Heart health warnings about cold weather are real, and predate the pandemic

For years, scientists have cautioned people about the health effects of winter weather, including blood clots and heart problems. To skeptics of vaccines, those conditions sound familiar.

And some recent posts are recasting these warnings as a cover-up for rare blood clots and heart complications associated with the COVID-19 vaccines. 

"Just in case anyone was confused, winter does not cause blood clots and heart attacks," said one since-deleted Facebook post. 

Another person, sharing a headline that said "researchers warn that cold weather can cause blood clots and heart attacks," commented: "We are getting a lot of education on random things that can cause heart attacks."

"Just in case you are confused," a third sharing a similar headline said. "Winter does NOT cause blood clots and heart attacks. But I know something that does (use your imagination)." 

There have been rare cases of blood clots and heart complications associated with the COVID-19 vaccines.

But they’re also a risk in cold weather, and warnings about them aren’t new. Researchers have discussed this for years, before COVID-19.

These posts were flagged as part of Facebook’s efforts to combat false news and misinformation on its News Feed. (Read more about our partnership with Facebook.)

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"As temperatures start to fall, your risk of a heart attack begins to climb," says a 2016 blog post on the Harvard Medical School website. The post quotes Randall Zusman, a cardiologist at Massachusetts General Hospital, who said that cold weather can decrease the supply of oxygen-rich blood to the heart and potentially force the heart to work harder, setting the stage for a heart attack. Because of this, the American Heart Association says that some people should avoid sudden exertion in cold weather, such as lifting a heavy shovel of snow. 

A 2018 study in the JAMA Cardiology journal found that heart attacks increase most when the temperature drops below freezing.

Cleveland HeartLab says on its website, "The cold air alone can raise blood pressure, slow down the flow of blood to the heart, and help blood clots form. 

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Comilla Sasson, vice president for science and innovation for emergency cardiovascular care at the American Heart Association, told AFP that there are "several studies with strong correlations to cold weather heart health concerns," including the increased formation of blood clots. 

Sasson said studies have also shown an increase in heart attacks shortly after people get the flu — and winter is flu season. On Dec. 7, the American Heart Association posted a warning on its website: "Heart attack deaths more likely during winter holiday season than any other time of year." 

We rate claims that these warnings are fake and covering up rare vaccine side effects False.