A COMPREHENSIVE new analysis has strengthened the evidence that long-term exposure to outdoor air pollution significantly increases the risk of developing dementia.
Researchers conducted a large-scale systematic review and meta-analysis to evaluate the link between air pollutants and incident dementia, synthesising findings from studies published up to October 2023. They screened over 15,000 records from eight major databases and ultimately included 32 studies in their meta-analysis, focusing on adults aged 18 and over who had experienced long-term (≥1 year) exposure to air pollution prior to a physician-confirmed dementia diagnosis. Only exposure–outcome pairs reported in at least three studies were included in the pooled analysis, using harmonised effect estimates and random-effects models. Risk of bias and publication bias were also rigorously assessed.
The pooled data, which covered over 24 million participants across 21 studies, showed a statistically significant association between increased dementia risk and exposure to fine particulate matter (PM2.5), with a hazard ratio (HR) of 1.08 per 5 µg/m³ increase (95% CI 1.02–1.14; I²=95%). Nitrogen dioxide was also linked to elevated dementia risk (HR 1.03 per 10 µg/m³, 95% CI 1.01–1.05; I²=84%), as was black carbon or PM2.5 absorbance (HR 1.13 per 1 µg/m³, 95% CI 1.01–1.27; I²=97%). In contrast, no significant association was found for nitrogen oxides, PM10, or ozone. While the certainty of evidence was rated as moderate, the studies included were mostly assessed as having a low risk of bias.
This latest synthesis adds weight to the growing body of evidence implicating air pollution as a modifiable environmental risk factor for dementia. The findings support calls for tighter air quality standards as part of public health strategies to reduce the burden of neurodegenerative disease.
Reference
Best Rogowski CB et al. Long-term air pollution exposure and incident dementia: a systematic review and meta-analysis. Lancet Planet Health. 2025; DOI: 10.1016/S2542-5196(25)00118-4.
