OVERVIEW OF B3 DEFICIENCY

  • Vitamin B3 (niacin): Exists primarily as nicotinic acid and nicotinamide.
  • Key dietary sources:
    • Meats (especially liver)
    • Yeasts
    • Whole-grain cereals
    • Legumes
    • Seeds
  • Geographic distribution: Historically linked to diets based heavily on maize/corn; still seen in parts of India, China, and Africa.
  • Causes in developed countries:
    • Gastrointestinal malabsorptive disorders
    • Anorexia nervosa
    • Alcoholism

BIOCHEMICAL ROLE

  • Niacin (nicotinic acid & nicotinamide) is converted (along with tryptophan) to form:
    • NAD (nicotinamide adenine dinucleotide)
    • NADP (nicotinamide adenine dinucleotide phosphate)
  • NAD & NADP:
    • Vital in redox reactions and hydrogen transport
    • Essential for synthesis and metabolism of carbohydrates, fats, and proteins
  • Absorption: Occurs in jejunum and ileum.
  • Tissue uptake: Rapidly taken up by liver, kidney, RBCs.
  • Storage/Use: Intracellularly converted to NAD/NADP; stored mostly in liver & muscle (high metabolic activity tissues).

PELLAGRA

  • Definition: A nutritional deficiency disorder caused by insufficient intake of niacin.
  • Name origin: “Raw skin,” first described in 1735 by Casál in Spanish peasants subsisting on maize-based diets.
  • Classic triad: Dermatitis, diarrhea, dementia (“3 D’s”).

Clinical Features

  1. Dermatitis:
    • Photosensitivity with symmetric lesions; sharp borders between affected/unaffected skin.
    • Common on extensor surfaces (hands, arms, feet) → “glove-and-stocking” distribution.
    • Casál necklace: circumferential lesion around neck.
    • Facial lesions may appear over the alae of the nose and forehead.
    • Intertriginous and moist areas also commonly affected.
    • Lesions evolve from sunburn-like erythema → reddish-brown, rough, scaly patches → central desquamation revealing thickened, red skin.
    • Chronic changes: skin may remain roughened and pigmented.
  2. Stomatitis & GI Involvement:
    • Sore mouth, angular cheilitis.
    • Indigestion, bright red tongue with flattened papillae.
    • Diarrhea (watery; may contain blood or pus).
  3. Neurologic/Psychiatric:
    • Can present with encephalopathy mimicking mental illness (e.g., depression, suicidal tendencies).
    • Anxiety, disorientation, hallucinations, confusion, delirium, dementia, and coma.

DIAGNOSIS

  • Clinical recognition of dermatitis, diarrhea, dementia is key.
  • Lab confirmation: Blood niacin concentration (typical normal range is approximately 0.50–8.45 μg/mL in adults).

PREVENTION

  • Recommended Daily Allowance (RDA):
    • ~16 niacin equivalents/day (men)
    • ~14 niacin equivalents/day (women)
    • ~18 niacin equivalents/day during pregnancy, 17 niacin equivalents/day during lactation
  • One niacin equivalent = 1 mg niacin or ~6 mg tryptophan.
  • High-risk groups: Individuals who have had malabsorptive procedures or are on renal dialysis may need extra supplementation.
  • Dietary advice: A balanced diet that includes meat, yeasts, whole grains, legumes, seeds usually provides sufficient niacin.

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