title: Vitamin C: the known and the unknown and Goldilocks.
abstract: Vitamin C (Ascorbic Acid), the antiscorbutic vitamin, cannot be synthesized by humans and other primates, and has to be obtained from diet. Ascorbic acid is an electron donor and acts as a cofactor for fifteen mammalian enzymes. Two sodium-dependent transporters are specific for ascorbic acid, and its oxidation product dehydroascorbic acid is transported by glucose transporters. Ascorbic acid is differentially accumulated by most tissues and body fluids. Plasma and tissue vitamin C concentrations are dependent on amount consumed, bioavailability, renal excretion, and utilization. To be biologically meaningful or to be clinically relevant, in vitro and in vivo studies of vitamin C actions have to take into account physiologic concentrations of the vitamin. In this paper, we review vitamin C physiology; the many phenomena involving vitamin C where new knowledge has accrued or where understanding remains limited; raise questions about the vitamin that remain to be answered; and explore lines of investigations that are likely to be fruitful.
authors.affiliation: Molecular and Clinical Nutrition Section, Digestive Diseases Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland, USA.
authors.forename: S J
authors.initials: SJ
authors.lastname: Padayatty
authors.affiliation: Molecular and Clinical Nutrition Section, Digestive Diseases Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland, USA.
authors.forename: M
authors.initials: M
authors.lastname: Levine
mesh_terms: D001205:Ascorbic Acid / Q000378:metabolism / Q000502:physiology*; D006801:Humans; D066298:In Vitro Techniques; D009909:Oral Health; D064167:Recommended Dietary Allowances
chemical_list: D001205:Ascorbic Acid
keywords: dehydroascorbic acid; dose-concentration relationship; recommended dietary allowance; scurvy; vitamin C; vitamin C transport