Vitamins
On this page 18 sections
Fat Soluble
| Vitamin & Chemical Name | Key Functions & MCQ Notes | Main Sources | Deficiency Manifestations |
| Vitamin A (Retinol, Retinal, Retinoic acid) | • Vision (constituent of rhodopsin) • Epithelial tissue maintenance & immunity • Teratogenic in excess | Liver, fish liver oils, carrots, dark leafy greens (beta-carotene) | • Night blindness (Nyctalopia - earliest sign) • Xerophthalmia & Bitot's spots • Keratomalacia • Follicular hyperkeratosis |
| Vitamin D (D₂: Ergocalciferol, D₃: Cholecalciferol) | • Calcium & phosphate absorption • Active form: 1,25\-(OH)_2\D_3 (Calcitriol) • Activated by hydroxylation in liver (25) & kidney (1) | Sunlight exposure, fatty fish, egg yolk, fortified milk Cod Liver oil | • Rickets in children (bow legs, rachitic rosary) • Osteomalacia in adults (soft bones) • Hypocalcemia |
| Vitamin E (Tocopherol) | • Major lipid-soluble antioxidant • Protects cell membranes & RBCs from peroxidation | Vegetable oils, nuts, seeds, wheat germ | • Hemolytic anemia (especially in premature infants) • Neurological deficits (spinocerebellar ataxia, muscle weakness) |
| Vitamin K (K₁: Phylloquinone, K₂: Menaquinone) | • Essential for γ-carboxylation of Clotting Factors II, VII, IX, X and Proteins C & S • Inhibited by Warfarin | Green leafy vegetables; synthesized by gut flora | • Prolonged Prothrombin Time (PT) & Bleeding Time • Hemorrhagic disease of the newborn (sterile gut at birth) |
Vitamin A
Vitamin A supports retinal function and normal epithelial differentiation.
- Retinal is required for visual phototransduction.
- Retinoic acid regulates gene transcription and epithelial differentiation.
- Deficiency can cause night blindness, conjunctival xerosis and Bitot spots.
- Severe deficiency can cause corneal damage and keratomalacia.
Clinical correlation: Vitamin A deficiency may affect oral and respiratory epithelium as well as vision.
Vitamin D
Vitamin D promotes intestinal calcium and phosphate absorption and supports normal bone mineralization.
| Deficiency | Typical manifestation |
|---|---|
| Children | Rickets |
| Adults | Osteomalacia |
| Severe deficiency | Bone pain, muscle weakness and increased fracture risk |
Vitamin D is activated through hydroxylation in the liver and kidneys. The kidney produces 1,25-dihydroxyvitamin D (calcitriol), the active hormonal form.
Vitamin E
Vitamin E protects cell membranes from oxidative damage.
Deficiency may cause:
- Hemolytic anemia.
- Peripheral neuropathy.
- Ataxia and impaired proprioception, particularly in severe deficiency or malabsorption.
Vitamin K
Vitamin K is required for gamma-carboxylation of glutamate residues in coagulation proteins.
Important vitamin K-dependent proteins include:
- Factors II, VII, IX and X.
- Proteins C and S.
Deficiency impairs normal clotting and can prolong PT/INR, often early because factor VII has a relatively short half-life.
Remember: Vitamin K deficiency affects clotting factor function, not simply their production.
Water soluble
| Vitamin & Chemical Name | Key Functions & MCQ Notes | Main Sources | Deficiency Manifestations |
| Vitamin B₁ (Thiamine) | • Coenzyme: TPP (Thiamine pyrophosphate) • Key enzymes: Pyruvate dehydrogenase, Transketolase | Whole grains, legumes, pork, unpolished rice | • Beriberi: - Dry: Peripheral neuropathy - Wet: High-output heart failure / edema • Wernicke-Korsakoff syndrome (triad: ataxia, confusion, ophthalmoplegia; seen in chronic alcoholism) |
| Vitamin B₂ (Riboflavin) | • Coenzymes: FAD, FMN (redox reactions) • Derived from ribitol + flavin | Milk, eggs, liver, green vegetables | • Cheilosis (cracks at corners of mouth) • Angular stomatitis & Glossitis (magenta tongue) • Corneal neovascularization |
| Vitamin B₃ (Niacin / Nicotinic Acid) | • Coenzymes: NAD⁺, NADP⁺ • Synthesized from Tryptophan (requires $B_6$) • Excess causes cutaneous flushing | Meat, fish, poultry, grains, legumes | • Pellagra (3 Ds): - Dermatitis (Casal's necklace pattern) - Diarrhea - Dementia (Can lead to Death if untreated) |
| Vitamin B₅ (Pantothenic Acid) | • Component of Coenzyme A (CoA) & Fatty Acid Synthase | Widely distributed in foods ("pan" = everywhere) | • "Burning feet" syndrome (paresthesias) • Adrenal insufficiency, alopecia |
| Vitamin B₆ (Pyridoxine) | • Active form: PLP (Pyridoxal phosphate) • Required for transamination, decarboxylation, & heme synthesis • Elevated requirement with high protein intake & Isoniazid (INH) therapy | Meat, bananas, whole grains, nuts | • Peripheral neuropathy (prevented by giving B_6 with INH) • Microcytic sideroblastic anemia • Convulsions / Seizures |
| Vitamin B₇ (Biotin) | • Coenzyme for Carboxylation reactions (e.g., Pyruvate carboxylase) • Antagonized by Avidin in raw egg whites | Egg yolk, liver, produced by intestinal bacteria | • Dermatitis, alopecia, muscle pain, paresthesias |
| Vitamin B₉ (Folic Acid / Folate) | • Active form: THF (Tetrahydrofolate) • One-carbon transfers (DNA synthesis) • No neurological signs (unlike B_12 | Green leafy vegetables ("folium"), legumes, liver | • Megaloblastic anemia (hypersegmented neutrophils) • Neural tube defects (spina bifida in fetus) |
| Vitamin B₁₂ (Cobalamin) | • Contains Cobalt; required for DNA synthesis & myelin maintenance • Requires Intrinsic Factor (IF) from parietal cells for absorption in terminal ileum | Meat, fish, eggs, dairy (absent in plants / strict vegans) | • Pernicious anemia (Megaloblastic anemia + IF deficiency) • Subacute combined degeneration (SCD) of spinal cord (neurological damage) |
| Vitamin C (Ascorbic Acid) | • Hydroxylation of Proline & Lysine in collagen synthesis • Antioxidant; enhances non-heme iron absorption | Citrus fruits, tomatoes, berries, broccoli, peppers | • Scurvy: - Bleeding / swollen gums, loose teeth - Poor wound healing - Perifollicular hemorrhages & petechiae |
Vitamin B1 — Thiamine
Thiamine is converted into thiamine pyrophosphate (TPP), a cofactor for several important enzymes.
Major TPP-dependent enzymes:
- Pyruvate dehydrogenase.
- α-Ketoglutarate dehydrogenase.
- Branched-chain α-ketoacid dehydrogenase.
- Transketolase.
| Deficiency syndrome | Key findings |
|---|---|
| Dry beriberi | Peripheral neuropathy and muscle wasting |
| Wet beriberi | Cardiovascular dysfunction and edema |
| Wernicke encephalopathy | Confusion, ataxia and ophthalmoplegia |
| Korsakoff syndrome | Memory impairment and confabulation |
Exam tip: Give thiamine before or alongside glucose in patients at risk of deficiency, particularly those with severe malnutrition or chronic alcohol use.
Vitamin B2 — Riboflavin
Riboflavin forms FAD and FMN, which participate in oxidation-reduction reactions.
Deficiency may cause angular cheilitis, glossitis and inflammation of oral mucosa.
Vitamin B3 — Niacin
Niacin is required for synthesis of NAD and NADP.
Pellagra is classically associated with the 3 Ds:
- Dermatitis.
- Diarrhea.
- Dementia.
Severe untreated deficiency can be fatal.
Vitamin B6 — Pyridoxine
Vitamin B6, in its active form pyridoxal phosphate (PLP), acts as a cofactor in amino acid metabolism, neurotransmitter synthesis and heme production.
Deficiency may cause neuropathy, seizures and sideroblastic anemia.
Drug association: Isoniazid can cause B6 deficiency; pyridoxine supplementation is used in appropriate patients to prevent or treat it.
Vitamin B9 versus B12
| Feature | Folate (B9) | Cobalamin (B12) |
|---|---|---|
| Main role | DNA synthesis and one-carbon transfer | DNA synthesis and neurologic function |
| Deficiency anemia | Megaloblastic | Megaloblastic |
| Neurologic dysfunction | Not characteristic | May be prominent |
| Homocysteine | Increased | Increased |
| Methylmalonic acid | Usually normal | Increased |
| Major dietary sources | Leafy vegetables, legumes and fortified grains | Animal-derived foods and fortified foods |
Critical exam point: Folate can correct the anemia of B12 deficiency without preventing progressive neurologic injury. Assess for B12 deficiency before treating unexplained megaloblastic anemia with folate alone.
Vitamin C — Ascorbic acid
Vitamin C is needed for hydroxylation of proline and lysine during collagen synthesis.
Deficiency causes scurvy, characterized by:
- Bleeding gums.
- Petechiae and perifollicular hemorrhage.
- Poor wound healing.
- Easy bruising.
- Impaired collagen formation.
Clinical correlations
| Clinical clue | Vitamin to consider |
|---|---|
| Night blindness | A |
| Rickets or osteomalacia | D |
| Hemolysis and neuropathy | E |
| Bleeding with prolonged PT | K |
| Wernicke encephalopathy | B1 |
| Pellagra | B3 |
| Isoniazid-associated neuropathy | B6 |
| Megaloblastic anemia with neurologic signs | B12 |
| Megaloblastic anemia without typical neurologic signs | Folate |
| Bleeding gums and poor wound healing | C |
Vitamin D Synthesis
7-Dehydrocholesterol (Skin)
│ UVB Light (Sunlight)
▼
Cholecalciferol (Vitamin D₃)
│ 25-Hydroxylase (LIVER)
▼
25-Hydroxyvitamin D₃ / Calcidiol
│ 1-α-Hydroxylase (KIDNEY) [Stimulated by PTH]
▼
1,25-Dihydroxyvitamin D₃ / Calcitriol (ACTIVE FORM)Step 1: Skin Synthesis (Photolysis)
- Precursor: 7-Dehydrocholesterol (present in the Malpighian layer of the epidermis).
- Trigger: Ultraviolet B (UVB) radiation from sunlight converts 7-dehydrocholesterol into Pre-vitamin D₃, which isomerizes to Cholecalciferol (Vitamin D₃).
- (Dietary forms: {D}_3 comes from animal sources; {D}_2 / Ergocalciferol comes from plants/fungi).
Step 2: 1st Hydroxylation — LIVER (Storage Form)
- Location: Liver (Hepatocytes).
- Enzyme: 25-Hydroxylase (CYP2R1).
- Product: 25-Hydroxyvitamin {D}_3 [25-(OH){D}_3] — also known as Calcidiol.
- MCQ Note: Calcidiol is the major circulating & storage form used to measure serum Vitamin D levels in clinical blood tests.
Step 3: 2nd Hydroxylation — KIDNEY (Active Form)
- Location: Kidney (Proximal Convoluted Tubule cells).
- Enzyme: 1-alpha-Hydroxylase (CYP27B1).
- Product: 1,25-Dihydroxyvitamin {D}_3 [1,25 {-(OH)}_2 {D}_3] — also known as Calcitriol (the physiologically active hormone).
Regulation of 1-alpha-Hydroxylase (High-Yield MCQ Points):
- Stimulated by:
- PTH (Parathyroid Hormone) — released during low plasma {Ca}^2+
- Hypophosphatemia (low serum Phosphate)
- Inhibited by:
- High serum Calcium
- High serum Phosphate
- FGF-23 (Fibroblast Growth Factor 23)
- High levels of Calcitriol itself (Negative feedback)