Long-term exposure to air pollution may be linked to a higher risk of dementia, faster biological ageing and changes in brain structure, according to a UK study. The findings add to evidence that polluted air may affect more than the lungs and heart, raising questions about how environmental exposure could influence brain health.
Published in April in the Journal of Nutrition, Health & Aging, the study analysed 488,348 UK Biobank participants who did not have dementia at the start. Researchers compared exposure to several pollutants with health outcomes over nearly 14 years, during which 9,000 dementia cases were recorded.
People with the highest exposure to fine particulate matter, known as PM2.5, had a 14% higher risk of developing dementia than those with the lowest exposure. Higher exposure to other pollutants was also associated with increased risk: nitrogen dioxide was linked to a 20% higher risk, while nitrogen oxides were associated with a 14% increase.
These figures describe relative risk, not the likelihood that a person will develop dementia. The research found an association, not proof that pollution directly causes the disease. Exposure estimates based on environmental data may also differ from each participant’s actual exposure at home, work or while travelling.
PM2.5 consists of tiny airborne particles that can travel deep into the lungs. Some components can enter the bloodstream, while researchers are investigating whether particles may also reach the brain through pathways that remain unclear. Sources include vehicle exhaust, industrial activity and fuel combustion.
Greater pollution exposure was associated with lower brain volume and changes in several brain regions. Researchers also assessed biological ageing using health indicators that estimate how old a person’s body appears. Their analysis suggested that accelerated ageing and brain atrophy may partly explain the relationship between pollution and dementia.
The results add to other research into polluted air and the brain. A study published in May in Environmental Pollution followed nearly 270,000 people for 14 years. It linked higher PM2.5 exposure with structural changes in the hippocampus, a region important for learning and memory. Inflammation and changes in fat metabolism appeared to explain a small part of the association.
Scientists are also investigating whether pollution can affect brain tissue directly, rather than only through inflammation elsewhere in the body. A Washington Post report on October 22 described research examining brain tissue from 11 people aged 80 to 91. Researchers found particles including metals, soot, silica and microplastics deep in the brain, including in the amygdala, which helps regulate emotion and memory. The small study cannot show how the particles arrived or what effects they had, but it adds to questions about how airborne material may interact with the brain.
Laboratory studies offer clues, although animal findings cannot automatically be applied to humans. Research published in Science in 2025 found that pollution exposure in mice triggered abnormal accumulation of alpha-synuclein, a protein associated with Lewy bodies. These deposits are linked to Lewy body dementia and Parkinson’s disease dementia. Exposed mice also showed brain damage and cognitive decline, while animals engineered without the protein experienced less of some effects.
In a September experiment, researchers compared diesel exhaust, dust from the World Trade Center site and wood smoke in mice. Diesel exhaust and the dust altered many of the same genes, including those involved in inflammation and amyloid processing. Both contained metals, prompting researchers to consider whether the composition of pollution may matter as much as its concentration. Further studies are needed to understand how these findings apply to people.
Individuals cannot eliminate air pollution, but steps may reduce exposure. These include checking local air-quality reports, improving ventilation while cooking, maintaining indoor air filters and limiting strenuous outdoor activity when pollution levels are high. Traffic pollution can be greater near busy roads, and cooking can produce high particle levels indoors when ventilation is poor.
The findings do not mean that everyone exposed to polluted air will develop dementia. Dementia has multiple risk factors, including age, genetics and cardiovascular health. Researchers say more work is needed to identify the most harmful pollutants, determine when exposure matters most and establish whether reducing exposure can lower dementia risk.
The evidence strengthens the case for treating clean air as a public-health priority. Air pollution is already associated with heart and lung disease, and scientists are increasingly studying its possible role in brain ageing. Understanding the link could help guide environmental policy and prevention efforts, while highlighting that brain health is shaped by environmental conditions as well as individual choices.
