Air pollution, health system capacity, and non-communicable disease mortality in West Africa: a mediation analysis of the environmental health-healthcare financing nexus

Air pollution is a major contributor to global non-communicable disease (NCD) mortality, yet evidence from West Africa remains limited. We examined the association between ambient PM2.5 air pollution and NCD mortality across West African countries, and investigated whether health system capacity mediates or modifies this relationship. We conducted an ecological panel study using World Bank's World Development Indicators (WDI) data from 11 West African countries (2015–2020; n = 66 country-years). The outcome was the probability of premature NCD mortality (ages 30–70 years) among males. We employed pooled and fixed effects panel regression models, tested effect modification by health expenditure using interaction terms and stratified analyses and assessed mediation using the Baron-Kenny framework with bootstrap confidence intervals. Mean PM2.5 exposure was 60.3 µg/m³ (SD = 14.6), exceeding WHO guideline levels by more than 12-fold. NCD mortality averaged 23.4% (SD = 4.0%). Bivariate analysis indicated an inverse (paradoxical) correlation between PM2.5 and NCD mortality ( r = -0.39, p = 0.001). In pooled models, higher PM2.5 was associated with lower NCD mortality (β = -0.107, 95% CI -0.212 to -0.002); however, this association was eliminated after introducing country fixed effects (β = -0.002, 95% CI -0.035 to 0.030, p = 0.881). Stratified analyses showed significant negative PM2.5-mortality associations only in low health expenditure settings (β = -0.29, p = 0.001), attenuating to null in high expenditure contexts (β = 0.09, p = 0.247). An exploratory mediation analysis found no evidence that health expenditure operated as a statistical pathway in this relationship (indirect effect: 0.001, 95% CI -0.023 to 0.023). The paradoxical ecological association between air pollution and NCD mortality in West Africa reflects substantial confounding by country-level development factors rather than true protective effects. Health system capacity modifies observed associations, highlighting the importance of contextualizing environmental health research within health systems frameworks. Individual-level studies are needed to quantify the true burden of air pollution on NCDs in this region.