Association between air pollution, multimorbidity and polypharmacy: a systematic review and meta-analysis.

OBJECTIVES: To comprehensively examine the existing literature investigating the association between air pollution exposure and multimorbidity and/or polypharmacy. DESIGN: Systematic review and meta-analysis. DATA SOURCES: PubMed, Web of Science, EMBASE and the Cochrane Library. ELIGIBILITY CRITERIA: Observational studies assessed the association between air pollution and the risk of multimorbidity and/or polypharmacy among the general population were searched. Only full-text original human studies written in English up to 1 April 2026 were included. DATA EXTRACTION AND SYNTHESIS: Data was extracted using a standardised data extraction template and analysed using Stata SE V.19. Estimates were pooled using a random effects model, with the I 2 statistic used to estimate heterogeneity of results (PROSPERO registration: CRD42024613048). RESULTS: In total, 22 studies met the inclusion criteria in our systematic review and 21 of 22 were included for meta-analysis. After excluding incompatible effect estimates (increment other than per 5 µg/m3, 10 µg/m3 or IQR increase) and studies using overlapping datasets, four, three, two and four were included in the main meta-analysis, respectively, with a pooled adjusted risk ratio (aRR) of 1.15 (95% CI 1.08 to 1.23; I 2 =93.0%) per 5 µg/m³ particulate matter (PM)2.5 increase, a pooled aRR of 1.27 (95% CI 1.11 to 1.47; I 2 =99.5%) per 5 µg/m³ PM10 increase, a pooled aRR of 1.07 (95% CI 1.05 to 1.09; I 2 =0.0%) per 5 µg/m³ PM1 increase and a pooled aRR of 1.12 (95% CI 1.00 to 1.26; I 2 =96.6%) per 5 µg/m³ nitrogen dioxide (NO2) increase. There was no evidence of associations between other air pollutants (nitrogen oxides (N=3), black carbon (N=1), sulphur dioxide (N=3), ozone (N=4), carbon monoxide (N=3)) and multimorbidity. No eligible studies on polypharmacy, indoor air pollution, older adults, American and Oceanian populations were identified. CONCLUSIONS: Long-term exposure to ambient PM2.5 and NO2 may elevate the risk of multimorbidity. Future research should prioritise household air pollution, rural areas, older populations as a target group, continents other than Europe and Asia and polypharmacy.