Meta analysis of health effects of ambient air pollution exposure in low- and middle-income countries

It is well established that exposure to ambient air pollution affects human health. A majority of literature concentrated on health effects of air pollution in high income countries. Only fewer studies analyzing health effects of air pollution in Low- and Middle-Income Countries (LMICs) are available. To bridge this gap in literature, this study investigated short term and long-term health impacts of ambient air pollutants focussed in LMICs. We evaluated Total Non-accidental mortality, Respiratory Mortality, Stroke Mortality, Cardio-vascular Mortality, Chronic Obstructive Pulmonary Disease (COPD), Ischemic Heart Disease (IHD) and Lung Cancer Mortality in LMICs particularly. Random Effects Model was utilised to derive overall risk estimate. Relative Risk (RR) estimates per 10 μg/m3 was used as input for model. Subgroup and Sensitivity Analysis by Design and Country was conducted. A total of 152 studies were included for quantitative analysis. We found positive associations between pollutants and Total Non-accidental mortality for PM10 ((RR:1.0043-1.0036), p < 0.0001), NO2 (RR:1.0222 (1.0111-1.0336), p < 0.0001), SO2 (RR:1.0107 - (1.0073-1.0140), p < 0.0001), O3 (RR: 1.0038 (1.0023-1.0053), p < 0.0001) and PM2.5 (RR: 1.0048 (1.0037-1.0059), p < 0.0001) for every 10 μg/m3 increase. We found positive association between Long-term exposure to PM10 and Total Non-accidental mortality (RR: 1.0430 (1.0278-1.0583), p < 0.0001) We also found statistically significant positive associations between pollutants and Cardiorespiratory and Cardiovascular morbidity. The positive associations persisted when analysed amongst sub-groups. However, the high heterogeneity amongst studies persisted even after performing sub-group analysis. The study has found statistically significant positive associations between short-term and long-term exposure to Ambient air pollution with various health-outcome combinations.