## Vitamin C (Ascorbic Acid) — Properties and Deficiency ### Chemical Nature and Storage **Key Point:** Vitamin C is a **water-soluble vitamin**, NOT fat-soluble. It is poorly stored in the body and must be supplied regularly through diet. Excess intake is excreted in urine. ### Biochemical Role in Collagen Synthesis 1. Acts as a cofactor for prolyl and lysyl hydroxylase enzymes 2. Hydroxylates proline → hydroxyproline and lysine → hydroxylysine 3. These hydroxylated residues are essential for collagen cross-linking and stability 4. Without adequate vitamin C, collagen is structurally weak and defective ### Manifestations of Scurvy (Vitamin C Deficiency) | Feature | Mechanism | |---------|----------| | Bleeding gums, petechiae, ecchymoses | Defective collagen in blood vessel basement membrane → fragility | | Poor wound healing | Impaired collagen synthesis and remodeling | | Follicular hyperkeratosis | Defective collagen around hair follicles | | Anemia | Impaired iron absorption (vitamin C enhances non-heme iron absorption) | | Bone pain, subperiosteal hemorrhages | Defective osteoid matrix (collagen-dependent) | | Loose teeth, bleeding around teeth | Periodontal collagen breakdown | **High-Yield:** Vitamin C is water-soluble and rapidly depleted; body stores last only 1–3 months without dietary intake. ### Why Option 4 is Wrong Vitamin C is **water-soluble**, not fat-soluble. Fat-soluble vitamins (A, D, E, K) are stored in adipose tissue and liver; water-soluble vitamins (B complex, C) are not stored and must be replenished daily. **Clinical Pearl:** In Indian pediatric practice, scurvy is rare but can occur in children with restricted diets (e.g., exclusive milk feeding, no fruits/vegetables). Diagnosis is clinical; plasma ascorbic acid <0.2 mg/dL confirms deficiency. [cite:Park 26e Ch 7]
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