A new large-scale analysis drawing from data on nearly 30 million people has reinforced the link between prolonged exposure to outdoor air pollution and an increased risk of developing dementia. Led by researchers from the Medical Research Council (MRC) Epidemiology Unit at the University of Cambridge, the study found consistent evidence that pollutants from traffic and industrial emissions, especially fine particles and gases, are associated with elevated dementia risk. The findings, published in The Lancet Planetary Health, underscore the growing recognition of environmental factors as important contributors to brain health and cognitive decline.
Dementia, including Alzheimer’s disease, currently affects more than 57 million people globally, and this number is projected to rise to over 150 million by 2050. While some high-income countries have reported slight declines in dementia prevalence, mainly due to improved healthcare and education, much of the world is expected to experience substantial increases in cases. The implications for healthcare systems, caregivers, and societies are profound, making prevention efforts an urgent priority.
To investigate whether air pollution could be one such modifiable risk factor, the researchers conducted a systematic review and meta-analysis of 51 studies, 34 of which were included in a pooled statistical analysis. These studies came from North America, Europe, Asia, and Australia, with most data representing populations in high-income nations. By aggregating the results, the researchers were able to clarify the relationship between pollution exposure and dementia, even in cases where individual studies had conflicting outcomes.
They found significant associations between dementia and three major pollutants: fine particulate matter (PM2.5), nitrogen dioxide (NO₂), and soot. PM2.5, produced by vehicle exhaust, power plants, and industrial activity, was linked to a 17% increase in dementia risk per 10 micrograms per cubic metre (μg/m³). NO₂, another pollutant commonly emitted from diesel engines and gas appliances, was linked to a 3% increase in risk per 10 μg/m³. Soot, a by-product of combustion processes, showed a 13% risk increase for every 1 μg/m³ in concentration.
The biological mechanisms behind these associations are believed to involve inflammation and oxidative stress, both of which are known contributors to neurodegeneration. Pollutants may reach the brain through direct inhalation pathways or by entering the bloodstream from the lungs, leading to widespread inflammation that affects multiple organs, including the brain. These processes are not only implicated in Alzheimer’s disease but also in vascular dementia, which is caused by reduced blood flow to the brain.
The study also highlighted key gaps in the existing literature. Most participants in the analysed studies were white and lived in high-income countries, even though low-income and marginalised communities tend to face greater exposure to pollution. Research has suggested that reducing pollution may provide even greater health benefits in these populations. The authors called for future studies to better reflect global and ethnic diversity to ensure a more equitable understanding and policymaking.
Lead researcher Dr Haneen Khreis stressed that reducing air pollution could offer broad benefits, not just for dementia prevention, but also for public health, social well-being, and climate. Co-author Clare Rogowski added that stricter regulations on emissions from transportation and industry are likely to be necessary. Both emphasised the urgency of coordinated action at regional, national, and global levels to reduce pollutant exposure and the long-term health burden it creates.
In closing, co-author Dr Christiaan Bredell argued that tackling dementia requires a comprehensive, interdisciplinary strategy. This includes not just advancements in medical research and healthcare, but also proactive changes in urban planning, environmental policy, and transportation infrastructure. The evidence presented in this study strengthens the case for treating air pollution as a key modifiable risk factor in the global fight against dementia.
More information: Clare Rogowski et al, Long-term air pollution exposure and incident dementia: a systematic review and meta-analysis, The Lancet Planetary Health. DOI: 10.1016/S2542-5196(25)00118-4
Journal information: The Lancet Planetary Health Provided by University of Cambridge
