Scientists are growing more confident that air pollution—especially from particulate matter less than 2.5 microns wide, known as PM 2.5—significantly raises the risk of Alzheimer’s disease and other forms of dementia, according to a series of separate studies published in July.
The link between neurological disease and air pollution has been suspected for some time, and now data are accumulating to back it up. In one study published July 26, scientists at the University of Southern California found that among women in the US aged 74-92, a 10% decrease in ambient PM 2.5 in the area surrounding their home reduced their likelihood of developing dementia by 14%. A similar study published the same day of people over age 65 in France found a 17% decrease in the likelihood of Alzheimer’s for every microgram of pollutant per cubic meter of air. And a third, published July 9, found that in North Carolina zip codes with elevated levels of PM 2.5, the rate of hospitalizations and deaths from Alzheimer’s and other forms of dementia was significantly higher than in zip codes with lower levels of PM 2.5. Each of the studies controlled for potentially confounding variables like differences in race and gender (Alzheimer’s is more common in women and in Black people), smoking, and the presence of other environmental pollutants like arsenic in soil.
“It’s already well documented that exposure to PM 2.5 is associated with cardiovascular and other diseases, but within the last few years the number of publications is rising on an increased risk for brain tissue,” said Yuliya Krauchanka, a professor of surgery at the Duke University School of Medicine and co-author of the North Carolina study. “But the brain is usually the most well-protected organ in the body, so it’s a very alarming situation when we see toxins sneaking in through this barrier.”
A warning for countries with air pollution problems
Air pollution is far from the most decisive factor for dementia risk, Krauchanka said. About 70% of risk stems from an individual’s genetic predisposition to the disease, and the remainder comes down to age, and lifestyle and environmental factors. Still, all else being equal, PM 2.5 pollution clearly substantially elevates risk, and that conclusion should be a concern for countries where it remains elevated, she said. Although the total global concentration of PM 2.5 has fallen dramatically in recent decades because of more rigorous clean air regulations in countries in the global north, half of the world’s population lives in countries where PM 2.5 is rising. South Asia is especially at risk: Bangladesh, Pakistan, and India rank highest in the world. In all three, median age and life expectancy are rising, meaning that a dementia boom is likely around the corner (in sub-Saharan Africa, where PM 2.5 is also high, life expectancy remains in the low 60s, below the age at which most people develop dementia regardless of environmental factors, Krauchanka said).
That’s not only a tragedy for the individuals and families who are affected—it’s also a major drag on the economy. Alzheimer’s is the third most-costly condition in the US after cancer and heart disease, setting the country back $355 billion every year in costs related to skilled nursing care, home healthcare, hospice care, in addition to less easily measured costs from informal caregiving.