Ambient Temperature and Heart Failure Hospitalizations in Older Adults in the US

Importance: The U-shaped association between ambient temperature and cardiovascular mortality is well established. However, limited knowledge exists about the association between ambient temperature and heart failure (HF) hospitalizations, particularly among older adults in the US. Understanding this association is essential to informing climate adaptation strategies and health policies. Objective: To assess the association between daily ambient temperature exposure and HF hospitalization among Medicare beneficiaries both nationally and by climate region. Design, Setting, and Participants: This time-stratified case-crossover study included older adults (aged ≥65 years) hospitalized for HF between January 1, 2007, and December 31, 2022, based on Medicare claims data. Cases were defined as emergency department visits leading to HF hospitalization with up to 4 controls, or nonevent days, matched for the same patient on day of week, month, and year. The data analysis was performed between June 2025 and August 2026. Exposure: Daily mean ambient temperature derived from the Parameter-Elevation Relationships on Independent Slopes Model linked through residential zip code. Main Outcomes and Measures: The association between mean temperature exposure and HF hospitalization was estimated nationally and by 9 climate regions (Central, East North Central, Northeast, Northwest, South, Southeast, Southwest, West, West North Central) using conditional logit for distributed lag nonlinear models (reference, 75 °F). A 14-day lag was used for mean temperatures less than 75 °F and 0-day lag for mean temperatures greater than 75 °F. Results: A total of 1 517 756 HF hospitalizations from 996 312 patients (mean [SD] age, 78.0 [8.2] years, 60.3% female) were identified. Colder ambient temperatures were associated with increased HF hospitalizations nationally. At the regional fifth percentile temperature compared with 75 °F, the largest associations were observed in the West North Central (n = 17 286 [1.1%]; odds ratio [OR], 1.62; 95% CI, 1.25-2.11), West (n = 107 911 [7.1%]; OR, 1.40; 95% CI, 1.28-1.53), Southwest (n = 30 536 [2.0%]; OR, 1.34; 95% CI, 1.11-1.62), and Northwest (n = 33 353 [2.2%]; OR, 1.34; 95% CI, 1.08-1.65) regions. Temperatures greater than 75 °F were not associated with increased HF hospitalization. Conclusions and Relevance: This study found that among Medicare beneficiaries, colder ambient temperatures were associated with increased HF hospitalizations, whereas warmer temperatures were not. The U-shaped temperature-cardiovascular risk association described for cardiovascular mortality and other cardiovascular outcomes did not apply for HF hospitalizations among older adults in the US. These findings suggest that ongoing region-specific surveillance of heat- and cold-related HF hospitalization risk will be essential, particularly in areas with limited adaptive capacity.