Vitamin C with Quercetin - Powerful Immune Support* This synergistic formula combines the antioxidant support of Vitamin C with citrus bioflavonoids and quercetin.* • A powerful antioxidant, Vitamin C supports healthy immune system responses.*• Flavonoids are beneficial for respiratory health and the body's cytokine responses.*Each of these ingredients are powerful on their own, but when combined provide superior support for the immune system.*