A major new study has found that long-term exposure to air pollution—such as emissions from cars and industry—can significantly increase the risk of developing dementia.
The research, led by scientists at the Medical Research Council (MRC) Epidemiology Unit at the University of Cambridge, analyzed data from nearly 30 million people worldwide and found strong links between certain pollutants and the onset of dementia.
Dementia, including Alzheimer’s disease, currently affects over 57 million people around the world, and this number is expected to rise to nearly 153 million by 2050. The growing burden on individuals, families, caregivers, and healthcare systems is immense.
In their study, published in The Lancet Planetary Health, the research team reviewed 51 previously published studies from Europe, North America, Asia, and Australia. Thirty-four of these studies, involving over 29 million participants, were used in a detailed meta-analysis.
The results showed a clear connection between three key types of air pollution and higher dementia risk:
– Fine particulate matter (PM2.5), tiny particles that are small enough to be inhaled deeply into the lungs, mainly from vehicle exhaust, industrial activity, and wood burning.
– Nitrogen dioxide (NO2), mostly from burning fossil fuels like car engines, gas stoves, and industrial emissions.
– Soot (a component of PM2.5), from sources such as car exhaust and wood burning.
According to the researchers, every increase of 10 micrograms per cubic meter (μg/m³) of PM2.5 raises the risk of dementia by 17%. For NO2, the risk increases by 3% for each 10 μg/m³, and for soot, a 1 μg/m³ rise leads to a 13% increased risk.
These pollution levels are common in large cities—average PM2.5 levels in Central London, for example, were around 10 μg/m³ in 2023.
Dr. Haneen Khreis, senior author of the study, explained that the evidence strongly supports the idea that air pollution is a real risk factor for dementia. “Tackling air pollution,” she said, “can bring long-term health, climate, and economic benefits, while also reducing the enormous burden dementia places on families and healthcare systems.”
Researchers believe air pollution could cause dementia by triggering inflammation in the brain and oxidative stress, a process that damages cells and DNA. These changes can contribute to brain diseases like Alzheimer’s and vascular dementia.
Pollutants may enter the brain directly or travel from the lungs through the bloodstream, spreading inflammation throughout the body.
Although most of the data came from studies involving white populations in wealthy countries, researchers noted that people in poorer or marginalized communities are often exposed to higher levels of pollution. They called for future research to include more diverse populations, especially from low- and middle-income countries.
Joint first author Clare Rogowski said stricter pollution controls—particularly targeting vehicles and industrial emissions—will likely reduce dementia rates. She emphasized the need for urgent policy action at local, national, and international levels.
Interestingly, the study also found that while pollution raised the risk for all types of dementia, the link appeared stronger for vascular dementia, which is caused by reduced blood flow to the brain. However, more studies are needed to confirm this finding.
Dr. Christiaan Bredell, another lead author, summed it up by saying that preventing dementia isn’t just a health issue. Urban design, transportation, and environmental rules all play a part. This study shows that fighting pollution could also help fight dementia.
If you care about brain health, please read studies about inflammation that may actually slow down cognitive decline in older people, and low vitamin D may speed up cognitive decline.
For more information about brain health, please see recent studies about common exercises that could protect against cognitive decline, and results showing that this MIND diet may protect your cognitive function, prevent dementia.
The study is published in The Lancet Planetary Health.
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