Heart attacks more likely when it’s cold out, study finds

BARCELONA, Spain — If heart attacks run in your family, it may be better to live in warmer climates. That’s because a new, long-term study finds colder weather seems to play a role in suffering a heart attack, with a significant uptick in patients on cold days.

Researchers in Sweden examined a study of 280.873 heart attack patients from the country between January 1998 and December 2013. The team checked the weather conditions for the area where each attack was suffered and recorded data including temperature, wind levels, humidity, amount of precipitation, and sunshine duration for that day. Weather data was obtained using hundreds of stations from the Swedish Meteorological and Hydrological Institute.

Snow covering a city street
A new study finds that cold weather may trigger heart attacks, with the odds of suffering one much higher in sub-freezing temperatures.

After evaluating the average number of heart attacks per day and the average daily minimum temperature, researchers noticed that more heart attacks took place on cold days compared to warmer ones — a trend that was consistent nationwide.

Specifically, the likelihood of a heart attack was higher when temperatures were below 0°C (32°F). About four more heart attacks per day are suffered under those conditions compared to days when the average minimum temperature was above 10°C (50°F).

“There is seasonal variation in the occurrence of heart attack, with incidence declining in summer and peaking in winter,” says first author. Dr Moman A. Mohammad, from the Department of Cardiology at Lund University and Skane University Hospital, in a press release. “It is unclear whether this is due to colder temperatures or behavioural changes.”

Mohammad and his team also noted that attacks were more likely on days that were windier, more humid, or when there was less sunshine.

The team controlled for conditions including age, previous heart attacks suffered, medications, and various ailments.

“The findings were the same across a large range of patient subgroups, and at national as well as regional levels, suggesting that air temperature is a trigger for heart attack,” adds Mohammad.

Because the study was strictly observational, scientists couldn’t confirm that it’s cold weather specifically that triggers heart attacks — perhaps mental health or stress worsens for people in the winter, while stress levels decline in more pleasant climates. (Of course, one recent study pointed to high levels of heat causing people to be moodier and unfriendly.)

Mohammad noted that cold weather leads us to shiver and make our heart rates rise, which then raises body temperature. Similarly, chilly air causes blood vessels to constrict and arterial blood pressure to rise, which could pose problematic for people with significant plaque blocking their coronary arteries.

He says common wintertime colds or coming down with the flu may also play a role in the results, as well as people staying indoors more frequently.

“Seasonal-dependent behaviours such as reduced physical activity and dietary changes could play a role in the increased occurrence of heart attack during colder weather,” he says.

The findings were presented Monday at the European Society of Cardiology annual Congress, which continues meeting through Wednesday.


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