The Flu Can Increase Your Heart Attack Risk, Study Finds

NEW YORK, NY — As a particularly severe flu season continues apace, new research suggests that catching the virus can do more than ruin your week — it can cause a six-fold increase in your risk of a heart attack.

According to a new study written by Canadian researchers and published in the New England Journal Medical Journal, people who were diagnosed with the flu had a significantly increased chance of having a heart attack — also called a myocardial infarction — within the first week of the disease.

“Our findings are important because an association between influenza and acute myocardial infarction reinforces the importance of vaccination,” said Dr. Jeff Kwong, lead author of the study and a scientist at Institute for Clinical Evaluative Sciences and Public Health Ontario. The findings, "combined with previous evidence that influenza vaccination reduces cardiovascular events and mortality, support international guidelines that advocate for influenza immunization in those at high risk of a heart attack."

To conduct the study, the researchers analyzed nearly 20,000 cases of adults with the flu in Ontario. Of these, 332 were hospitalized for a heart attack within a year of their diagnosis with the flu. And 20 of these cases occurred within a week of the diagnosis.

This means these people were six times more likely to have a heart attack than similar people who didn't get the flu, the researchers said. This increase could be even higher for people at high risk of a heart attack.

Dr. Andy Miller, the chair-elect for the Board of Governors at the American College of Cardiology, was impressed with the study and found the findings to be important.

A heart attack has typically been thought of as being primarily caused by a build-up of plaque in the blood vessels over time. However, Miller explained, this study points to another potential route-cause of heart attack: inflammation that can cause the plaque in blood vessels to rupture.

This study suggests that the inflammation caused by respiratory infections — and the flu in particular — may be a significant cause of heart attacks. This points to some potential treatments that could reduce the risk, Miller said.

"There might be a line of therapies preventing inflammation that might be useful," he explained.

Miller said the study makes a persuasive case, even if it may seem limited.

"It is small number of people who actually had heart attacks during the study," he said. But the study used a control group, strengthening its findings, and showed the acute effects of the flu on heart attacks in a clear timeline. "I think the methods they used are the correct ones."

And as the study itself notes, since at least 2004, research has suggested that a flu vaccine provided some protection against heart attack risk. This new research is a powerful confirmation of this effect.

The researchers said that, in addition to getting a flu shot, they advise anyone who does get infected to be particularly attentive to symptoms of a heart attack during the first week.

“People at risk of heart disease should take precautions to prevent respiratory infections, and especially influenza, through measures including vaccinations and handwashing,” said Kwong.

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