Cold Spells, Heat Waves Raise Heart Failure Risk

In an interview with Pharmacy Times, Petter Ljungman, MD, PhD, a principal researcher at the Karolinska Institute and a senior consultant of cardiology at the Department of Cardiology at Danderyd Hospital in Stockholm, discussed a nationwide Swedish study examining how short-term temperature exposure relates to heart failure (HF) hospitalization.¹

The study, presented at the European Society of Cardiology (ESC) Congress 2026 and published in JACC, used a time-stratified case-crossover design to analyze roughly 482,000 HF hospitalizations recorded in the Swedish National Patient Register between 2006 and 2021. Investigators found that cold spells and lower ambient temperatures were associated with a higher risk of HF hospitalization, with effects delayed by several days, while higher temperatures during the warm season were associated with more immediate increases in risk.¹

Ljungman explained that temperature affects health regardless of climate, because susceptibility depends on the environment people are adapted to—their buildings, behaviors, and clothing—so heat can harm vulnerable individuals even in a country like Sweden. He noted that the study was not mechanistic and could not explain why cold effects were slower than heat effects but suggested the 2 likely act through different physiological pathways.

For pharmacists and other health care providers, Ljungman emphasized that heat effects can be expected early in a heat wave while cold effects arrive later, which should shape patient monitoring, follow-up, and surge-capacity planning. He also addressed the observation that patients taking diuretics appeared more susceptible to heat, cautioning that medications were not randomly assigned and the finding could reflect indication bias. Still, because diuretics affect fluid and salt balance, he advised providers to be careful with these vulnerable patients and to weigh scaling back diuretic use and balancing fluid intake during extreme heat episodes.

REFERENCES

1. Ni W, Agewall S, Benson L, et al. Cold spells, heat waves, and nonoptimal air temperature and risk of heart failure hospitalization in Sweden. J Am Coll Cardiol. 2026;88(9). doi:10.1016/j.jacc.2026.07.008