The flu is caused by influenza viruses that infect the nose, throat, and lungs, the Centers for Disease Control and Prevention (CDC) explains. And while many people develop mild flu symptoms—runny news, chills, body aches, and fever—the illness can lead to severe illness and even death. What's more: the flu can cause heart complications, especially in people who have underlying cardiac issues.
"Even though the flu is respiratory, it can still impact the rest of your body—including your heart," Nicole Weinberg, MD, cardiologist at Providence Saint John's Health Center in Santa Monica, California. A 2018 study published by the New England Journal of Medicine found that deaths from heart conditions and the flu tend to spike around the same time. Despite that, a new Journal of the American Heart Association study found that the vaccination rate for adults under 65 years old, who have heart disease, is less than 50 percent. (By comparison, 80 percent of older adults with heart disease get the flu shot.)
What's the connection between the flu and heart complications? A lot of it comes down to bodily inflammation caused by the influenza virus, explains infectious disease expert Amesh A. Adalja, MD, a senior scholar at the Johns Hopkins Center for Health Security. Of course, not all heart issues are the same.
4 ways getting the flu can impact heart health
1. Increased blood pressure
The flu can even cause your blood pressure to go up, raising your risk of stroke and other health complications. "Whenever the body is under stress for a number of different reasons, you can have these responses in your system," Dr. Weinberg says. "Your body is just processing through all the insults with the virus." Dr. Weinberg says that doctors follow blood pressure readings in people who already have blood pressure issues "very closely" when they have the flu for this reason.
2. Blood clots
There are a few reasons why people have an increased risk of developing blood clots when they have the flu, Dr. Weinberg says. "There are a lot of things happening in the body when you're infected with any sort of acute illness," she points out, including increased protein levels, like prothrombin, which is released into your bloodstream and can lead to more clots. Another potential issue, Dr. Weinberg says, is that laying in bed can increase your risk of clots. "You have less blow flow when you're bedbound, and that can cause more clots to form," she says.
3. Myocarditis or pericarditis
Myocarditis is an inflammation of the heart muscle, while pericarditis is inflammation of the outer lining of the heart, according to the CDC. Both conditions can cause chest pain, shortness of breath, and feeling like you have a fast, fluttering, or pounding heart—and, in rare cases, you can experience this while you're sick with the flu or afterward, says Jennifer Wong, MD, a cardiologist and medical director of Non-Invasive Cardiology at MemorialCare Heart and Vascular Institute at Orange Coast Medical Center in Fountain Valley, California.
"It's likely an immune-mediated response," she says. Meaning, these conditions can happen as a result of your immune system kicking into gear to fight the flu. "Myocarditis and pericarditis may also be caused by direct viral invasion of cardiac tissue," Dr. Adalja says. That is, the flu virus can actually get into your heart, where it can cause damage.
4. Heart attack
Research has found a link between the flu and heart attack. The aforementioned study published in the New England Journal of Medicine found that the risk of having a heart attack is six times higher the week after a person is diagnosed with having the flu than it is during any other time of the year. A 2020 study published in Annals of Internal Medicine analyzed data from more than 80,000 American adults hospitalized with the flu over eight seasons and found that serious heart complications, like a heart attack, happened in one out of every eight patients.
Inflammation from the flu can cause plaques, cholesterol, fatty substances, waste products, and calcium, in the wall of your arteries to rupture, leading to blockages and heart attacks, Dr. Wong says.
How to protect yourself from the flu
Experts agree that the best thing you can do is to get vaccinated against the flu. "The vaccine is the best way to prevent or minimize cardiovascular complications," Dr. Adalja says. Dr. Weinberg agrees. While the flu vaccine isn't perfect, she points out that getting it will dramatically lower your risk of getting seriously ill or developing cardiac complications if you happen to get the virus. In fact, a 2021 study published in Vaccine suggests that flu vaccinations resulted in a 26 percent lower risk of ICU admission rate and 31 percent lower risk of death compared to unvaccinated people. And if you're not exactly sure where to get jabbed, the CDC has a vaccine locater tool that you can use to get your flu shot (and your COVID-19 vaccine, too).
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