Rising Global Temperatures Increase Heat-Related Mortality in Older Patients With Heart Failure

Extreme temperatures were found to exacerbate cardiovascular mortality in older patients with heart failure (HF), according to a new research letter published in JAMA Cardiology.¹ As human biology was evolutionarily designed to function within a narrow range of temperatures, rising temperatures pose a threat to vulnerable populations.

The increase in ambient temperatures can be attributed to rising greenhouse gases (GHGs). Nonoptimal temperatures (NOTs)—deviations from the optimal range—challenge metabolic processes, cardiovascular function, and fluid balance for optimal maintenance.¹ Furthermore, global CO₂ emissions were at an all-time high in 2024 and are expected to grow exponentially with the expansion of fossil fuels and administrative repeals on GHG emissions.^1,2 A proposed ruling, from the Environmental Protection Agency, under the Trump administration, states that “fossil fuel–fired power plants do not contribute significantly to dangerous air pollutants.” However, the agency’s 2024 Annual GHG index reported that the index was 1.51, a nearly 51% increase in the total warming effect since the 1990s.³

The research letter noted how GHGs' influence on rising temperatures negatively impacted outcomes in older patients with HF, as they are particularly sensitive to heat-related effects.¹ Heat-related mortality in persons over the age of 65 has increased by 167% since the 1990s. The study observed a nonlinear relationship between NOTs and adverse health outcomes that, when plotted, resembled a U- or J-shaped figure. The curve, coined as the minimum mortality temperature (MMT), was found to be steeper for extreme cold temperatures compared with extreme hot temperatures.

“The geographic variations in MMT and the adverse health impact of deviations from MMT are likely a reflection of the extent of human acclimatization, encompassing physiological, behavioral, and technological adaptations to local climate,” the research authors wrote.

Geographic Variations in Heat-Related Mortality

The analysis encompassed heat-related premature deaths in 750 locations from 43 countries. Contrary to the assumption, rates of heat wave–related deaths were higher in Eastern and Northern Europe areas that had polar and alpine climates compared with locations in tropical climates.

Lower heat-related death ratios were observed in other parts of Europe with a significant range in temperature, alluding to the idea that persons in areas with polar or alpine climates have less exposure to extreme heat. Therefore, they’re less likely to have physiologically, behaviorally, and infrastructurally adapted to extreme heat, thus increasing the risk of heat-related mortality as global temperatures continue to rise.¹

Surprisingly, data rea lacking on heat-related mortality in countries that regularly experience extreme heat, such as South Asia and the Middle East. Thus, incentivizing a demand for more research observing geographic disparities in NOT-related mortality and cardiovascular outcomes.

Heat-Related Association, Mortality in Heart Failure

Short-term exposure in a time-stratified case-crossover study conducted in Sweden from January 1, 2006, to December 31, 2021, observed a similar U-shaped MMT curve in both all-cause and cardiovascular mortality.⁴ Data on 250,640 patients with HF and a mean age of 84.3 years, collected from the Swedish National Patient Register and the Cause of Death Register, were used in the analysis published in JAMA Network Open.⁴

All-cause mortality ORs were 1.130 (95% CI, 1.074-1.189) for low temperatures and 1.054 (95% CI, 1.017-1.093) for high temperatures over the entire study period. For cardiovascular mortality, low temperatures were associated with an OR of 1.160 (95% CI, 1.083-1.242) over the entire study period, and high temperatures with an OR of 1.084 (95% CI, 1.014-1.159) during 2014-2021.⁴

“These trends were not simply a consequence of climate trends but increasing vulnerability of the population (older, polypharmacy),” the authors explained. “Indeed, Sweden has a rapidly aging population, with more than 20% of the population over the age of 65 years.”¹

The study was limited by the use of outdoor ambient temperatures as proxies since the majority of older patients spent more time indoors. Individual exposure data are also not feasible on a national scale. Ejection fraction data were also absent, thus limiting the researcher’s ability to assess for susceptibility across HF phenotypes.⁴

“Regardless of whether this is driven by climate or demographic trends of an aging global population increasingly burdened with HF,” the research letter authors wrote. “This study importantly provides much-needed evidence for the urgent need for climate adaptation strategies for at-risk older adult populations.”¹

References

1. Rajagopalan S, Brook RD, Deo S. Heart failure and nonoptimal temperatures. JAMA Cardiol. Published online October 22, 2025. doi:10.1001/jamacardio.2025.3939

2. Brady J. Trump’s EPA plans to repeal climate pollution limits on fossil fuel power plants. NPR. June 11, 2025. Accessed October 23, 2025. https://www.npr.org/2025/06/11/nx-s1-5429578/trump-power-plants-epa-climate-change

3. The NOAA annual greenhouse gas index (AGGI). NOAA Global Monitoring Laboratory. Updated Summer 2024. Accessed October 23, 2025. https://gml.noaa.gov/aggi/aggi.html

4. Ni W, Benson L, Ljungman P, et al. Short-term exposure to low and high temperatures and mortality among patients with heart failure in Sweden. JAMA Cardiol. Published online October 22, 2025. doi:10.1001/jamacardio.2025.3932