Extreme Heat Exposure and Mortality from Cardiovascular and Respiratory Diseases in Low- and Middle-Income Countries: A Two-Stage Time-Series Analysis and Future Burden Projection

Abstract

Background: Climate change-driven extreme heat is a growing threat to non-communicable disease burden, yet robust multi-country evidence from low- and middle-income countries (LMICs) remains limited despite high vulnerability. Methods: We performed a two-stage time-series analysis across 128 cities in 32 LMICs (2000–2020). Daily CVD (ICD-10 I00–I99) and respiratory (J00–J99) mortality counts were obtained from the Global Burden of Disease Study and WHO Mortality Database; daily mean temperature from ERA5 reanalysis; and socioeconomic/adaptation indicators from World Bank Open Data. Stage 1 used city-specific quasi-Poisson distributed lag non-linear models (DLNMs) adjusted for long-term trends, seasonality, day of week, and holidays. Heatwaves were defined multi-dimensionally by intensity (excess above 95th percentile), duration (≥3 consecutive days), and frequency. Stage 2 pooled estimates via multivariate random-effects meta-analysis and meta-regression, incorporating GDP per capita, health expenditure (% GDP), air-conditioning prevalence, urban/rural status, age (<18, 18–64, ≥65 years), sex, and urban/rural residence. Attributable fractions used the minimum mortality temperature (MMT). Future burdens (2030–2050) were projected under CMIP6 SSP1-2.6, SSP2-4.5, and SSP5-8.5 scenarios using downscaled temperature projections and GBD demographic forecasts. Results: The pooled minimum mortality temperature (MMT) across all 128 cities was 22.4°C. Each 1°C rise above MMT increased CVD mortality by 2.1% (95% CI: 1.8–2.4%) and respiratory mortality by 4.1% (3.7–4.5%), consistent with recent LMIC meta-analyses. Heatwaves raised CVD mortality risk by 14.2% (RR 1.142, 95% CI: 1.118–1.167) and respiratory by 18.7% (RR 1.187, 95% CI: 1.152–1.223), with amplified effects at higher intensity (>3°C excess) and longer duration (≥5 days). Risks were highest among adults ≥65 years (CVD RR 1.28), women, and rural/low-GDP settings. During 2000–2020, heat exposure above MMT accounted for 8.7% of CVD deaths and 11.4% of respiratory deaths across the sampled cities. Projections indicate 162–248% increases in heat-related CVD deaths and 178–271% in respiratory deaths by 2050 under moderate-to-high emissions. Conclusions: Extreme heat disproportionately drives CVD and respiratory mortality in LMICs, modified by socioeconomic and demographic factors. Urgent integration of climate adaptation into chronic disease programs is required.