Quercetin can be found in small amounts in many fruits, vegetables, and herbs, such as apples, onions, and cilantro. One of the richest food sources of quercetin is capers, the pickled flower buds of the caperberry plant. Natural Factors Quercetin supplements are made from the flower bud of Sophora japonica, the Japanese pagoda tree.

First identified by Albert Szent-Györgyi, the Nobel Prize-winning discoverer of vitamin C, quercetin is often referred to somewhat mysteriously as a “vitamin-like” molecule. Quercetin is actually a bioflavonoid, a distinguished member of a large family of phytonutrients with biological activity in the human body.*