Heat exposure and its impact on COPD morbidity and mortality: a systematic review and meta-analysis.

Heat exposure is associated with adverse chronic obstructive pulmonary disease (COPD) outcomes, but findings vary across studies. We quantified the heat-COPD association and evaluated sources of heterogeneity. PubMed, Embase, and Google Scholar were searched for observational studies on heat exposure and COPD morbidity or mortality. Random-effects meta-analyses pooled risk estimates, using a three-level model for non-independent estimates. Stratified analyses examined outcome types, heat definitions, lag durations, air-pollution adjustment, geographic scope, and effect-size measures. Thirty-six studies were included. Heat exposure was associated with increased overall COPD risk (pooled risk ratio [RR], 1.15; 95% CI: 1.09-1.21). The association was stronger for mortality (RR, 1.26; 95% CI: 1.18-1.34) than morbidity (RR, 1.05; 95% CI: 1.01-1.09). Heat-wave and threshold-based definitions showed higher pooled associations (both RR, 1.21) than continuous temperature-based definitions (RR, 1.05), which showed lower heterogeneity. Positive pooled associations were observed across the reported lag windows. Air-pollution adjustment did not substantially alter associations. Heat exposure was associated with increased COPD risk, particularly mortality. The magnitude of the association varied by heat-exposure definition, highlighting the need for standardized reporting of heat metrics, thresholds, lag structures, and co-exposures to inform targeted prevention strategies.