New research suggests a direct link between long-term exposure to air pollution and an increased risk of Alzheimer’s disease, even after accounting for other common health factors. The findings, published in in PLOS Medicine, add to a growing body of evidence highlighting the impact of environmental factors on neurological health.
For years, air pollution has been recognized as a risk factor for conditions like hypertension, stroke and depression – all of which are also associated with an increased risk of Alzheimer’s. However, it remained unclear whether air pollution primarily contributed to Alzheimer’s by first triggering these other health problems, or if it had a more direct effect on the brain itself. This new study suggests the latter is, at least in part, true.
Researchers at Emory University analyzed health records of over 27.8 million US citizens aged 65 and older, spanning from to . Approximately three million individuals within that cohort were diagnosed with Alzheimer’s disease during the study period. The team then correlated these diagnoses with estimated levels of fine particulate matter (PM2.5) – microscopic air pollutants – in the participants’ residential ZIP codes.
PM2.5, measuring 2.5 micrometers in diameter or less, is considered particularly dangerous because of its ability to penetrate deep into the lungs and even enter the bloodstream. Sources of PM2.5 include vehicle emissions, power plant emissions, industrial processes, wildfires, and the burning of wood or fossil fuels for heating.
The study’s analysis revealed that exposure to higher levels of air pollution was associated with a greater risk of developing Alzheimer’s disease. Importantly, this association remained significant even after researchers accounted for the presence of hypertension, stroke, and depression. “Our findings suggest that PM2.5 exposure was associated with increased Alzheimer’s disease risk, primarily through direct rather than comorbidity-mediated pathways,” the researchers wrote.
The link between air pollution and Alzheimer’s appeared to be even stronger among individuals with a prior history of stroke, suggesting that pre-existing vascular damage may increase vulnerability to the harmful effects of air pollution on brain health. “Our findings suggest that individuals with a history of stroke may be particularly vulnerable to the harmful effects of air pollution on brain health, highlighting an important intersection between environmental and vascular risk factors,” the study authors noted.
This research builds upon earlier findings linking air pollution to neurodegenerative diseases. A study from Penn Medicine, published in , found that exposure to high concentrations of air pollution correlated with increased buildup of amyloid plaques and tau tangles – hallmark proteins of Alzheimer’s pathology – in the brains of Alzheimer’s patients, accelerating cognitive decline. That study examined post-mortem brain tissue and found a clear correlation between pollution exposure and the severity of these pathological changes.
While the Emory University study provides compelling evidence, it’s important to acknowledge its limitations. Researchers relied on ZIP code-level data to estimate individual exposure to PM2.5, rather than precise measurements at each participant’s address. The study focused solely on outdoor air pollution, and did not account for potential indoor sources of particulate matter, such as cooking or heating.
Despite these limitations, experts agree that the findings are significant. Mark Dallas, from the University of Reading, who was not involved in the research, commented that the results align with a growing body of evidence suggesting that air pollution is a modifiable risk factor for dementia. “Because the study relies on broad estimates of pollution and medical records, You’ll see important limitations, but the results are consistent with increasing evidence that air pollution is a modifiable risk factor for dementia,” he said.
The implications of these findings are far-reaching, given the increasing global prevalence of Alzheimer’s disease. More than 55 million people worldwide are currently living with dementia, with Alzheimer’s disease accounting for up to 70 percent of cases, according to the World Health Organization. With global populations aging, the number of individuals affected by Alzheimer’s is projected to continue rising in the coming years.
Many countries have set goals to reduce air pollution levels, but most are likely to fall short of achieving desired targets by . The World Health Organization’s 2021 “Global Air Quality Guidelines” provide benchmarks for acceptable levels of particulate matter. The WHO’s 2025 roadmap, endorsed by the World Health Assembly, aims to reduce deaths attributable to air pollution by 50 percent by , compared to levels, with a particular focus on PM2.5.
“The implications of this US study are global; air pollution is a challenge we need to face together,” says Sheona Skils, Director of Research at Alzheimer’s Research UK. “Setting stronger, health-based air quality targets and reducing exposure to pollution will help protect our brains, as well as our lungs, and may lower the risk of dementia overall.”
In Europe, approximately 12.1 million people were living with dementia in , with women accounting for around 66 percent of cases. As populations continue to age worldwide, the number of people affected by dementia is expected to increase in the years ahead, underscoring the urgent need for preventative measures, including addressing air pollution.
