Heat- and Cold-Related Mortality Burden in the US From 2000 to 2020

Importance: With a warming climate, it is essential to have up-to-date and spatiotemporally resolved quantification of the national mortality burden attributable to nonoptimal temperatures. Objective: To investigate the mortality burden associated with heat and cold in the entire contiguous US from 2000 to 2020. Design, Setting, and Participants: This case series assessed death records from the National Center for Health Statistics for all counties within the contiguous US from January 1, 2000, to December 31, 2020. The study used 2-stage modeling, with the first stage being a case-crossover design with county-specific conditional logistic regression of mortality on daily mean temperature incorporating distributed lag nonlinear models and the second stage pooling the estimates by metaregression. Based on the estimated exposure-response functions for temperature and mortality, attribution analyses for low and high temperatures were performed. Calendar time trends were analyzed, and stratified analyses by cause of death and demographic factors (ie, age, sex, and marital status) were performed. This analysis was conducted from August 9, 2024, to June 16, 2025. Exposures: Daily mean temperature and dewpoint temperature at a 4-km resolution for the contiguous US from the Parameter-Elevation Relationships on Independent Slopes Model (PRISM) climate database. Main Outcomes and Measures: All-cause mortality and 7 specific causes, including endocrine, nutritional and metabolic diseases; mental, behavioral and neurodevelopmental disorders; nervous system diseases; circulatory diseases; respiratory diseases; digestive diseases; and external causes. Results: A total of 54 223 429 deceased individuals were included in the analyses. Most decedents were 65 years or older (73.4%); 50.2% were male, 37.4% were married, and 35.1% were widowed. Both low and high temperatures were associated with increased odds of death within 0 to 6 days. Compared with the minimum mortality temperature, temperatures at the 5th and 95th percentiles were associated with odds ratios (ORs) of 1.057 (95% CI, 1.051-1.064) and 1.011 (95% CI, 1.009-1.013), respectively. The excess annual deaths attributable to low and high temperatures were estimated to be 45 992 (95% CI, 28 639-63 202) and 3414 (95% CI, 1650-5173), respectively, with regional variations and an increase in the high temperature burden from 2670 annual deaths during the 2000-2009 period to 4091 during the 2010-2020 period. Heterogeneity existed by cause of death, age, sex, and marital status. Conclusions and Relevance: In this case series, nonoptimal temperatures were critical environmental contributors associated with mortality burden, with differential vulnerability by geographic location, cause of death, and demographic factors. These findings highlight the need for urgent actions against temperature-related health burdens through tailored climate and public health strategies, considering the local context and demographic profiles.