Vitamin C and Bio-Quercetin Phytosome is a high-potency vitamin C supplement enhanced with an ultra-absorbable form of quercetin. Vitamin C is a powerful antioxidant that also supports immune health, a healthy cardiovascular system, whole body health, and more. Quercetin is a flavonoid that complements vitamin C’s health benefits. And our NEW bio-quercetin is encased in a plant-derived phytosome delivery system, which makes it up to 50 times more bioavailable than a dose of standard quercetin.