A cold day in Budapest might be a warning sign that you can't see with your eyes. Researchers in Hungary studied more than 114,000 heart-related emergencies and found that falling temperatures can predict dangerous spikes in cardiac arrests up to three days in advance. It's a finding that could one day let doctors, families, and rescue teams prepare before the worst happens.
The study, published in the journal Public Health, came from a team at Semmelweis University, the Budapest University of Technology and Economics, and the Hungarian National Ambulance Service. They compared five years of data—from November 2018 to December 2023—on out-of-hospital cardiac arrests (a heart stoppage that happens outside a hospital, often at home or in the street) with daily weather records including temperature, wind, pressure, humidity, and air quality.
Why does this matter? Out-of-hospital cardiac arrest is one of the leading causes of death in wealthy countries. In Europe, it strikes an estimated 67 to 170 people per 100,000 each year, and survival still stays below 10 percent. If forecasters could flag risky days ahead of time, ambulance crews and hospitals could get ready, and the public could be reminded how vital it is to start CPR fast.
The numbers are striking. Every one-degree drop in average temperature was linked to a 1.4 percent increase in the daily number of cardiac arrests. And winter brought nearly 18 percent more of these events than summer. Interestingly, it wasn't only sudden plunges in temperature that mattered—lower temperatures in general raised the risk. Still, rapid changes stood out: a daily drop of more than 5°C could itself act as a warning signal.
One of the most useful insights was timing. Weather effects didn't show up right away. Instead, cardiac arrests could climb as much as three days after the weather changed. That lag is what makes an early warning system possible. The team built a predictive model that takes meteorological data and estimates how many cases to expect nationwide on any given day.
"In a previous study, we examined how extreme cold and heat affect the incidence of out-of-hospital cardiac arrest. This time, we went one step further," said Dr. Endre Zima, professor at the Heart and Vascular Center of Semmelweis University and lead researcher. Dr. Ádám Pál-Jakab, first author and a resident physician at the same center, clarified a key point: the model doesn't guess an individual's risk—instead, it forecasts the total number of cases expected across the whole country.
In the future, a phone alert on a cold morning might quietly remind a person with heart disease to bundle up, take it easy, and make sure loved ones know the signs. For the teams who answer the call, a few days of advance notice could mean the difference between a stretched-thin service and one that's ready. Weather, it turns out, may carry a warning that saves lives.