Vitamin C (ascorbic acid) !

Vitamin C is needed to make stable collagen, absorb iron and protect against oxidative damage; its lack causes scurvy.

Updated 2026-11-01

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Key facts

Cofactor of prolyl and lysyl hydroxylases, which hydroxylate collagen; without it collagen cannot form a stable triple helix.
It keeps the iron of those enzymes in the ferrous state (Fe²⁺) and reduces dietary iron so the duodenum can absorb it.
Also used by dopamine β-hydroxylase (dopamine → noradrenaline, with copper) and carnitine synthesis.
Deficiency: scurvy, with bleeding gums, perifollicular petechiae, corkscrew hairs and poor wound healing.

Sources: fresh fruit and vegetables (guava, citrus, kiwi, peppers, broccoli, potatoes). Humans cannot make it because we lost the enzyme gulonolactone oxidase. Heat and storage destroy it.
Chemistry: ascorbate gives up two electrons and becomes dehydroascorbate; glutathione regenerates it.
Collagen: hydroxyproline forms hydrogen bonds that stabilise the triple helix; hydroxylysine allows cross-links. Without them vessels, skin, gums and bone become fragile.
Antioxidant: it regenerates vitamin E and neutralises radicals in the water of the cytoplasm and plasma.
Causes of deficiency: a diet without fruit or vegetables (older adults living alone, alcoholism, eating disorders, very restrictive diets in children), smoking (raises turnover), dialysis.
Excess (supplements): diarrhoea, oxalate kidney stones (ascorbate breaks down to oxalate) and iron overload in people with haemochromatosis.
Lab: plasma or leucocyte ascorbate (leucocyte levels reflect stores better); scurvy is usually diagnosed clinically and by the response to treatment.

A six-carbon lactone with an enediol group (two hydroxyls on a double bond) that gives up electrons easily.
The L form is active; dehydroascorbate is its oxidised form.

Taking vitamin C with meals increases absorption of non-heme iron from plant foods.
Scurvy is still seen in children with autism or very selective diets and in adults with alcoholism or malnutrition.
Methaemoglobinaemia can be treated with ascorbic acid when methylene blue is unavailable or contraindicated.

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Why does lack of vitamin C make vessels and gums fragile?

Without it prolyl and lysyl hydroxylases fail; unhydroxylated collagen cannot form a stable triple helix.

How does vitamin C help absorb iron?

It reduces dietary ferric iron (Fe³⁺) to ferrous iron (Fe²⁺), the form carried by DMT1 in the duodenum.

Which skin signs are typical of scurvy?

Petechiae around hair follicles, corkscrew hairs, easy bruising and wounds that do not heal.

What risks come with high-dose vitamin C supplements?

Oxalate kidney stones, diarrhoea and, in haemochromatosis, greater iron absorption.

Molecules are shown in their neutral form, as the databases deposit them; in the cell the acids and phosphates are ionised.

Educational information, not medical advice. For any symptom, see a health professional.

Sources: L-Ascorbic Acid (CID 54670067) (PubChem, NCBI, 2026) · Public domain; Vitamin C: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2026); Scurvy: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2026); Vitamin C: MedlinePlus (MedlinePlus, US National Library of Medicine, 2026); Textbook of Biochemistry for Medical Students, 6th ed. (Jaypee Brothers Medical Publishers (Vasudevan DM, Sreekumari S, Vaidyanathan K), 2011).

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