Air pollution directly linked to increased dementia risk Date: 04 September 2025 Author: Rachel Fieldhouse --- Summary A large-scale analysis involving 56 million people has demonstrated a direct association between long-term exposure to fine particulate air pollution (PM2.5) and an increased risk of developing Lewy body dementia, which is the third most common type of dementia after Alzheimer’s disease and vascular dementia. Key Findings PM2.5 Exposure and Dementia: Exposure to airborne particles smaller than 2.5 micrometres (PM2.5) accelerates the development of Lewy body dementia and Parkinson’s disease with dementia. PM2.5 exposure does not initiate the disease but speeds up progression in genetically predisposed individuals. Disease Background: Lewy body dementia encompasses Parkinson’s disease with dementia and dementia with Lewy bodies. The condition is characterized by the build-up of α-synuclein (αSyn) protein clumps (Lewy bodies) in brain nerve cells, leading to cell death. Study Details: Data from 2000 to 2014 hospital admissions were analyzed for individuals with Lewy body dementia and Parkinson’s disease, with or without dementia. Findings showed: A 12% increased risk of hospitalization for severe dementia with Lewy bodies associated with long-term PM2.5 exposure. Higher relative risk of Lewy body dementia in areas with greater PM2.5 concentrations compared to Parkinson's without dementia. Experimental Insights Mouse Model Experiments: Mice exposed intranasally to PM2.5 over 10 months displayed: Dementia-like behavioral impairments in spatial memory and object recognition tests. Increased accumulation of αSyn protein in the brain. Shrinkage of the medial temporal lobe, involved in memory formation and retrieval. Genetically modified mice lacking αSyn showed no brain changes, highlighting αSyn's role in neurodegenerative pathology. Clumps of αSyn were also found in the gut and lungs, supporting the idea of αSyn spreading from the gut to the brain via the gut-brain axis. PM2.5 triggered lung inflammation and entered the bloodstream, crossing the blood-brain barrier. Genetic Correlation: Gene expression patterns in PM2.5-exposed mice correlated strongly with those from people with Lewy body dementia and Parkinson’s disease with dementia, but not Parkinson’s without dementia. This emphasizes the requirement of a genetic predisposition for increased dementia risk due to air pollution. Conclusions & Future Directions The study highlights PM2.5 as a significant risk factor accelerating Lewy body dementia in susceptible individuals. Limitations include the mouse exposure model using high doses over shorter timeframes versus low-dose, continuous human exposure. Future work aims to: Develop models better simulating real-world exposure. Investigate which specific PM2.5 molecules contribute to disease development. Further elucidate how air pollution leads to neurodegenerative diseases. --- Visuals Image of motorcyclists covering their faces with cloth masks to protect against pollution in New Delhi. Maps correlating US regional PM2.5 levels with hospital admissions for Parkinson's disease, with and without dementia. --- References Zhang, X. et al. Science 389, eadu4132 (2025). DOI: 10.1126/science.adu4132 Best Rogowski, C. B. et al. Lancet Planet. Health 9, 101266 (2025). DOI: 10.1016/S2542-5196(25)00118-400118-4) Li, T. et al. Innovation 3, 100213 (2022). --- DOI: 10.1038/d41586-025-02844-9