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Loreben Tuquero
By Loreben Tuquero March 26, 2024

Findings on short-term heat exposure had no relationship to COVID-19 vaccines

If Your Time is short

  • A study out of Kentucky’s University of Louisville found that short-term heat exposure can increase inflammation and impair a person’s immune system.

  • The study involved participants who were recruited in 2018 and 2019, before the COVID-19 pandemic. It had nothing to do with COVID-19 vaccines.

  • Learn more about PolitiFact’s fact-checking process and rating system.

Spring is here, and people are spending more time in the sun.

Just in time, an article warned that such sun exposure could increase heart disease risk. But one social media post said the study underpinning the article isn’t what it seems.

"The reason they’re trying to sit here and say everything causes heart attacks is because they’re trying to cover up the side effects of the vax," said a man in a March 20 Instagram post, his image superimposed over a March 19 Daily Mail article headlined, "Sunbathing for just ONE DAY may increase your risk of heart disease - and stop the body fighting infections, study finds."

This post was flagged as part of Meta’s efforts to combat false news and misinformation on its News Feed. (Read more about our partnership with Meta, which owns Facebook and Instagram.)

The Daily Mail article referred to a study from the University of Louisville in Kentucky. Preliminary research, presented at an American Heart Association conference March 18-21, found that short-term high heat exposure could increase inflammation and impair normal immune system functions, which could accelerate cardiovascular disease.

The study involved 624 participants recruited in 2018 and 2019, before the COVID-19 pandemic began.

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In a news release, the American Heart Association said, participants had blood tests in Louisville study sites during the summer. The researchers analyzed the blood samples for links between heat levels and immune system activation. 

Daniel Riggs, University of Louisville assistant medicine professor and the study’s lead author, told PolitiFact the Daily Mail headline didn’t accurately represent the study’s findings. He said the study aimed mainly to determine whether short-term heat was linked to inflammation markers, not increased risk of heart disease. 

"Some of these markers are related to heart disease, but we didn’t study if there was an increased risk of heart disease related to high temperatures," he said. "And I would say our findings definitely do not imply that sunbathing could stop the body fighting infections. That is something we also did not study."

The heat levels that the researchers factored in included air temperature, humidity and wind speed. The American Heart Association news release said that the researchers "did not know how long individuals were exposed to outdoor heat stress before their blood was drawn." 

"It doesn’t have anything to do with vaccines or COVID," Riggs said.

We rate the claim that this study was a cover-up for COVID-19 vaccine side effects False. ​

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

Our Sources

Instagram post (archived), March 20, 2024, Sunbathing for just ONE DAY may increase your risk of heart disease - and stop the body fighting infections, study suggests, March 19, 2024

Email exchange with Daniel Riggs, University of Louisville assistant professor of medicine, March 25, 2024

American Heart Association, Heat exposure may increase inflammation and impair the immune system, March 19, 2024

American Heart Association, P297 - Associations Between Short-Term Outdoor Heat Measures and Markers of Immune Response and Inflammation, accessed March 22, 2024

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Findings on short-term heat exposure had no relationship to COVID-19 vaccines

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