Cardiovascular Support. Dietary Supplement. Vegan. Quercetin is a flavonol (a subclass of flavonoids) and is an effective antioxidant. Bioflavonoid Supports Immune and Cardiovascular Health. Immune Support. Dietary Supplement. Vegan. Gluten Free. Non GMO Project Verified. Quercetin is a bioflavonoid antioxidant found in onions, green leafy vegetables, and fruits such as apples and cherries. Quercetin supports healthy cellular function, cardiovascular health, and has been shown to support a healthy immune response.