Ascorbic acid, also known as vitamin C, is a water-soluble vitamin that is essential for human health. Unlike most animals, humans cannot synthesize vitamin C endogenously, so it must be obtained through the diet. Vitamin C is required for the biosynthesis of collagen, L-carnitine, and certain neurotransmitters, and is also involved in protein metabolism. Good sources of vitamin C include citrus fruits, broccoli, and tomatoes. Vitamin C is sensitive to light, air, and heat, so it is best to eat fruits and vegetables raw or lightly cooked to get the most vitamin C. Vitamin C is available in a variety of forms, including tablets, capsules, and chewables, as well as powdered crystalline, effervescent, and liquid forms. Vitamin C is also available in extended-release capsules and tablets, lozenges, chewable gels, and liquid drops. Vitamin C is used as a dietary supplement when the amount of ascorbic acid in the diet is not enough, and is also used to prevent and treat scurvy. Vitamin C improves the absorption of non-heme iron, the type of iron found in plant foods such as leafy greens.