The association between monthly ambient temperatures and ischemic heart disease mortality in the United States: A nationwide ecological analysis, 1999–2020

Ischemic heart disease (IHD) is the leading cause of death in the United States, but the long-term impact of ambient temperature on IHD mortality remains poorly characterized. Existing research has largely examined short-term temperature extremes. This study is among the first to quantify the association between monthly ambient temperature and IHD mortality across the United States over a 22-year period. In this nationwide ecological study, we examined monthly state-level associations between ambient temperature and IHD mortality from 1999–2020. Mortality data were obtained from CDC WONDER and temperature data from the National Centers for Environmental Information. A negative binomial regression with a distributed lag non-linear model estimated the temperature–mortality relationship, adjusting for state, year, and month fixed effects. Subgroup analyses were conducted by age, sex, race, and climate. A strong inverse association between ambient temperature and IHD mortality was observed (Wald p < 0.001). Colder temperatures were associated with higher mortality risk, whereas warmer temperatures were associated with lower mortality risk at the monthly level. The risk was greatest at the coldest observed temperature (–12.8 °F, RR 1.10, 95% CI: 1.05–1.16) and lowest at the warmest temperature (89.2 °F, RR 0.90, 95% CI: 0.86–0.94), reflecting a 20% difference in relative risk across the observed temperature range. Lag effects were strongest in the month of exposure and attenuated thereafter. The model demonstrated a 93.6% reduction in deviance between null and fully adjusted models. Associations were generally consistent across demographic and climate subgroups, though some estimates were imprecise, likely reflecting smaller event counts. This nationwide ecological analysis identifies a significant inverse association between monthly ambient temperatures and IHD mortality in the U.S. at the population level. These findings highlight ambient temperature as an environmental factor associated with IHD mortality and underscore the need for public health interventions to mitigate cardiovascular mortality during prolonged cold periods.