Question
Classify vitamins into fat-soluble and water-soluble groups. For each vitamin, list its chemical name, dietary source, and the deficiency disease it causes. Why can fat-soluble vitamins cause toxicity but water-soluble ones rarely do?
(NEET + CBSE Board — recall + reasoning)
Solution — Step by Step
Vitamins are classified based on solubility:
- Fat-soluble: A, D, E, K — stored in liver and fat tissue
- Water-soluble: B-complex (B₁, B₂, B₃, B₆, B₇, B₉, B₁₂) and C — excreted in urine if in excess
| Vitamin | Chemical Name | Source | Deficiency Disease |
|---|---|---|---|
| A | Retinol | Carrot, liver, fish oil | Night blindness (Nyctalopia), Xerophthalmia |
| D | Calciferol | Sunlight, fish, eggs | Rickets (children), Osteomalacia (adults) |
| E | Tocopherol | Vegetable oils, nuts, seeds | Reproductive failure, muscle weakness |
| K | Phylloquinone | Green leafy vegetables, gut bacteria | Delayed blood clotting, haemorrhage |
| Vitamin | Chemical Name | Source | Deficiency Disease |
|---|---|---|---|
| B₁ | Thiamine | Whole grains, legumes | Beriberi |
| B₂ | Riboflavin | Milk, eggs, liver | Cheilosis (cracked lips) |
| B₃ | Niacin | Meat, peanuts | Pellagra (3 Ds: Dermatitis, Diarrhea, Dementia) |
| B₅ | Pantothenic acid | Widely available | Rare — fatigue, burning feet |
| B₆ | Pyridoxine | Cereals, meat | Anaemia, convulsions |
| B₇ | Biotin | Egg yolk, liver | Dermatitis, hair loss |
| B₉ | Folic acid | Leafy vegetables | Megaloblastic anaemia, neural tube defects |
| B₁₂ | Cyanocobalamin | Animal products only | Pernicious anaemia |
| C | Ascorbic acid | Citrus fruits, amla | Scurvy (bleeding gums, loose teeth) |
Fat-soluble vitamins dissolve in lipids and are stored in the liver and adipose tissue. If you consume them in excess, they accumulate over time instead of being excreted — leading to hypervitaminosis (toxicity). Vitamin A excess causes headaches, liver damage; Vitamin D excess causes hypercalcemia.
Water-soluble vitamins dissolve in water and any excess is quickly excreted through urine. The body cannot store them in large quantities, so toxicity is extremely rare.
graph TD
A[Vitamins] --> B["Fat-Soluble: A, D, E, K"]
A --> C["Water-Soluble: B-complex, C"]
B --> B1["Stored in liver/fat"]
B --> B2["Can cause toxicity"]
C --> C1["Excreted in urine"]
C --> C2["Rarely toxic"]
B --> B3["A: Night blindness"]
B --> B4["D: Rickets"]
C --> C3["B1: Beriberi"]
C --> C4["C: Scurvy"]
style A fill:#fbbf24,stroke:#000,stroke-width:2px
style B fill:#f9a8d4,stroke:#000
style C fill:#93c5fd,stroke:#000Why This Works
Vitamins are organic compounds needed in trace amounts for metabolic reactions — they often act as coenzymes. The fat vs. water solubility determines their pharmacokinetics: storage, excretion, and potential for toxicity.
The deficiency diseases are so specific because each vitamin plays a unique biochemical role. Vitamin C is needed for collagen synthesis — without it, connective tissue breaks down (hence bleeding gums in scurvy). Vitamin D regulates calcium absorption — without it, bones cannot mineralise (hence rickets).
Common Mistake
Students often confuse Beriberi (B₁/Thiamine deficiency) with Pellagra (B₃/Niacin deficiency). Remember: BeriBeri = B₁, Pellagra = B₃ (P for “3 Ds” — Dermatitis, Diarrhea, Dementia). Also, B₁₂ is found ONLY in animal products — vegetarians and vegans are at risk of deficiency.
NEET mnemonic for fat-soluble vitamins: “ADEK” — the only four that dissolve in fat. Everything else (all B vitamins and C) is water-soluble. This single fact helps you answer classification questions in under 10 seconds.