Quercetin is a type of flavonoid that functions as an antioxidant, an anti-inflammatory and an antihistamine. Consuming sufficient amounts of quercetin may help lower your risk for heart disease, high blood pressure, high cholesterol, cancer, allergies and asthma, according to the University of Maryland Medical Center.
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Apples, citrus fruits, onions, parsley, red wine and tea are some of the best food sources for quercetin. Other foods, including beans, bilberries, blackberries, blueberries, dark cherries, grapes, buckwheat, leafy green vegetables and olive oil, also contain some quercetin. However, to experience the possible beneficial health effects of quercetin, you need to consume more than you get from food alone, according to Tufts New England Medical Center.
You can purchase quercetin supplements in water-soluble form or as a capsule or pill. Makers of quercetin chalcone claim that this form is more easily absorbed by your body, but more evidence is needed to support this claim. Supplements that contain both quercetin and bromelain might also be easier for your body to absorb.
The recommended dosage for quercetin depends on why you are taking this supplement. However, most people take between 300 and 1,000 mg per day, split into two or three doses, according to the University of Maryland Medical Center. Do not take more than this without the supervision of your doctor.
The most common side effects of quercetin are upset stomach, nausea and headache. High doses of quercetin may cause kidney damage, so avoid this supplement if you have kidney disease. Children and pregnant and breastfeeding women should also avoid this supplement since its safety hasn't been verified for these populations. Quercetin may interact with various medications including chemotherapy medications, anticoagulants, cyclosporine and corticosteroids.