Figure 1
PRISMA flow chart.
Table 1
Baseline characteristics of included studies.
| AUTHOR | YEAR | COUNTRY | DATA SOURCE | DURATION | DESIGN | OUTCOME | POLLUTANTS | EXPOSURE ASSESSMENT | ROB ASSESSMENT |
|---|---|---|---|---|---|---|---|---|---|
| (63) (*) | 2017 | Iran | Iran statistical centre | Short term | Cross-sectional | admission | SO2 | Ground monitoring stations | Low |
| (64) (*) | 2017 | Iran | Hospital database | Short term | Cross-sectional | admission | SO2, NO2, NO, NOx, CO, O3, PM10 | Ground monitoring stations | Average |
| (33) (*) | 2019 | Iran | Hospital database | Short term | Time series | admission | NO2, NO, O3 | Ground monitoring stations | Good |
| (65) (*) | 2005 | Iran | Hospital database | Long term | Time series | admission | SO2, NO2, CO, O3, PM10 | Ground monitoring stations | Good |
| (66) | 2022 | Vietnam | Hospital database | Short term | Time series | admission | PM10, NO2 | Ground monitoring stations | Average |
| (37) (*) | 2016 | Vietnam | Hospital database | Short term | Time series | admission | NO2, PM10, SO2 | Ground monitoring stations | Average |
| (67) (*) | 2017 | Iran | Hospital database | Short term | Time series | admission | SO2, CO2, NO2, O3, PM2.5, PM10 | Ground monitoring stations | Good |
| (32) (*) | 2023 | Iran | Clinical registry | Short term | Time series | admission | CO | Ground monitoring stations | Good |
| (34) (*) | 2019 | Iran | Hospital database | Short term | Case crossover | admission | O3, SO2, NO2, CO, PM10, PM2.5 | Ground monitoring stations | Average |
| (68) | 2022 | Indonesia | Survey data | Long term | Cross-sectional | admission | PM2.5 | Satellite monitoring | Low |
| (38) (*) | 2019 | Bangladesh | Hospital database | Short term | Case crossover | admission | PM2.5 | Ground monitoring stations | Average |
| (35) (*) | 2023 | Iran | Hospital database | Short term | Case crossover | admission | PM2.5, PM10 | Ground monitoring stations | Average |
| (69) | 2017 | Iran | Hospital database | Short term | HIA, WHO AirQ | mortality | O3 | Ground monitoring stations | Low |
| (70) | 2015 | Iran | WHO AirQ | Short term | HIA, WHO AirQ | mortality | O3 | Ground monitoring stations | Low |
| (39) (*) | 2021 | Bangladesh | Hospital database | Short term | Time series | mortality, admission | PM2.5 | Ground monitoring stations | Average |
| (71) | 2017 | Iran | WHO AirQ | Short term | HIA, WHO AirQ | mortality | PM2.5, PM10 | Ground monitoring stations | Low |
| (72) | 2016 | Iran | WHO AirQ | Short term | HIA, WHO AirQ | mortality | PM2.5 | Ground monitoring stations | Low |
| (73) | 2020 | Iran | WHO AirQ | Long term | HIA, WHO AirQ | mortality | PM2.5 | Ground monitoring stations | Low |
| (36) (*) | 2019 | Iran | Hospital database | Short term | Case crossover | admission | PM2.5, PM10, SO2, O3 CO, NO2 | Ground monitoring stations | Average |
| (28) (*) | 2019 | France, Iran, Italy | WHO AirQ | Short term | HIA, WHO AirQ | mortality, admission | PM10, PM2.5, O3 | Ground monitoring stations | Low |
| (74) (*) | 2023 | Iran | Hospital database | Short term | Time series | admission | O3, CO, NO2, SO2, PM10, PM2.5 | Ground monitoring stations | Average |
| (75) (*) | 2022 | Iran | Hospital database | Short term | Time series | admission, mortality | SO2, NO2, CO, O3 | Ground monitoring stations | Good |
| (76) | 2021 | Iran | Hospital database | Short term | Time series | admission | CO, O3, PM2.5, NO2, SO2 | Ground monitoring stations | Good |
| (77) (*) | 2012 | Iran | Hospital database | Short term | Cross-sectional | admission | SO2, CO, NO | Ground monitoring stations | Average |
| (30) (*) | 2021 | Iran | WHO AirQ | Long term | Time series | mortality | PM2.5 | Ground monitoring stations | Low |
| (78) | 2018 | Iran | WHO AirQ | Short term | HIA, WHO AirQ | mortality | PM10, PM2.5 | Ground monitoring stations | Low |
| (79) | 2020 | Vietnam | Hospital database | Short term | Case crossover | admission | PM10, PM2.5, SO2, CO, NO | Ground monitoring stations | Good |
| (80) | 2016 | Iran | WHO AirQ | Short term | HIA, WHO AirQ | mortality | PM10, NO2, O3 | Ground monitoring stations | Low |
| (81) | 2019 | Iran | Municipal records | Long term | Cost analysis | mortality | PM2.5 | Ground monitoring stations | Low |
| (82) | 2014 | Iran | WHO AirQ | Short term | HIA, WHO AirQ | admission | PM10 | Ground monitoring stations | Average |
| (83) | 2022 | Iran | WHO AirQ | Short term | HIA, WHO AirQ | Mortality, admission | PM2.5, PM10 | Ground monitoring stations | Low |
| (84) | 2017 | Iran | WHO AirQ | Short term | HIA, WHO AirQ | mortality | PM10 | Ground monitoring stations | Low |
| (85) (*) | 2018 | Iran | Hospital database | Short term | Ecological | mortality | PM10, O3, NO2, SO2, CO | Ground monitoring stations | Good |
| (86) | 2024 | Bangladesh | Registry data | Long term | Cohort | mortality | PM2.5 | Satellite monitoring | Average |
| (87) | 2021 | Iran | Cohort data | Long term | Cohort | mortality | PM2.5 | Satellite monitoring | Average |
| (88) | 2015 | Iran | National registry | Short term | Cross-sectional | mortality | O3, CO, NO2, SO2, PM10 | Ground monitoring stations | Average |
| (89) | 2018 | Iran | WHO AirQ | Short term | HIA, WHO AirQ | mortality, admission | O3 | Ground monitoring stations | Low |
| (90) | 2016 | Iran | WHO AirQ | Short term | HIA, WHO AirQ | mortality | SO2, NO2 | Ground monitoring stations | Low |
| (91) | 2022 | India | Survey/registry data | Long term | Cohort | mortality | PM2.5 | Ground monitoring stations | Good |
| (92) | 2017 | Iran | Registry data | Long term | Comparative risk assessment | mortality | PM2.5 | Ground monitoring stations | Average |
| (93) | 2017 | Nepal | Hospital database | Short term | Case crossover | admission | PM10 | Ground monitoring stations | Good |
| (94) | 2020 | Iran | Hospital database | Short term | Time series | admission | CO, O3, SO2, NO2, PM10 | Ground monitoring stations | Good |
| (29) (*) | 2021 | Iran | Hospital database | Short term | Time series | admission | PM2.5 | Ground monitoring stations | Average |
| (31) (*) | 2019 | Iran | Hospital database | Short term | Time series | admission | PM10, O3, NO2 | Ground monitoring stations | Average |
| (40) (*) | 2015 | Lebanon | Hospital database | Short term | Time series | admission | PM2.5, PM10 | Ground monitoring stations | Good |
| (95) | 2024 | Iran | WHO AirQ | Short term | HIA, WHO AirQ | mortality | NO2, O3, SO2 | Ground monitoring stations | Low |
| (96) (*) | 2018 | Iran | Hospital database | Short term | Case crossover | admission | CO, O3, NO2, PM10, SO2 | Ground monitoring stations | Good |
| (97) | 2020 | Iran | Municipal records | Short term | Time series | mortality | PM2.5 | Ground monitoring stations | Good |
[i] Note: (*) studies included in the meta-analysis, Air quality modelling software (WHO AirQ). WHO, World Health Organization; HIA, Health Impact Assessment; AirQ, Air Quality Health Impact Assessment tool.
Table 2
Meta-Analysis results.
| CATEGORY | RR | 95% CI LOWER | 95% CI UPPER | NUMBER OF STUDIES | NUMBER OF DATA POINTS | I2 |
|---|---|---|---|---|---|---|
| CO | ||||||
| mortality + admission | 1.0001 | 1.0001 | 1.0001 | 12 | 14 | 84.8% |
| admission | 1.0001 | 1.0001 | 1.0001 | 11 | 13 | 86.0% |
| mortality | – | – | – | – | – | – |
| NO2 | ||||||
| mortality + admission | 1.0066 | 1.0036 | 1.0097 | 12 | 15 | 56.1% |
| admission | 1.0062 | 1.0026 | 1.0099 | 11 | 13 | 51.0% |
| mortality | 1.0108 | 1.0008 | 1.021 | 2 | 2 | 85.0% |
| NO | ||||||
| mortality + admission | ||||||
| admission | 1.002 | 0.9987 | 1.0053 | 3 | 3 | 28.5% |
| mortality | – | – | – | – | – | – |
| O3 | ||||||
| mortality + admission | 0.9995 | 0.9988 | 1.0002 | 12 | 15 | 84.3% |
| admission | 0.999 | 0.9985 | 0.9995 | 10 | 12 | 83.5% |
| mortality | 1.0038 | 1.0007 | 1.0069 | 3 | 3 | 47.7% |
| PM10 | ||||||
| mortality + admission | 1.0168 | 1.0017 | 1.0321 | 13 | 19 | 88.1% |
| admission | 1.0191 | 1.0017 | 1.0368 | 12 | 17 | 87.2% |
| mortality | 1.0032 | 0.9984 | 1.008 | 2 | 2 | 95.1% |
| PM2.5 | ||||||
| mortality + admission | 1.0053 | 1.0031 | 1.0075 | 12 | 18 | 74.3% |
| admission | 1.0046 | 1.0025 | 1.0067 | 11 | 15 | 72.1% |
| mortality | 1.0384 | 0.9813 | 1.0988 | 3 | 3 | 86.8% |
| SO2 | ||||||
| mortality + admission | 1.0015 | 0.9986 | 1.0044 | 13 | 16 | 34.4% |
| admission | 1.0022 | 0.9991 | 1.0053 | 12 | 14 | 34.3% |
| mortality | 0.9976 | 0.9909 | 1.0044 | 2 | 2 | 25.6% |
Figure 2
Forest plot of pooled relative risks for cardiovascular outcomes (per 10 µg/m3 increment).