Step by Step
Col
Collagen synthesis — the key role
Vitamin C (ascorbic acid) is essential for collagen synthesis. It serves as a cofactor for prolyl hydroxylase and lysyl hydroxylase — enzymes that hydroxylate proline and lysine residues in procollagen. Hydroxylation cross-links collagen fibers, giving connective tissue its strength. Without vitamin C, abnormal collagen is produced → connective tissue weakness throughout the body.
Memory trick: Vitamin C = collagen's carpenter. Without the carpenter, the building (collagen) falls apart.
Scu
Scurvy — the deficiency disease
Scurvy develops after ~3 months of vitamin C deficiency. Classic signs: bleeding gums (gingival hemorrhage), perifollicular hemorrhages (bleeding around hair follicles), corkscrew hairs, poor wound healing, easy bruising. Systemic: anemia (iron absorption impaired), joint pain, emotional changes. Classic in sailors on long voyages without fresh produce — solved by limes/lemons (hence 'limeys').
Memory trick: Scurvy = 'Scars Crumble Under Vitamin deficiency.' Collagen falls apart.
Anti
Antioxidant and other functions
Beyond collagen: Vitamin C is a potent water-soluble antioxidant — donates electrons to neutralize free radicals. Enhances non-heme iron absorption (reduces Fe³⁺ → Fe²⁺ in the intestine for better absorption). Regenerates vitamin E (lipid-soluble antioxidant). Involved in carnitine synthesis, norepinephrine synthesis, and immune function.
Src
Sources and RDA
Major sources: citrus fruits, kiwi, strawberries, bell peppers, broccoli. RDA: ~90 mg/day (men), ~75 mg/day (women). Smokers need ~35 mg/day extra (smoking increases oxidative stress). Cooking destroys vitamin C (heat-labile). Excess is excreted in urine — generally safe, but very high doses can cause kidney stones (oxalate) and GI upset.
Applied Walkthrough
1
A 17th-century sailor on a 6-month voyage eating only hardtack and salt pork develops swollen, bleeding gums and easy bruising — classic scurvy from 3+ months without vitamin C.
2
His body cannot hydroxylate proline/lysine → defective collagen in blood vessel walls → vessels become fragile → hemorrhage.
3
James Lind's 1747 trial: sailors given citrus recovered from scurvy within days. The British Navy eventually mandated lime rations — eliminating scurvy from the fleet.
4
A modern patient on a restrictive diet presents with perifollicular hemorrhages and poor wound healing after surgery — vitamin C deficiency should be high on the differential.
Exam Application
Exams test vitamin C's role as a cofactor for prolyl/lysyl hydroxylase in collagen synthesis, the clinical features of scurvy (bleeding gums, perifollicular hemorrhages, poor wound healing), vitamin C's role in iron absorption (reduces Fe³⁺ to Fe²⁺), and its antioxidant function (regenerates vitamin E). All are frequently tested.
⚠ Common Trap
Students think vitamin C directly makes collagen — it doesn't. It is a cofactor for the hydroxylases that modify procollagen AFTER translation. The collagen protein is made normally; the problem is it can't be properly cross-linked without hydroxylated proline and lysine. Also: iron deficiency anemia can be worsened by vitamin C deficiency (impaired iron absorption).
✓ Quick Self-Check
1. What is the biochemical role of vitamin C in collagen synthesis?
Cofactor for prolyl hydroxylase and lysyl hydroxylase — enzymes that hydroxylate proline and lysine residues to allow collagen cross-linking.
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2. What are three classic signs of scurvy?
Bleeding gums (gingival hemorrhage), perifollicular hemorrhages, and poor wound healing.
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3. How does vitamin C enhance iron absorption?
It reduces Fe³⁺ (ferric) to Fe²⁺ (ferrous) in the intestine — Fe²⁺ is more readily absorbed by enterocytes.
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4. How does vitamin C relate to vitamin E?
Vitamin C (water-soluble) regenerates vitamin E (fat-soluble) after vitamin E has quenched a free radical — they work synergistically as antioxidants.
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5. How long does it take to develop scurvy?
Approximately 3 months of vitamin C deficiency.
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