified mice to develop the pathology of Alzheimer's disease. "It was impressive," says George Martin, director emeritus of the Alzheimer's Research Center at the University of Washington, who was not involved in the study. Because of this study and other similar studies, Martin now thinks that air pollution could be a potential cause of dementia, although he wants more data on mechanisms and "ideally , on one or more specific components of air pollution ".
In the coming years, these new discoveries could influence scientists' understanding of neurodegenerative diseases. Because of these new studies, says George Perry, senior scientist at the Brain Health Consortium of the University of Texas at San Antonio and editor of the Journal of Alzheimer's Alzheimer's, "my vision of Alzheimer's is Perry now thinks that air pollution is a potential risk factor for dementia and his Alzheimer's diary will soon publish a special issue dedicated to the connection between them. Motivated, in part, by the new evidence, Perry is also increasingly seeing dementia as a disease such as cancer, where multiple factors could lead to a pathology. "People develop cancer without smoking or exposure to air pollution," he says, "but each of these factors will increase your risk."
Unlike smoking, we can not always know when we are exposed to stale air and we can not decide when to quit. Arizona State's Kuminoff is a firm believer that we could avoid more dementia by strengthening our existing standards for air pollution. If there is a safe level of exposure, he says, "We have not arrived yet."
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