Influenza (flu) is a respiratory illness caused by viruses. It infects the nose, throat, and sometimes the lungs, causing symptoms like fever, body aches, and coughing. A stroke is a medical emergency occurring when blood flow to the brain is interrupted, either by a blocked (ischemic) or burst (hemorrhagic) blood vessel. This deprives brain cells of oxygen.
Understanding the Connection
Research indicates an association between flu infection and increased stroke risk. Respiratory infections, especially the flu, can trigger cardiovascular events like stroke. While flu doesn’t directly cause a stroke, it creates conditions that heighten its likelihood. The risk of ischemic stroke can increase significantly in the days and weeks following a flu-like illness. One study found the risk of heart attack and ischemic stroke more than doubled in patients aged 50 and older within two weeks of a mild flu infection. This elevated risk can persist for up to two months.
Biological Pathways to Stroke
The flu virus can influence stroke risk through several biological mechanisms. One pathway involves the body’s inflammatory response. When the flu virus enters, it triggers a widespread inflammatory reaction. This systemic inflammation can affect blood vessels, promoting instability in arterial plaques. If these plaques rupture, they can lead to blood clots that may travel to the brain and cause a stroke.
Flu infection can also increase the blood’s tendency to clot (hypercoagulability). The infection can increase blood viscosity, making it thicker and more prone to forming dangerous clots. These clots can obstruct blood flow to the brain, resulting in an ischemic stroke. Platelets, involved in clotting, can also contribute to clot formation.
Damage to the inner lining of blood vessels (endothelial dysfunction) also plays a role. The flu virus or its intense immune response can harm endothelial cells. When this lining is damaged, blood vessels become more susceptible to blockages and narrowing, impairing blood flow. This can make it easier for clots to adhere or for existing plaques to rupture, increasing stroke risk.
Flu can also lead to cardiac complications that indirectly raise stroke risk. It can exacerbate pre-existing heart conditions or cause new ones, like myocarditis or atrial fibrillation. These cardiac issues can increase blood clot formation within the heart, which may then travel to the brain and cause a stroke. Atrial fibrillation is a known risk factor for ischemic stroke.
Who Is Most at Risk?
Certain individuals face a higher likelihood of stroke following a flu infection due to underlying health status or demographic factors. Elderly individuals, especially those aged 65 and older, are at elevated risk. Their immune systems may be less robust, and they often have co-existing health conditions that increase vulnerability to severe flu complications and stroke.
People with pre-existing cardiovascular diseases are also susceptible. This includes individuals with high blood pressure, high cholesterol, atherosclerosis, or a prior history of stroke or TIA. The flu can stress an already compromised cardiovascular system, making it more prone to adverse events like stroke. Approximately half of adults hospitalized with the flu have heart disease.
Individuals with diabetes also face an increased risk of flu-associated stroke. Diabetes can affect blood vessel health and immune function, making them more vulnerable to the inflammatory and clotting effects of flu. People with compromised immune systems, due to medical conditions or medications, may experience more severe flu infections, further heightening their stroke risk. Smokers and individuals with obesity are also at increased risk, as these factors contribute to cardiovascular disease and can worsen the body’s response to infection.
Steps to Reduce Your Risk
Taking proactive steps can reduce the risk of flu-associated stroke. The most effective measure is getting an annual flu vaccination. The flu shot helps prevent severe illness, which reduces systemic inflammation and other physiological changes that can trigger a stroke. Studies indicate flu vaccination can decrease stroke incidence, especially in individuals with underlying health conditions like atrial fibrillation, diabetes, or hypertension.
Managing underlying health conditions is also important. Individuals with high blood pressure, diabetes, high cholesterol, or existing heart disease should work with healthcare providers to keep these conditions well-controlled. Adhering to prescribed medications and regular monitoring can help stabilize cardiovascular health and minimize the impact of a flu infection.
Adopting a healthy lifestyle provides broad protection. This includes maintaining a balanced diet, engaging in regular physical activity, and avoiding smoking. These habits contribute to overall cardiovascular health, making the body more resilient to viral infections.
Seeking prompt medical attention for severe flu symptoms or any signs of stroke is crucial. Recognizing stroke symptoms early, often remembered by the FAST acronym (Face drooping, Arm weakness, Speech difficulty, Time to call emergency services), allows for timely intervention, which can minimize brain damage and improve outcomes. For individuals with heart disease or a history of stroke, healthcare providers may recommend antiviral treatment if flu is suspected or confirmed.