Air Pollution May Increase the Risk of Dementia

Taking in microscopic air pollutants may increase the risk of dementia, according to a recent review of the literature by Harvard public health researchers. It has long been understood that breathing in these tiny particles, commonly referred to as PM 2.5 or particles with a width of fewer than 2.5 microns, can have detrimental effects on one's health. (In comparison, the width of a single human hair is 50 to 100 microns.)

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Harvard Researchers Find Link Between Air Pollution and Dementia

But “their relationship to the brain and dementia is a relatively recent thing,” said lead study author Marc Weisskopf, Cecil K. and Philip Drinker Professor of environmental epidemiology and physiology at Harvard T.H. Chan School of Public Health. “Dementia is a massive problem worldwide. If we can reduce exposure to these particles, we can reduce the burden of dementia.”

Globally, more than 57 million individuals have dementia, and by 2050, that figure is projected to rise to 153 million.

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Link Between Air Pollution and Dementia Supported by 16 Observational Studies

The meta-analysis, which was released in the British Medical Journal (BMJ), looked at 16 observational studies and discovered consistent evidence of a link between PM 2.5 and dementia, even when a person's annual exposure was below the current Environmental Protection Agency standard of 12 micrograms per cubic metre of air, according to the study. According to Weisskopf, a grain of rice has a mass of around 30,000 micrograms.

The studies measured the dementia subjects' overall exposure to pollutants from one year to up to 20 years. "It's unlikely that the dementia-causing exposure is as low as one year," Weisskopf said, "but the researchers use that number as a surrogate to estimate longer-term exposure."

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EPA to Consider Tightening Air Quality Standards Amid Health Concerns

The EPA is considering tightening air quality standards to limit PM 2.5 exposure to nine to ten micrograms per year or eight to eleven micrograms per cubic metre of air. The agency has requested public feedback on both measures.

According to a study published last month, 99% of the global population is exposed to PM 2.5 levels considered unhealthy by the World Health Organization — annual concentrations greater than five micrograms per cubic metre.

Increased PM 2.5 exposure has been linked to an increased risk of dementia.

The Harvard scientists examined studies that used a method known as “active case ascertainment,” a process where every participant is screened with an extensive work-up to confirm a dementia diagnosis, Weisskopf said. This approach is more accurate than “passive case containment,” which involves random screening and “can miss many cases,” Weisskopf said.

They also used a more precise software tool to remove biases that could influence the outcome, such as disparities in healthcare access and the extent of pollutant exposure, according to Weisskopf.

They discovered a 17% increase in dementia risk for every two-microgram increase per cubic metre of air in annual PM 2.5 exposure, as well as smaller increases in risk from breathing nitrogen oxide and nitrogen dioxide, pollutants most commonly caused by traffic exhaust.

How Air Pollution May Influence the Development of Dementia

According to Rebecca Edelmayer, senior director of scientific engagement for the Alzheimer's Association, it's unclear how air pollution influences the development of dementia, but "it's hypothesised that very small particles of pollutants enter our bodies and penetrate our circulatory system, which helps fuel the brain."

Some scientists believe it is related to chronic inflammation in the body or an increase in beta-amyloid levels in the blood. Alzheimer's disease patients' brains frequently have abnormal levels of beta-amyloid, which clump together to form plaques that disrupt neurons and cell function.

“These data illustrate that there are many factors across the life course that can contribute to our risk of dementia, and this includes the environment,” Edelmayer said.

Polluting Industries and Vulnerable Populations at Higher Risk of Air Pollution-Related Health Problems

Construction sites, unpaved roads, smokestacks, and fires are common sources of PM 2.5 contaminants, as are complex chemical reactions from pollutants emitted by power plants, industrial facilities, cars, and trucks.

“Most people cannot control or influence the quality of the air they breathe in their environment, so this is not a personal risk they can manage themselves,” said Christina Prather, the clinical director of George Washington University’s Institute for Brain Health and Dementia who was not involved in the study. “For most individuals, a diagnosis of dementia is something they dread because — outside of living as best, they can with it — there isn’t much we can do to reverse it. So any work that allows us to identify risk factors and prevent people from developing dementia is something we need to pay attention to.”

Furthermore, these pollutants disproportionately harm vulnerable populations such as children, the elderly, and those with pre-existing heart or lung diseases, as well as low-income neighbourhoods and communities of colour, which are frequently home to polluting industries. "The story of dementia, disparity, and race is very real," said Prather.

According to the American Lung Association's 2022 "State of the Air" report, more than four out of every ten Americans live in areas with poor air quality.

Dementia: A New Addition to the Long List of Health Risks Associated with Air Pollution

Dementia is one of many health problems linked to air pollution. The latest study adds dementia to the long list of health risks associated with air pollution, as documented by a growing body of scientific research in recent years.

Many studies, including a report released in June 2022 by the Health Effects Institute, have linked air pollution to health issues such as heart disease and stroke, low birth weight, circulatory problems, lung cancer mortality, asthma worsening, particularly in children, diabetes, cognitive decline and birth defects, and premature death.

Air pollution has also been linked to social effects such as substance abuse, self-harm, suicide, and crime, according to research.

According to experts, this pollution pollutes the air and heats the planet, emphasizing the dangers of climate change.

“This meta-analysis reinforces my belief that ending the use of fossil fuels is the most critical intervention we can take to protect people’s health,” said Gaurab Basu, a physician and Health Equity Fellow at the Center for Climate, Health and the Global Environment at the Harvard T.H. Chan School of Public Health who was not involved in the research. “This study helps us bring cognitive health to the forefront of the conversation of benefits we derive from rapidly transitioning to a clean energy economy.”

As a primary care physician, Basu sees the "distressing impacts of dementia" on his patients and their loved ones regularly.

Many people are exposed to air pollution, and reducing their exposure could make a significant difference in the overall global burden of dementia, both now and in the future, with significant population-level health consequences, according to Weisskopf.

“Dementia has a tremendous personal, health, societal and financial cost to the world, so anything we can do to delay, modify or prevent can have massive societal implications,” he said.

Source-Medindia