Exposure to extreme cold and high temperatures can increase the risk of hospitalisation among people with heart failure, a large Swedish study has found.
The study, published in the Journal of the American College of Cardiology (JACC) and presented at the 2026 European Society of Cardiology Congress, found that short periods of extreme cold were followed by a higher risk of heart failure hospitalisation, while exposure to higher temperatures was associated with an increased risk within a shorter period.
The findings highlight the potential impact of temperature extremes on people living with heart failure and the need for health systems to prepare for weather-related health emergencies.
Researchers analysed about 482,000 heart failure hospitalisations recorded in the Swedish National Patient Register between 2006 and 2021.
They examined the effects of cold spells, heat waves and daily temperatures that were outside the optimal range for health.
Cold spells were defined as at least two consecutive days when temperatures fell at or below the fifth percentile for the local area between October and March.
The researchers found that cold spells were associated with a higher risk of heart failure hospitalisation within two to six days of exposure, with the strongest statistically significant association occurring between three and five days.
Lower ambient temperatures also increased the risk of hospitalisation, particularly three to five days after exposure.
Higher temperatures, however, were linked to a more immediate increase in heart failure risk, occurring within zero to three days of exposure.
Interestingly, the researchers found no statistically significant association between heat waves and heart failure hospitalisation.
Heat waves were defined as two or more days with temperatures at or above the 95th percentile for the local area between April and September.
Lead author Dr Wenli Ni, a postdoctoral research fellow at the Harvard T.H. Chan School of Public Health, said the findings addressed an important gap in understanding how temperature affects heart failure in Nordic populations.
“High-latitude settings such as Sweden are characterised by frequent cold exposure while simultaneously facing an emerging, unacclimatised vulnerability to heat as the global climate warms,” she said.
According to the researchers, the delayed increase in hospitalisation following cold exposure and the more immediate risk associated with higher temperatures point to the need for time-sensitive measures.
They said patients may require closer monitoring following cold-weather alerts, while heat events may demand faster responses to prevent sudden deterioration.
In an accompanying editorial, Dr Tiantian Li, deputy director of the National Institute of Environmental Health at the Chinese Center for Disease Control and Prevention, said cardiovascular care must increasingly take weather conditions into account.
“We can no longer practise cardiovascular medicine in a meteorological vacuum,” Li said.
She noted that evidence linking unsuitable temperatures to cardiovascular harm is now substantial, adding that research should move beyond simply documenting the association to developing practical early-warning systems.
The researchers said the findings could help health authorities improve preparedness for environmental stressors, particularly as climate change increases exposure to extreme temperatures.
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