Ambient air pollution and type 2 diabetes mellitus: an updated global systematic review, meta-analysis, and cross-country comparative analysis

This study integrated systematic review, meta-analysis, and cross-country ecological comparisons to evaluate associations between ambient air pollutants and T2DM prevalence and incidence. Observational studies published between 2010 and 2025 were analyzed. Meta-analyses included subgroup analyses by geographic region and age group, while cross-country analysis contextualized regional differences in T2DM burden. All pooled estimates are expressed per 10 µg/m³ increase in pollutant concentration. PM₂.₅ exposure was significantly associated with T2DM prevalence (OR = 1.08; 95% CI: 1.06–1.11) and incidence (HR = 1.42; 95% CI: 1.31–1.55). NO₂ showed significant associations with prevalence (OR = 1.27; 95% CI: 1.15–1.40) and incidence (HR = 1.16; 95% CI: 1.09–1.23). PM₁₀ was also significantly associated with prevalence (OR = 1.09; 95% CI: 1.04–1.15) and incidence (HR = 1.79; 95% CI: 1.14–2.83). O₃ was significantly associated with incidence (HR = 1.06; 95% CI: 1.01–1.12), but not prevalence (OR = 1.03; 95% CI: 0.99–1.08). Subgroup analyses showed stronger associations among older adults and Asian populations. Cross-country comparisons showed inverse ecological correlations between T2DM prevalence and environmental performance, food security, education, healthcare expenditure, diabetes treatment coverage, and walkability. Overall, PM₂.₅, NO₂, and PM₁₀ were positively associated with T2DM prevalence and incidence, while O₃ findings were less consistent. The strongest and most consistent evidence was observed for PM₂.₅.