However, at doses above 1 g/day, absorption falls to less than 50% and absorbed, unmetabolized ascorbic acid is excreted in the urine. Approximately 70%–90% of vitamin C is absorbed at moderate intakes of 30–180 mg/day. Oral vitamin C produces tissue and plasma concentrations that the body tightly controls. The physiologic importance of dehydroascorbic acid uptake and its contribution to overall vitamin C economy is unknown. In vitro studies have found that oxidized vitamin C, or dehydroascorbic acid, enters cells via some facilitated glucose transporters and is then reduced internally to ascorbic acid. Cells accumulate vitamin C via a second specific transport protein. The intestinal absorption of vitamin C is regulated by at least one specific dose-dependent, active transporter. Insufficient vitamin C intake causes scurvy, which is characterized by fatigue or lassitude, widespread connective tissue weakness, and capillary fragility. In addition to its biosynthetic and antioxidant functions, vitamin C plays an important role in immune function and improves the absorption of nonheme iron, the form of iron present in plant-based foods. Ongoing research is examining whether vitamin C, by limiting the damaging effects of free radicals through its antioxidant activity, might help prevent or delay the development of certain cancers, cardiovascular disease, and other diseases in which oxidative stress plays a causal role. Vitamin C is also an important physiological antioxidant and has been shown to regenerate other antioxidants within the body, including alpha-tocopherol (vitamin E). Collagen is an essential component of connective tissue, which plays a vital role in wound healing. Vitamin C is required for the biosynthesis of collagen, L-carnitine, and certain neurotransmitters vitamin C is also involved in protein metabolism. Humans, unlike most animals, are unable to synthesize vitamin C endogenously, so it is an essential dietary component. Vitamin C, also known as L-ascorbic acid, is a water-soluble vitamin that is naturally present in some foods, added to others, and available as a dietary supplement. For a general overview of Vitamin C, see our consumer fact sheet on Vitamin C.įor information on vitamin C and COVID-19, see Dietary Supplements in the Time of COVID-19. This is a fact sheet intended for health professionals.

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