Function

Mnemonic

Active forms of Niacin are NAD+ and NADP+.

• Cofactor for redox reactions (e.g., alcohol dehydrogenase, isocitrate dehydrogenase, G6PD)

Therapeutic use

• Dyslipidemia: Niacin lowers VLDL and increases HDL serum levels (See Lipid-lowering agents)

---

Vitamin B3 deficiency

Etiology

• Malnutrition
• Heavy drinking
• Conditions associated with tryptophan deficiency
  • Hartnup disease: decreased renal and intestinal tryptophan absorption
  • Carcinoid syndrome (if metabolically active): increased tryptophan metabolism
• Vitamin B6 deficiency (e.g., due to treatment with isoniazid): decreased niacin synthesis from tryptophan
• Chronic consumption of grains that have not been processed by nixtamalization (common cause in developing countries)

---

Pathophysiology

---

Clinical features

• Glossitis
• Pellagra (caused by severe deficiency)
  • Characteristic dermatitis
    • Circular broad collar rash on the neck (Casal necklace); affects dermatomes C3 and C4
    • Hyperpigmented skin lesions in sun-exposed areas (especially on the limbs)
  • Diarrhea and vomiting
  • Neurologic symptoms (e.g, dementia, hallucinations, anxiety, insomnia, encephalopathy)

Mnemonic

• 3 typical features of severe vitamin B₃ Deficiency: Dermatitis, Diarrhea, and Dementia.
• 3 for tree: dermatitis, dementia

---

Diagnostics

---

Treatment

---

Vitamin B3 toxicity

• Facial flushing: due to prostaglandin release and NOT due to histamine (typically seen when niacin therapy is started, can be avoided by coadministration of aspirin)
• Hyperuricemia, podagra
  • Niacin decreases renal uric acid excretion.
• Hyperglycemia