High and Low Temperature Exposure May Influence Cardiovascular Disease Mortality

Exposure to low and high ambient temperatures may increase mortality risk among patients with heart failure, according to recent research from Harvard’s School of Public Health.1

Cardiovascular disease (CVD) mortality rates have been associated with low and high temperatures in prior research. A 2024 global study highlighted this association, finding that almost 2 million deaths annually were associated with nonoptimal temperatures. Additionally, its global structure enabled it to highlight heterogeneous spatiotemporal patterns.2

“Despite this concern, research on the association between low and high temperature exposures and mortality in patients with heart failure remains limited,” Wenli Ni, PhD, center for climate, health, and the global environment, department of environmental health, Harvard T. H. Chan School of Public Health, and colleagues wrote. “Furthermore, there is a paucity of research exploring how the presence of comorbidities or the use of specific medications might modulate the vulnerability of patients with heart failure to temperature-related mortality.”1

Ni and colleagues conducted this study in Sweden, collecting data from the Swedish National Patient Register, which is linked to the Cause of Death Register and the Dispensed Drug Register through personal identification numbers assigned to all permanent residents of Sweden. All patients with heart failure who died from any cause between 2006 and 2021 were selected.1

The study employed a time-stratified case-crossover design, comparing exposure levels on the day of the death event—the case day—with those on equivalent weekdays—the control days—in the same calendar month and year. The team avoided overlap bias between case and control periods by focusing on exposure windows within a lag period of 0-6 days.1

A total of 250,640 patients were initially included, of whom ≥144,729 deaths were attributed to CVD. The mean age at all-cause death was 84.3 years (standard deviation [SD] 9.4). The mean (SD) range of daily mean air temperature over the period of 2006-2021 was 43.93° F (46.24° F [-30.1°F to 79.3°F]).1

The association between short-term exposure to daily air temperatures and all-cause and CVD mortality exhibited a consistent U-shaped pattern during the entire study period. Investigators noted an elevated mortality risk at both low and high temperature, with a more pronounced association at lower temperatures. Additionally, temporal variation in the exposure-response curves indicated a stronger association from 2014 to 2021 compared to 2006 to 2013.1

All-cause mortality during the entire study period exhibited odds ratios (OR) of 1.13 (95% CI, 1.074 to 1.189) for low temperatures and 1.054 (95% CI, 1.017 to 1.093) for high temperatures. By period, investigators noted low temperature ORs of 1.108 (95% CI, 1.027 to 1.195) in 2006 to 2013 and 1.149 (95% CI, 1.074 to 1.229) in 2014 to 2021. Associations with high temperature were stronger in 2014 to 2021 (OR, 1.082; 95% CI, 1.029 to 1.138) than in 2006-2013 (OR, 1.024; 95% CI, 0.973 to 1.077), although this difference was not statistically significant.1

CVD mortality risk was higher in lower temperatures (OR, 1.16; 95% CI, 1.083 to 1.242) in both subperiods, and high temperatures were not associated with increased CVD mortality overall or during 2006-2013. However, a significant association occurred in 2014 to 2021 (OR, 1.084; 95% CI, 1.014 to 1.159) which was substantially higher than in 2006 to 2013 (OR, 1.001; 95% CI, 0.973 to 1.029).1

“In conclusion, short-term exposure to both low and high temperatures was associated with increased all-cause and CVD mortality risk among patients with heart failure in Sweden,” Ni and colleagues wrote. “The observed rise in mortality risk associated with high temperatures over time underscores the importance of timely adaptation measures, even in high-latitude regions not traditionally considered heat vulnerable.”1

References

1. 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 Cardiology. Published online October 22, 2025. doi:10.1001/jamacardio.2025.3932

2. Hundessa, S, Huang, W, Zhao, Q. et al. Global and Regional Cardiovascular Mortality Attributable to Nonoptimal Temperatures Over Time. JACC. 2024 Jun, 83 (23) 2276–2287. https://doi.org/10.1016/j.jacc.2024.03.425