The impact of extreme temperatures on respiratory mortality in Brazil: Evaluating regional adaptations to different thermal environments

Ambient temperature is associated with respiratory mortality, but evidence from tropical middle-income countries remains limited. We conducted a nationwide ecological time-series study to quantify associations between temperature and respiratory mortality across Brazil's diverse climates and to estimate the attributable burden. We analysed 1,087,094 respiratory deaths (ICD-10 J00–J99) from 646 municipalities (population ≥50,000) spanning all five Brazilian macroregions from 2010 to 2020. Daily temperature-mortality associations were estimated using distributed lag non-linear models (DLNM) with quasi-Poisson regression, adjusting for seasonality, long-term trends, and day of week. City-specific estimates were pooled using random-effects meta-analysis, and attributable fractions were calculated using the minimum mortality temperature (MMT) as reference. The pooled exposure-response curve showed a J-shaped relationship between temperature and respiratory mortality. The national MMT was 22.4°C, with low heterogeneity across municipalities (I² = 17.3%). Cumulative relative risks over lags 0–21 days were 1.29 (95% CI: 1.23–1.35) at the 1st temperature percentile (12.1°C) and 1.43 (95% CI: 1.36–1.50) at the 99th percentile (30.3°C). Overall, 6.08% of respiratory deaths were attributable to non-optimal temperatures, corresponding to 66,079 excess deaths during the study period. Regional patterns varied markedly: the North exhibited heat-dominant vulnerability (attributable fraction 12.5%), whereas the South showed cold-dominant effects (7.5%). Heat exposure accounted for a larger share of the national burden (4.27%) than cold (1.81%), reflecting Brazil's predominantly tropical climate. Temperature extremes substantially increase respiratory mortality across Brazil, with distinct regional vulnerability profiles. These findings support the implementation of region-specific early warning systems addressing both thermal extremes and inform climate adaptation strategies for tropical settings.