Short-term exposure to periods of intense cold, ambient temperatures lower than usual or higher than usual may increase the risk of hospitalization for heart failure, according to an international study based on data from 482,000 hospitalizations in Sweden. The investigation, however, did not find an association between heat waves and the risk of hospitalization for this condition.
Published in the journal JACC and presented simultaneously at the European Society of Cardiology (ESC) Congress 2026, the study analyzed records of heart failure hospitalizations in Sweden between 2006 and 2021. The researchers sought to understand how different levels of temperature and episodes of extreme cold and heat could be related to the worsening of the disease.
Cold periods were defined as two or more consecutive days with daily temperatures equal to or below the 5th percentile of temperatures recorded between October and March. Heat waves corresponded to temperatures equal to or above the 95th percentile between April and September, taking into account the characteristics of each municipality.
The results show that cold periods were associated with a higher risk of hospitalization for heart failure between two and six days after exposure, with a statistically significant association between the third and fifth day. Exposure to lower ambient temperatures was also related to an increased risk of hospitalization between three and six days later, with greater statistical significance between the third and fifth day.
On the other hand, exposure to higher temperatures was associated with an increased risk of heart failure within zero to three days following. No association was identified between exposure to heat waves and hospitalization for heart failure.
“To our knowledge, no previous study has examined the short-term associations between extreme temperature events (cold periods and heat waves) or non-ideal continuous ambient temperatures and hospitalizations for heart failure in a Nordic population,” says Wenli Ni, the study’s lead author and a postdoctoral researcher at the Center for Climate, Health, and the Global Environment at Harvard T.H. Chan School of Public Health.
“This represents a critical knowledge gap, given that high-latitude regions, such as Sweden, are characterized by frequent exposure to cold, while facing emerging and unacclimated vulnerability to heat as global warming progresses,” she adds.
According to the authors, the difference between the delayed risk observed after cold exposure and the more immediate effect associated with higher temperatures underscores the importance of time-sensitive, temperature-tailored responses. Among the measures suggested are intensified monitoring after cold alerts and more urgent responses during heat periods.
In an editorial accompanying the study, Tiantian Li, Deputy Director of the National Institute of Environmental Health, of the Chinese Center for Disease Control and Prevention, in Beijing, argues that the relationship between meteorological conditions and cardiovascular health can no longer be ignored.
“We can no longer practice cardiovascular medicine in a meteorological vacuum,” she says.
“The evidence linking non-ideal temperatures with cardiovascular damage is now substantial. The scientific mission can no longer be limited to accumulating more epidemiological associations; it is time to translate these robust data into an actionable early warning capability,” argues the researcher.
