Supplemental sports food for extemporaneous useIs it time to give your immune and respiratory system some extra attention? The flavonoid Quercetin maybe your answer. Quercetin is a naturally occurring antioxidant commonly found in fruit and vegetables, including dark berries, grapes and dark leafy greens. Green tea and red wine are also known to have notable amounts of Quercetin. But if you can't get enough of this flavonoid naturally in your diet then you could be looking to take this as a daily supplement.