Are cold days most risky for heart attacks?

A tree and a fence covered in snow

News reports have warned of a ‘chilling risk’ of having a heart attack when temperatures drop below freezing, and even when the skies are cloudy and windy. We look behind the headlines.

26 October 2018

The research

New research has found that heart attacks are more likely to happen on days when the air temperature is below freezing.

Scientists from Lund University in Sweden have conducted the largest study to date into the link between different weather conditions and heart attacks. They studied data from more than 274,000 people in Sweden who had heart attacks between 1998 and 2013, and found that heart attacks were more common on colder days, as well as days with lower air pressure, high winds and less sunshine. Colder temperatures were associated with higher heart attack rates in warmer seasons as well as winter.

[They] found that heart attacks were more common on colder days, as well as days with lower air pressure, high winds and less sunshine.

A number of explanations have been put forward to explain the link. The authors of the study suggest the most probable cause is that during cold weather the blood vessels near the skin constrict to conserve the body’s heat, which in turn could put more pressure on the heart and cause fatty plaques inside arteries to rupture and block the blood supply to the heart.

They also note that illnesses such as flu and chest infections are more common during colder weather, and are known to increase a person’s risk of having a heart attack.

Changes in behaviour might also play a role, as people might feel less inclined to exercise and eat healthily during colder months, however the researchers did not collect this information. Lower vitamin D levels may also contribute to the increased risk.

The BHF view

Ashleigh Li, Senior Cardiac Nurse at the BHF, said: “This is one of several studies that points to colder temperatures and less sunshine in the winter months leading to more people having heart attacks.

You obviously can't choose when you have a heart attack, but the seasons shouldn't have such an impact on our heart health.

Ashleigh Li, Senior Cardiac Nurse at the BHF

"You obviously can’t choose when you have a heart attack, but the seasons shouldn’t have such an impact on our heart health. But this doesn’t mean you should stay inside until next spring. We need more research to help us find out why winter months make people more likely to have a heart attack, as well as continuing to do all we can to stop people having heart attacks in the first place.”

How the research was reported

The Guardian, The Sun and The Daily Mail headlines both highlighted the link between cold temperatures and heart attack risk, while The Telegraph headline focussed on wind: “Why windy days could be deadly for people with weak hearts”. When the researchers took into account air pollution levels, however, they found that only air temperature remained significantly associated with heart attack risk. This means that air pollution may explain some of the risk seen with other weather conditions such as wind and less sunshine.

The Telegraph quoted the study’s author as saying, “Therefore we advise to dress appropriately when going outside on cold days or maybe move to [a] warmer climate.”

The Sun offered some more realistic advice: “So what can you do to reduce your risk if you don't have the time or money to jet off to Barbados for the winter? It goes without saying that you should get a flu jab if you're at all vulnerable. Over 65s, children under ten and certain people with asthma can get one for free on the NHS.”

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