Breathing dirty air can quietly hurt your brain

A new analysis of nearly 30 million people confirms a disturbing link: prolonged exposure to outdoor air pollution increases the risk of dementia.

These findings are published in Lancet Planet Healthhighlights how flow exhaust, industry and burning fuel pollutants trigger processes in the brain, leading to memory loss and cognitive decline. Scientists say reducing pollution can reduce the global burden of dementia, which has affected more than 57 million people worldwide.

Three pollutants that increase the risk of dementia

Led by researchers from the MRC Epidemiology Department at the University of Cambridge, systematic reviews and meta-analysis extracted data from 51 studies from four continents, including more than 29 million participants. They found that dementia was statistically significant related to long-term exposure to three specific pollutants:

• PM2.5: The fine particles are less than 2.5 microns, which come from automobile exhaust, industrial emissions, and even fireplaces. 10 μg/m³ of PM2.5 exposure was associated with a 17% increase in the risk of dementia.
• Nitrogen dioxide (NO₂): In vehicle and industrial emissions, an increase in dementia risk increased by 3% per 10 μg/m³.
• Black carbon (smoke): Component from incomplete combustion PM2.5. Each increase of 1 μg/m3 is associated with a 13% increase in dementia risk.

In 2023, the average curbside levels in central London were PM2.5 and NO₂ of 10μg/m³ and 33μg/m³, respectively, meaningfully increasing the risk of dementia under these findings.

How dirty air affects the brain

What is the polluted air that affects the brain? According to the researchers, fine particles and gas can enter the brain directly through the nose or into the blood from the lungs. Once inside, they may cause inflammation and oxidative stress—two processes that damage brain cells and are known to cause dementia.

“Epidemiological evidence plays a crucial role in enabling us to determine whether air pollution increases the risk and amount of dementia,” said senior writer Dr. Haneen Khreis. “Responding to air pollution can lead to long-term health, social, climate and economic benefits.”

Which dementia is most affected?

While the evidence is most powerfully used in general dementia diagnosis, some contaminants appear to be in line with Vascular dementiaThis is caused by a decrease in blood flow to the brain. However, due to limited data, the difference between Alzheimer’s disease and vascular dementia was not statistically significant.

The researchers stress that most cases of dementia may involve a mixture of Alzheimer’s and vascular contributions, highlighting the complex nature of the diagnosis.

Bias and gaps in the data

Most of the studies included participants from high-income countries, mainly white populations. However, people in marginalized communities often face higher levels of pollution and may be more susceptible to it. The researchers call for representatives of larger low-income and middle-income countries in future research.

“For several pollutants, stricter restrictions may be needed,” said co-first author Clare Rogowski. “As to the extent of air pollution, regional, national and international policy interventions are urgently needed to combat air pollution in a fair manner.”

Policy, planning and prevention

The study adds calls to urban planners and public health officials to view air pollution as a modifiable risk factor for dementia, smoking, hypertension and inactivity.

“These findings highlight the need for interdisciplinary approaches to prevent dementia,” said co-first author Dr. Christiaan Bredell. “City planning, transportation policy and environmental regulation can all play a major role.”

By 2050, dementia cases are expected to be nearly triple to 152.8 million, and the authors of the study highlight that protecting air quality may be one of the few tools currently available to slow this rising trend.

refer to

Best Rogowski, CB, Bredell, C. wait. “Long-term air pollution exposure and event dementia: a systematic review and meta-analysis.” Lancet Planet HealthJuly 24, 2025. DOI: 10.1016/S2542-5196 (25) 00118-4

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