USMLE

Vitamin B3 (Niacin) Deficiency and Excess

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Vitamins
  1. Vitamin B1 (Thiamine) Biochemistry
  2. Vitamin B1 (Thiamine) Deficiency
  3. Vitamin B2 (Riboflavin)
  4. Vitamin B3 (Niacin) Biochemistry
  5. Vitamin B3 (Niacin) Deficiency and Excess
  6. Hartnup Disease
  7. Vitamin B5 (Pantothenic Acid)
  8. Vitamin B6 (Pyridoxine)
  9. Vitamin B7 (Biotin)
  10. Vitamin B9 (Folate)
  11. Vitamin B12 (Cobalamin) Biochemistry
  12. Vitamins B9 and B12 Deficiencies
  13. Vitamin A (Retinol) Biochemistry
  14. Vitamin A (Retinol) Deficiency and Excess
  15. Vitamin C (Ascorbic Acid) Biochemistry
  16. Vitamin C (Ascorbic Acid) Deficiency and Excess
  17. Vitamin D Biochemistry
  18. Vitamin D Deficiency and Excess
  19. Vitamin E (Tocopherol/Tocotrienol)
  20. Vitamin K Biochemistry
  21. Vitamin K Deficiency
  22. Zinc
  23. Kwashiorkor and Marasmus

Summary

Niacin (Vitamin B3) imbalances in the body may present as deficiency or excess. Mild niacin deficiency presents with glossitis, and severe deficiency is characterized by the clinical syndrome of pellagra, which includes the constellation of dermatitis, dementia, diarrhea, and potentially death. Niacin excess is rare, and is typically observed after administering niacin to treat lipid disorders. Symptoms of excess notably include facial flushing responsive to aspirin, flares of gout (hyperuricemia), and occasionally, hyperglycemia (high blood sugar).

Key Points

  • Niacin (Vitamin B3) Deficiency
    • Seen in malnourished patients like alcoholics (developed countries), and in populations who mainly eat corn (developing countries)
    • Mild deficiency leads to glossitis
    • Severe deficiency causes pellagra
      • Diarrhea
        • Secondary to atrophy of columnar epithelium of GI tract
      • Dementia
      • Dermatitis
        • Bilateral, symmetric scaly rash on sun-exposed surfaces
        • Broad collar rash in the C3-C4 dermatome (Casal necklace)
  • Niacin (Vitamin B3) Excess
    • Cutaneous flushing
      • induced by prostaglandins (not histamine)
        • reduce by treating with aspirin
    • Hyperuricemia/gout
      • Podagra (swollen first metatarsophalangeal joint) is common
    • Hyperglycemia


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