Background: Many studies have reported the association between ambient temperature and mortality from cardiovascular disease (CVD). However, the health effects of humidity are still unclear, much less the combined effects of temperature and humidity. In this study, we used humidex to quantify the effect of temperature and humidity combined on CVD mortality. Methods: Daily meteorological, air pollution, and CVD mortality data were collected in four cities in southwest China. We used a distributed lag non-linear model (DLNM) in the first stage to assess the exposure–response association between humidex and city-specific CVD mortality. A multivariate meta-analysis was conducted in the second stage to pool these effects at the overall level. To evaluate the mortality burden of high and low humidex, we determined the attributable fraction (AF). According to the abovementioned processes, stratified analyses were conducted based on various demographic factors. Results: Humidex and the CVD exposure–response curve showed an inverted “J” shape, the minimum mortality humidex (MMH) was 31.7 (77th percentile), and the cumulative relative risk (CRR) was 2.27 (95% confidence interval [CI], 1.76–2.91). At extremely high and low humidex, CRRs were 1.19 (95% CI, 0.98–1.44) and 2.52 (95% CI, 1.88–3.38), respectively. The burden of CVD mortality attributed to non-optimal humidex was 21.59% (95% empirical CI [eCI], 18.12–24.59%), most of which was due to low humidex, with an AF of 20.16% (95% eCI, 16.72–23.23%). Conclusions: Low humidex could significantly increase the risk of CVD mortality, and vulnerability to humidex differed across populations with different demographic characteristics. The elderly (> 64 years old), unmarried people, and those with a limited level of education (1–9 years) were especially susceptible to low humidex. Therefore, humidex is appropriate as a predictor in a CVD early-warning system.

Background: With the global increase in extreme weather events, understanding the effects of consecutive extreme PM _2.5 (EPM) and cold spells (CS) events on specific mortality is vital. Methods: Daily meteorological, air pollution, and mortality data were collected in Zigong. Using the Distributed Lag Nonlinear Model (DLNM), we defined the lag as 14 days and quantified the risk effect of EPM-CS events (P ₉₅ for EPM, P _7.5 for CS) on resident mortality and explored the potential amplification of damage resulting from different patterns of sequential extreme events. Additionally, we calculated the attributable fraction (AF) of extreme events and conducted stratified analyses based on age, gender, marital status, etc. Results: Exposure to cold spells, PM _2.5 , and compound events was statistically associated with an increased risk of mortality. The cumulative rate ratios (CRRs) of EPM-CS events for total non-accidental mortality was 1.56(1.44,1.69). The mortality risks of EPM-CS events in females, elderly people ≥ 65 years, low level of education, and widowed, divorced, and never married were higher, with AF were 6.64%(95%CI: 5.42%, 7.89%),6.51%(95%CI: 5.52%, 7.51%), 6.10%(95%CI: 5.17%, 7.06%) and 7.73%(95%CI: 6.07%, 8.51%), respectively. The attributable fraction of specific mortality due to the EPM-CS events was the highest for cerebrovascular disease. Exposure to combined events was associated with a substantial increase in mortality risk, and the damaging effect of combined events occurring in the short term was more significant. Conclusion: Our findings demonstrated synergistic mortality risks from compound cold and pollution exposure, highlighting a disproportionate impact on vulnerable populations. This evidence supports the rationale for developing integrated early warning systems as a targeted intervention.