Natural Factors C Extra + Quercetin contains 500 mg of vitamin C and 250 mg of quercetin. Vitamin C is a powerful antioxidant which supports healthy bones, cartilage, teeth, and gums.* It helps protect cells against free radical damage and vitamin C deficiencies in the daily diet, and supports healthy cell growth.* Quercetin is one of the most well-known antioxidant bioflavonoids. A free radical scavenger, quercetin helps support healthy sinus, respiratory, and immune system function.* They are easy-to-swallow capsules as compared to similar size tablets.