This is shown in a study of more than 230,000 heart attacks in Sweden, based on SWEDEHEART, a registry funded by the Swedish Heart-Lung Foundation. Another study shows that cold spells can also be associated with an increased risk of death among people with heart failure.

“We see that sudden temperature drops are associated with a higher risk both of having a heart attack and, for those with heart failure, of dying or being admitted to hospital. Dress warmly and be careful if you are going out in the cold, especially if you are older or have cardiovascular disease,” says Stefan Agewall, Professor of Cardiology at Karolinska Institutet.

In a new study, researchers analyzed all heart attacks in Sweden between 2005 and 2019 – a total of 233,617 cases. By linking daily temperature data from the Swedish Meteorological and Hydrological Institute (SMHI) to the patients’ residential areas, the researchers were able to see how rapid temperature changes are associated with an increased risk of hospital admissions for heart attack. The results show that rapid drops in temperature increased the risk of heart attack after 2–3 days. The effect was most pronounced during the colder months of the year, and the risk was slightly higher in men and people with diabetes.

“We see that it is not only extreme cold that can strain the heart, but also how quickly the temperature changes. When the temperature falls rapidly, blood pressure rises and the heart has to work harder, which may help trigger a heart attack in people with vulnerable vessels,” says Stefan Agewall.

A similar association is seen in people with heart failure. In another study, published in the prestigious journal JAMA, the risk of death increased at both unusually low and unusually high temperatures. The effect was greatest in cold conditions. The study included just over 250,000 people with heart failure who died between 2006 and 2021. Those particularly at risk were men, people with diabetes, and people using diuretic medications. Both studies show small but statistically significant associations, not causal relationships, but they indicate that temperature fluctuations may entail increased risk for vulnerable groups.

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Effects of climate change on health

The impact of heat due to climate change is becoming increasingly evident even in the Nordic countries. Heat is a significant cause of mortality among vulnerable groups and risks are further amplified by exposure to air pollution. It is thus crucial that cities be adapted to mitigate this phenomenon and adaptations made must benefit everyone, regardless of socioeconomic status.


“This research shows that the heart can be affected more than many people think when the temperature suddenly drops, especially in older people and those with cardiovascular disease. Take extra care if you are going out in the cold to shovel snow. Dress warmly, avoid sudden strenuous activity, and pay attention to how you are feeling,” says Kristina Sparreljung, Secretary General of the Swedish Heart-Lung Foundation.

Source: Hjärt-Lungfonden