A groundbreaking study has found that long-term exposure to fine-particulate air pollution can significantly increase the risk of Lewy body dementia—a progressive neurodegenerative disease that is one of the most common forms of dementia. The research, led by scientists at Johns Hopkins University, sheds new light on how environmental factors, particularly airborne pollutants, can contribute to the onset of severe brain diseases.

Published in the journal Science, the study demonstrates how exposure to PM2.5 particles—tiny pollutants less than 2.5 micrometres in diameter—can trigger the formation of toxic protein clumps in the brain. These protein aggregates, known as Lewy bodies, are made up of misfolded alpha-synuclein, a protein essential to normal brain function. In their abnormal form, however, these clumps spread through the brain, killing nerve cells and leading to significant cognitive decline.

Lewy body dementia is the third most common form of dementia, after Alzheimer’s disease and vascular dementia. It is characterised by symptoms such as memory loss, confusion, visual hallucinations, and motor control issues, and it currently affects millions of people worldwide.

“This finding has profound implications,” said Dr Xiaobo Mao, the study’s lead investigator and a neurologist at Johns Hopkins University. “Unlike age or genetic predisposition, air pollution is a modifiable risk factor. That means we have the power to take steps to prevent or reduce its impact.”

To investigate the connection between air pollution and dementia, the research team analysed medical records of 56.5 million U.S. Medicare patients. The data covered individuals admitted to hospital for the first time between 2000 and 2014 with signs of protein damage consistent with neurodegenerative diseases. Using patient zip codes, researchers estimated long-term exposure levels to PM2.5 in their residential areas.

The study found a clear link: patients with higher exposure to PM2.5 had a significantly increased risk of developing Lewy body dementia. Interestingly, PM2.5 exposure had a lesser impact on other neurodegenerative diseases not driven by misfolded alpha-synuclein proteins, suggesting a specific connection between air pollution and Lewy body pathology.

To explore the biological mechanisms behind the correlation, the team conducted a series of experiments on mice. Normal mice and genetically modified mice—engineered not to produce alpha-synuclein—were exposed to PM2.5 pollution every other day for 10 months. The results were stark: normal mice developed brain shrinkage, cognitive impairments, and signs of Lewy body-like pathology. In contrast, the genetically modified mice remained largely unaffected, suggesting that air pollution’s toxic effects are specifically mediated through alpha-synuclein.

Further analysis revealed that PM2.5 exposure drove the formation of unusually aggressive and toxic clumps of alpha-synuclein, closely resembling the Lewy bodies seen in human patients. This provided what researchers described as a “mechanistic bridge” between environmental pollution and the biological hallmarks of the disease.

“Putting all of this together, there’s a pretty strong association between air pollution and Lewy body dementia,” said Professor Ted Dawson, a senior author of the study. “We believe air pollution is a significant driving factor, and this needs to be taken seriously in public health policy.”

The research builds on a growing body of evidence linking PM2.5 particles to various forms of cognitive decline, including Alzheimer’s disease. Previous studies have found PM2.5 particles not only in the lungs but also in the bloodstream and even in the brain, where they appear to accelerate neurodegeneration.

In response to these alarming findings, scientists and public health experts are calling for immediate policy action to reduce air pollution levels. Recommended measures include stricter regulations on industrial emissions, transitioning to cleaner transportation methods, improving wildfire management, and limiting residential wood burning.

“Our findings highlight the urgent need for cleaner air policies,” said Dr Mao. “If we can reduce exposure to these harmful pollutants, we may be able to lower the population-wide risk of developing devastating diseases like Lewy body dementia.”

In the UK, researchers at University College London and the Francis Crick Institute have launched a major initiative, the Rapid project (Role of Air Pollution in Dementia), to investigate the broader neurological effects of polluted air. Commenting on the new study, Professor Charles Swanton, a co-leader of the project, described it as an important contribution to the field.

“This is an important and compelling study that deepens our understanding of how air pollution can drive neurodegenerative disease,” said Swanton. “By linking fine-particulate matter exposure to the biology of Lewy body dementia, it provides a crucial mechanistic link between environmental exposure and disease pathology.”

As air pollution continues to be a major global health concern, this new research adds to the mounting evidence that clean air is not only essential for physical health but also for protecting the brain against some of the most devastating forms of dementia.