Temp extremes raise HF risk Sweden

A study published in _JACC_ and presented at ESC Congress 2026 links short-term exposure to cold spells and high temperatures to increased heart failure hospitalizations in Sweden, with no association found for heat waves.

Study Design and Population

Researchers analyzed 482,000 heart failure hospitalizations recorded in the Swedish National Patient Register between 2006 and 2021. Cold spells were defined as two or more consecutive days with daily temperatures less than or equal to the 5th percentile for October-March, while heat waves were defined as greater than or equal to the 95th percentile for April-September, using municipality-specific temperature distributions.

Key Findings

Cold spells were associated with a higher risk of heart failure hospitalization within two to six days, reaching statistical significance between three and five days. Lower ambient temperature exposure was linked to increased hospitalization risk within three to six days, also significant between three and five days. Higher temperature exposure correlated with higher risk of heart failure over zero to three days. No association was observed between heat wave exposure and heart failure hospitalization.

Expert Commentary

Wenli Ni, Ph.D., lead author and postdoctoral research fellow at the Center for Climate, Health, and the Global Environment at Harvard T.H. Chan School of Public Health, noted that previous research had not examined short-term temperature effects on heart failure hospitalizations in Nordic populations. "This represents a critical knowledge gap, given that high-latitude settings such as Sweden are characterized by frequent cold exposure while simultaneously facing an emerging, unacclimatized vulnerability to heat as the global climate warms," he said.

Tiantian Li, Ph.D., deputy director of the National Institute of Environmental Health at the Chinese Center for Disease Control and Prevention in Beijing, commented that "We can no longer practice cardiovascular medicine in a meteorological vacuum." He added that the evidence linking non-optimal temperature to cardiovascular harm is now substantial and that it is time to translate these robust data into actionable early-warning capabilities.

Implications for Clinical Practice

The delayed risk of hospitalization after cold temperatures and the immediate risk seen with hot temperatures underscore the need for time-sensitive management, including monitoring following cold alerts and more urgent response strategies during heat.

Publication Details

The study, titled "Cold spells, heat waves, and non-optimal air temperature and risk of heart failure hospitalization in Sweden," appeared in the _Journal of the American College of Cardiology_ in 2026. DOI: 10.1016/j.jacc.2026.07.008

**Clinical Categories**

Cardiology Common illnesses & Prevention

**Source**

This article is provided by the American College of Cardiology.