Non-optimal temperature and ischemic heart disease burden in Hangzhou, China mortality, years of life lost, and subtype-specific patterns

Background Mortality counts do not reflect age at death, and it remains unclear whether mortality and years of life lost (YLL) identify the same high-risk temperatures, lag windows, and ischemic heart disease (IHD) subtypes. We examined these patterns for overall IHD, acute myocardial infarction (AMI), and chronic IHD. Methods We conducted a population-based time-series study in Hangzhou, China, during 2014–2021. Distributed lag nonlinear models were used to estimate temperature associations with daily mortality and YLL. Attributable burden was partitioned into moderate and extreme cold and heat. Results Across 2,922 days, 37,919 IHD deaths and 566,166.3 YLL were recorded. Cold effects were delayed and accumulated over longer lags, whereas heat effects were concentrated within the first week. For overall IHD, extreme-cold relative risks were 1.97 (95% CI 1.42–2.73) for mortality and 1.93 (1.33–2.79) for YLL over lag 0–21 days; corresponding extreme-heat estimates over lag 0–7 days were 1.36 (1.22–1.52) and 1.33 (1.17–1.52). AMI and chronic IHD showed similar lag patterns. Temperatures below the minimum-risk temperature accounted for 17.46% of IHD deaths, and moderate cold contributed about 95% of the cold-attributable mortality estimate. Conclusions Mortality and YLL provided complementary perspectives on temperature-related IHD burden. Although thermal extremes had the highest relative risks, frequent moderate cold accounted for most cold-attributable mortality, supporting distinct prevention windows for heat and cold.