What is Vitacost Advan-C with Quercetin and Citrus Bioflavonoids?Vitacost Advan-C with Quercetin and Citrus Bioflavonoids is a synergistically formulated combination of a gentler form of vitamin C plus citrus bioflavonoids and quercetin. Advan-C is an acid-neutralized form of vitamin C, meaning its non-irritating to your digestive system. Bioflavonoids are plant compounds known for their antioxidant benefits. Theyre abundant in the pulp and rinds of citrus fruits as well as in other fruits, vegetables and teas. Quercetin is a type of bioflavonoid also found in plant foods (especially apples, onions and green and black teas), with antioxidant properties.