Quercetin was discovered by J. Rigaud in 1854. It is a natural, water-soluble pigment found in plant foods. It is the most abundant and common flavonoid in the human diet, noted for its high antioxidant activity. Many plants, whether considered medicinal or not, owe much of their benefits to their high levels of quercetin. For example, some types of onion, such as red onion, contain so much quercetin that the compound represents 10% of their dry weight. Experimental studies have shown it has numerous effects on the body, including inhibiting both the production and release of histamine. It is especially known for its antioxidant action. Recent studies demonstrate its contribution to cardiovascular well-being. Quercetin is found in many fruits. In the United Kingdom, apples (in addition to onions) also provide the highest amounts of quercetin through diet. Each 500 mg tablet provides significantly more quercetin than 1 kg of apples.
