Learning Objectives
- Identify the B-complex vitamins and their active coenzyme forms.
- Contrast the storage and excretion of water-soluble vs. fat-soluble vitamins.
- Recognize the clinical triad of B-complex deficiency.
- Understand the unique hepatic storage of B9 (Folate) and B12 (Cobalamin).
1. The Water-Soluble Profile
Water-soluble vitamins (the B-complex group and Vitamin C) generally “wash out” of the body easily. Because they are excreted in the urine, toxicity is rare, but frequent dietary intake is necessary.
- Exception to the Rule: While most are not stored, two vitamins have significant hepatic reserves:
- Vitamin B12: Stored in the liver for 3–4 years.
- Vitamin B9: Stored in the liver for 3–4 months.
2. B-Complex Vitamins & Coenzymes
These vitamins function primarily as precursors to essential coenzymes in metabolic pathways like the TCA cycle and glycolysis.
| Vitamin | Active Coenzyme Form |
|---|---|
| B1 (Thiamine) | TPP (Thiamine pyrophosphate) |
| B2 (Riboflavin) | FAD, FMN |
| B3 (Niacin) | NAD+, NADP+ |
| B5 (Pantothenic acid) | CoA (Coenzyme A) |
| B6 (Pyridoxine) | PLP (Pyridoxal phosphate) |
| B7 (Biotin) | Biotin (Carboxylation cofactor) |
| B9 (Folate) | THF (Tetrahydrofolate) |
| B12 (Cobalamin) | Methylcobalamin |
| C (Ascorbic acid) | Ascorbate (Redox cofactor) |
3. Deficiency Manifestations
General B-complex deficiencies often present with a common set of symptoms affecting rapidly dividing cells in the skin and GI tract:
- Dermatitis: Skin inflammation/rash.
- Glossitis: Inflammation of the tongue (smooth, beefy red tongue).
- Diarrhea: Malabsorption due to intestinal mucosal atrophy.
Activity