A rapidly developing evidence base suggests that exposure to outdoor air pollution is a risk factor for the onset of dementia, with an increase in publications in this area since 2022. In 2024 The Lancet Commission on Dementia Prevention, Intervention and Care even identified air pollution as one of 14 modifiable risk factors for dementia.

• Research methodology: The study conducted a systematic review and meta-analysis, searching eight major databases (such as MEDLINE, Embase, Cochrane Library, CINAHL, Global Health, PsycINFO, Scopus, and Web of Science Core Collection) up to 23 October 2023. Primary observational studies of adults (aged ≥18 years) that provided a quantitative analysis of the association between long-term exposure (≥1 year) to outdoor pollutants and subsequent medically diagnosed dementia were included. Of the initial 15,619 records, 51 studies were included in the data extraction. 32 studies that met the criterion of at least three independent studies for a given exposure-outcome pair were selected for meta-analyses.
• Key findings on pollutants and dementia:
  • PM2.5 (fine dust particles): It was detected significant connection between long-term exposure to PM2.5 and incidence of dementia. For 21 studies with a population of 24,030,527 individuals, the pooled adjusted hazard ratio (HR) was 1.08 for every 5 μg/m3 increase in exposure (95% CI 1.02–1.14). This analysis demonstrated significant statistical heterogeneity (I2=95%). Funnel plot asymmetry was observed for PM2.5, suggesting possible publication bias.
  • Nitrogen dioxide (NO2): He was also significantly connected with dementia. For 16 studies with a population of 17,228,429 people, the pooled adjusted HR was 1.03 for each 10 μg/m3 increase in exposure (95% CI 1.01–1.05). Here too, considerable heterogeneity was observed (I2=84%).
  • Black carbon/PM2.5 absorbance: It has been proven significant connectionFor six studies with a population of 19,421,865 people, the pooled adjusted HR was 1.13 for each 1 μg/m3 increase in exposure (95% CI 1.01–1.27). This analysis also had considerable heterogeneity (I2=97%).
  • No significant connection: The study found no significant association for exposure to nitrogen oxides (NOx), PM10 (dust particles with a diameter of up to 10 micrometers), and annual ozone (O3), although this was based on a smaller number of studies.
• Heterogeneity and reliability of evidence: Considerable heterogeneity between studies was observed in most analyses, which may reflect differences in exposure assessment methods, outcome methods, demographic characteristics of populations, and geographic/socioeconomic contexts. The overall certainty of the evidence of the studies in the systematic review was rated as mildMost of the included studies had a probably low to definitely low risk of bias, with only three (9%) of the 32 studies in the meta-analyses having a probably high risk of bias in one of the domains.
• Impacts and benefits: The study findings reinforce and build on existing evidence that long-term exposure to outdoor air pollution is a risk factor for the onset of dementia. Reducing exposure to pollution could reduce dementia rates and Stricter air quality standards would likely bring substantial health, social and economic benefits.

Mechanisms: Several mechanisms, including direct and indirect effects, have been proposed to explain how air pollution may contribute to the development of dementia, often involving the well-established roles of neuroinflammation and oxidative stress. Although this remains an active area of research. Spring