Vitamin C, also known as ascorbic acid and ascorbate, is a vitamin found in various foods and sold as a dietary supplement. It is used to prevent and treat scurvy. Vitamin C is an essential nutrient involved in the repair of tissue and the enzymatic production of certain neurotransmitters? Vitamin C, or ascorbic acid, is a water-soluble vitamin well known for its role in supporting a healthy immune system. ... As an antioxidant, vitamin C fights free radicals in the body which may help prevent or delay certain cancers and heart disease, and promote healthy aging. Foods rich in vitamin C include broccoli, cantaloupe, cauliflower, kale, kiwi, orange juice, papaya, red, green or yellow pepper, sweet potato, strawberries, and tomatoes. For adults, the recommended daily amount for vitamin C is 65 to 90 milligrams (mg) a day, and the upper limit is 2,000 mg a day. Although too much dietary vitamin C is unlikely to be harmful, megadose of vitamin C supplements might cause: Diarrhea