This scoping review included 76 Southeast Asian studies published since 2000: 28 mortality, 38 morbidity and 10 effect-modification studies. Minimum-risk temperatures and thresholds varied widely by location and outcome. Reported relative risks ranged from 1.02 for all-cause admission in Vietnam to 4.21 for dengue in Laos, but these outcomes are not directly comparable. Relationships were often nonlinear, evidence for heat-air pollution synergy was mixed, immediate effects were stronger for NCDs, and some dengue studies reported long lags.
Key findings
- Heat related to mortality and morbidity but thresholds varied; several nonlinear shapes were reported; pollution synergy was inconsistent; vulnerable groups included extreme ages, preexisting respiratory disease, outdoor workers and polluted, crowded or rural communities.
Why this matters globally
The findings support ASEAN heat-health action plans, occupational standards and joint heat-pollution warnings, while thresholds must be locally calibrated.
Thai researcher contribution
The Thailand-based Mahidol and MORU team includes Htoo Wai Aung, Wissanupong Kliengchuay, Sarima Niampradit, Paweena Aendo, Thant Sin Aye, Siriphat Intrakun, Dumrongkiet Arthan, Khuanchai Koompapong and Kraichat Tantrakarnapa.
Limitations to consider
A scoping review maps evidence rather than pooling effects. Definitions, exposure, lag, outcomes and confounding differ; cross-outcome RRs are not comparable; local-language studies may be missed; and long dengue lags may reflect seasonality and vector ecology rather than direct heat effects.