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
- 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.
- Stomatitis & GI Involvement:
- Sore mouth, angular cheilitis.
- Indigestion, bright red tongue with flattened papillae.
- Diarrhea (watery; may contain blood or pus).
- 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.