Marlene Cimons
THE WASHINGTON POST – Breathing in microscopic air pollutants may raise the risk of developing dementia, according to a new analysis of existing research by public health scientists at Harvard.
It has long been known that inhaling these microscopic particles, also known as PM 2.5, particles less than 2.5 microns in width can cause serious health issues. (In comparison, the width of a single human hair is 50 to 100 microns).
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.”
More than 57 million people globally are living with dementia, a number expected to increase to an estimated 153 million by 2050.
The meta-analysis, published on Wednesday in the British Medical Journal (BMJ), examined 16 observational studies and found consistent evidence of a connection between PM 2.5 and dementia, even when an individual’s annual exposure was less than 12 microgrammes per cubic metre of air, which is the current Environmental Protection Agency (EPA) standard, the study said.
A grain of rice, in comparison, weighs about 30,000 microgrammes, Weisskopf said.
The studies measured the dementia subjects’ overall exposure to pollutants from one year to up to 20 years, although “it’s unlikely that the dementia-causing exposure is actually as low as one year, but the researchers use that number as a surrogate to estimate longer-term exposure”, Weisskopf said.
The EPA is considering strengthening air quality standards to lower PM 2.5 exposure to a level between nine and 10 microgrammes annually, or between eight and 11 microgrammes per cubic meter of air. The agency has asked for public comments on both measures.
Ninety-nine per cent of the global population is exposed to PM 2.5 levels considered unhealthy – annual concentrations higher than five microgrammes per cubic metre – by the World Health Organization, according to a study published last month.
INCREASED PM 2.5 EXPOSURE LINKED WITH INCREASED DEMENTIA RISK
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 eliminate biases that can influence the outcome, for example inequities in healthcare access and the extent of pollutant exposure, Weisskopf said.
They found a 17-per-cent rise in dementia risk for every two-microgramme increase per cubic metre of air of annual PM 2.5 exposure, as well as smaller increases in risk from breathing nitrogen oxide and nitrogen dioxide, pollutants that most often result from traffic exhaust.
It’s unclear how air pollution influences the development of dementia, said senior director of scientific engagement for the Alzheimer’s Association Rebecca Edelmayer, but “it’s hypothesised that the very small particles of pollutants enter our bodies and penetrate our circulatory system, which helps fuel the brain”. Some scientists speculate it might be related to chronic inflammation in the body, or the build-up of beta amyloid levels in the blood.
The brains of Alzheimer’s disease patients often have abnormal levels of beta amyloid that 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.
PM 2.5 contaminants often come from construction sites, unpaved roads, smokestacks and fires, or are complex chemical reactions from pollutants emitted from power plants, industrial facilities, cars and trucks.
“Most people do not have the ability to 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 the clinical director of George Washington University’s Institute for Brain Health and Dementia Christina Prather 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.”
Moreover, these pollutants disproportionately hurt vulnerable populations such as children, older people and those with existing heart or lung diseases, as well as low-income neighbourhoods and communities of colour, where polluting industries frequently locate.
“The story of dementia and disparity and race is very real,” Prather said. The American Lung Association, in its 2022 State of the Air report, found that more than four in 10 Americans live in areas with unhealthy air quality.
DEMENTIA AMONG MANY HEALTH ISSUES LINKED TO AIR POLLUTION
The latest study adds dementia to the numerous dangers of air pollution documented by a growing body of scientific research in recent years.
Many studies, including a June 2022 report from the Health Effects Institute, have linked air pollution to health problems such as heart disease and stroke, low birth weight, circulatory problems, lung cancer mortality, worsening of asthma, especially in children, diabetes, cognitive decline and birth defects, and early death.
Research also has linked air pollution exposure to such social effects as substance abuse, self-harm, suicide and crime.
This contamination fouls the air and heats up the planet, underscoring the dangers of climate change, experts said.
“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 a physician and Health Equity Fellow at the Centre for Climate, Health and the Global Environment at the Harvard T H Chan School of Public Health Gaurab Basu 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.”
Basu said that as a primary care physician, he regularly sees the “distressing impacts of dementia” on his patients and their loved ones.
Many people are exposed to air pollution, and lowering their exposure could make a huge difference in the overall global burden of dementia, both now and in the future, with substantial population-level health impacts, Weisskopf said.
“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.
