Vitamin C, also known as ascorbic acid or ascorbate, plays two important roles in the body. First, it is a cofactor or cosubstrate for eight enzyme systems involved in various functions, including collagen synthesis, ATP synthesis in mitochondria, and hormone biosynthesis. Second, vitamin C is a powerful water-soluble antioxidant with a vital role in protecting cells and tissues from damaging oxidizing agents, including superoxides, hydroxyl radicals, and other free radicals. All these functions derive from one fundamental property: vitamin C is a powerful reducing agent (or electron donor) capable of neutralizing reactive oxidants.
Related functions performed by vitamin C include regenerating vitamin E to its active state, promoting iron absorption in the intestines by keeping iron in its reduced form, and participation in DNA transcription and protein synthesis regulation.
The richest dietary sources of vitamin C include cantaloupe, grapefruit, honeydew, kiwi, mango, oranges and other citrus fruits, strawberries, and watermelon. The richest vegetable sources include asparagus, broccoli, brussels sprouts, dark green leafy vegetables, and peppers.
Although vitamin C is generally non-toxic, very high dosages (several grams or more) may cause or contribute to gastrointestinal distress and diarrhea.