Bioflavonoid substances are widely distributed in nature. Onion has a rich content of Quercetin. Flavonoids are phenolic compounds naturally occurring that are abundantly present in plants and seaweed. We take it from fruits, vegetables, tea and red wine (as a few examples) Most important types are: anthocyanins, chalcons, flavonols, flavones, flavonoids and tannins. No risk for toxic nor side-effects in humans have been found. They appear naturally in the breast milk in amounts related to mother's diet. Attributed anti-oxidant activity and other properties that have not been fully shown yet, as amelioration of capillary vessel function which is a reason to be used for treatment of venous insufficiency (varicose veins), hemorrhoids and prevention of arteriosclerosis.