Vitamin C: the pathway in the body

This page shows the biochemical pathway behind the laboratory value Vitamin C (ascorbic acid): which stations follow one another, which enzymes carry out each step and which cofactors they use. Every statement has a source. The page describes general textbook knowledge and says nothing about any individual person.

In brief

Vitamin C (ascorbic acid) is a water-soluble vitamin that humans cannot make themselves. It donates electrons and thereby keeps iron and copper in enzymes in working order, for example in the prolyl 4-hydroxylase of collagen formation.

The pathway step by step

1. Vitamin C in food → Into the gut cell SVCT1 · Sodium The transporter SVCT1 moves ascorbate together with sodium into the cells of the small intestinal wall. The oxidised form, dehydroascorbate, enters via sugar transporters. Source 2
2. Into the gut cell → Ascorbate in the blood From the gut cell, ascorbate passes into the blood and through it reaches all tissues. Source 2
3. Ascorbate in the blood → Kidney SVCT1 · Sodium The kidney filters ascorbate from the blood and retrieves it via the same transporter, SVCT1. What is not retrieved leaves the body in the urine. Source 2
4. Ascorbate in the cell → Ascorbate as cofactor Many enzymes carry iron or copper in their active centre. Ascorbate donates an electron and keeps the metal in the form in which the enzyme can work. Source 3, 4, 5
5. Ascorbate in the cell → Ascorbyl radical When ascorbate donates an electron, the ascorbyl radical forms briefly. Two of these particles react with each other: one becomes ascorbate again, the other dehydroascorbate. Source 1
6. Ascorbyl radical → Dehydroascorbate Dehydroascorbate carries no more electrons. Enzymes that use glutathione or thioredoxin can turn it back into ascorbate. Source 1
7. Dehydroascorbate → Diketogulonic acid If dehydroascorbate is not converted back, it breaks down in water to 2,3-diketogulonic acid and further to smaller acids such as oxalate, which the body excretes. Source 1
8. Proline in collagen → Hydroxyproline Prolyl 4-hydroxylase · Iron, α-Ketoglutarate Prolyl 4-hydroxylase attaches an OH group to proline. The enzyme contains iron and uses up α-ketoglutarate; ascorbate keeps the iron in its reactive form. Source 3
9. Hydroxyproline → Collagen triple helix Only with the OH groups do three collagen chains wind stably around each other. This form gives collagen its tensile strength; it is found in skin, vessel walls, bone and tendons. Source 3

Cofactors in this pathway

• Sodium — Drives the transporters SVCT1 and SVCT2, which carry ascorbate into cells Source 2In the ORY catalogue as a laboratory value: Natrium (intrazellulär)
• Iron — Metal centre of prolyl 4-hydroxylase, which ascorbate keeps reactive Source 3In the ORY catalogue as a laboratory value: Eisen
• Copper — Metal centre of monooxygenases to which ascorbate supplies electrons Source 4In the ORY catalogue as a laboratory value: Kupfer (Cu)
• α-Ketoglutarate — Consumed by prolyl 4-hydroxylase in each hydroxylation Source 3In the ORY catalogue as a laboratory value: Alpha-Ketoglutarat (2-Oxoglutarat)
• Glutathione — Reduces dehydroascorbate back to ascorbate Source 1, 6In the ORY catalogue as a laboratory value: Glutathion (GSH)
• Selenium — Component of thioredoxin reductase, which reduces dehydroascorbate to ascorbate Source 6In the ORY catalogue as a laboratory value: Selen
• Niacin (NADPH) — NADPH supplies thioredoxin reductase with the electrons for recycling Source 6

Sources

1. Linster CL, Van Schaftingen E. Vitamin C. Biosynthesis, recycling and degradation in mammals. FEBS J 2007 · PubMed 17222174
2. Padayatty SJ, Levine M. Vitamin C: the known and the unknown and Goldilocks. Oral Dis 2016 · PubMed 26808119
3. Salo AM, Myllyharju J. Prolyl and lysyl hydroxylases in collagen synthesis. Exp Dermatol 2021 · PubMed 32969070
4. Prigge ST, Mains RE, Eipper BA et al. New insights into copper monooxygenases and peptide amidation: structure, mechanism and function. Cell Mol Life Sci 2000 · PubMed 11028916
5. Rebouche CJ. Ascorbic acid and carnitine biosynthesis. Am J Clin Nutr 1991 · PubMed 1962562
6. May JM, Mendiratta S, Hill KE, Burk RF. Reduction of dehydroascorbate to ascorbate by the selenoenzyme thioredoxin reductase. J Biol Chem 1997 · PubMed 9278416

Related pathways

• 8-OHdG — Eisen, Kupfer (Cu)
• Iodine — Natrium (intrazellulär), Eisen
• Nitrosative stress — Eisen, Glutathion (GSH)
• Thyroid hormones — Natrium (intrazellulär), Eisen
• Borrelia — Eisen, Selen

As of 2026-09-16. Draft written by Claude to schema v2; sources checked in PubMed; expert review pending
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