The Hook: Tiny Molecules, Huge Impact
Sailors once died from scurvy on long voyages - cured by lemon juice (Vitamin C)! Night blindness from Vitamin A deficiency, rickets from lack of Vitamin D, beriberi from no Vitamin B₁. Just milligrams of these molecules make the difference between health and disease. Why do we need vitamins? And why can’t our body make them?
Here’s the JEE question: Why are some vitamins stored in body (A, D, E, K) while others need daily intake (B, C)? What makes water-soluble vitamins different from fat-soluble ones?
The Core Concept
What are Vitamins?
Vitamins = Organic compounds required in small amounts for normal metabolic functions
Characteristics:
- Essential nutrients (body cannot synthesize in adequate amounts)
- Required in small quantities (milligrams or micrograms)
- Organic molecules (contain carbon)
- Must be obtained from diet
- Deficiency causes specific diseases
Etymology: “Vital amines” (originally thought all were amines)
Classification of Vitamins
Based on Solubility
1. Fat-Soluble Vitamins:
- A, D, E, K
- Dissolve in fats and oils
- Stored in body (liver, adipose tissue)
- Excess can accumulate → toxicity possible
- Do NOT need daily intake
2. Water-Soluble Vitamins:
- B-complex and C
- Dissolve in water
- Not stored (excreted in urine)
- No toxicity (excess eliminated)
- Need regular intake
Fat-soluble: “ADEK (sounds like ‘a deck’ of cards)”
- A, D, E, K
- Stored in body
- Can be toxic in excess
Water-soluble: “BC vitamins need B Consumed daily”
- B-complex and C
- Not stored
- Need daily intake
JEE Tip: Solubility determines storage and toxicity!
Fat-Soluble Vitamins
Vitamin A (Retinol)
Chemical name: Retinol
Sources:
- Animal: Liver, fish liver oils, milk, butter, egg yolk
- Plant (as β-carotene): Carrots, spinach, mangoes, papaya
- Note: β-carotene = provitamin A (converted to Vitamin A in body)
Functions:
- Vision: Component of rhodopsin (visual pigment)
- Skin health: Maintains epithelial tissues
- Growth: Bone and tooth development
- Immunity: Supports immune function
Deficiency diseases:
- Night blindness (Nyctalopia) - cannot see in dim light
- Xerophthalmia - dryness of eyes, can lead to blindness
- Keratomalacia - corneal damage
- Dry, scaly skin
Hypervitaminosis (excess):
- Liver damage
- Bone pain
- Skin changes
- Teratogenic (birth defects if during pregnancy)
Mechanism:
Step 1: β-carotene (from carrots) → Vitamin A (retinol)
Step 2: Retinol → Retinal (aldehyde form)
Step 3: Retinal + Opsin protein → Rhodopsin (visual purple)
Step 4: Light hits rhodopsin:
$$\text{Rhodopsin} \xrightarrow{\text{light}} \text{Retinal} + \text{Opsin}$$Step 5: This change triggers nerve impulse → vision!
In darkness: Rhodopsin regenerates (needs Vitamin A)
Deficiency: Cannot regenerate rhodopsin → night blindness
JEE Fact: This is why carrots are said to improve vision (provide β-carotene)!
Vitamin D (Calciferol)
Chemical names:
- Vitamin D₂: Ergocalciferol
- Vitamin D₃: Cholecalciferol (more active)
Sources:
- Sunlight: UV radiation converts 7-dehydrocholesterol in skin → Vitamin D₃
- Food: Fish liver oils, eggs, milk, butter
Unique feature: Can be synthesized in skin with sunlight exposure!
Functions:
- Calcium absorption: Increases Ca²⁺ absorption from intestine
- Bone mineralization: Helps deposit Ca and P in bones
- Bone health: Prevents bone disorders
Deficiency diseases:
- Rickets (children) - soft, deformed bones, bow legs
- Osteomalacia (adults) - soft bones, bone pain
- Osteoporosis (elderly) - brittle bones
Hypervitaminosis:
- Hypercalcemia (too much Ca²⁺ in blood)
- Kidney stones
- Calcium deposits in soft tissues
Vitamin E (Tocopherol)
Chemical name: α-Tocopherol
Sources:
- Vegetable oils (wheat germ, sunflower, corn)
- Nuts, seeds
- Green leafy vegetables
- Whole grains
Functions:
- Antioxidant: Protects cell membranes from oxidative damage
- Free radical scavenger: Neutralizes reactive oxygen species
- Prevents lipid peroxidation in cell membranes
Deficiency:
- Rare (body stores vitamin E)
- Hemolytic anemia (RBC breakdown)
- Nerve damage (in severe cases)
- Muscle weakness
Toxicity: Low (even at high doses)
Vitamin K (Phylloquinone)
Chemical names:
- Vitamin K₁: Phylloquinone (from plants)
- Vitamin K₂: Menaquinone (from bacteria)
Sources:
- Green leafy vegetables (spinach, kale, cabbage)
- Gut bacteria synthesize Vitamin K₂
- Liver, eggs
Functions:
- Blood clotting: Essential for synthesis of clotting factors (II, VII, IX, X)
- Bone metabolism: Helps in bone matrix formation
Deficiency:
- Hemorrhage (excessive bleeding)
- Delayed blood clotting
- Rare (gut bacteria provide sufficient amounts)
- Common in newborns (given Vitamin K injection at birth)
Q: Why are newborns given Vitamin K injection shortly after birth?
Answer:
Reasons:
1. Sterile gut:
- Newborn intestines don’t have bacteria yet
- Gut bacteria synthesize Vitamin K
- No bacterial source at birth
2. Low placental transfer:
- Vitamin K doesn’t cross placenta well
- Baby has low stores at birth
3. Low in breast milk:
- Mother’s milk has insufficient Vitamin K
4. Risk of hemorrhage:
- Without Vitamin K: poor blood clotting
- Hemorrhagic disease of newborn
- Can cause brain bleeding (fatal)
Solution: Vitamin K injection (phylloquinone)
- Prevents bleeding disorders
- Given within hours of birth
- Provides protection until gut bacteria establish
JEE Tip: Vitamin K = “Koagulation vitamin” (German spelling)
Interactive Demo: Visualize Vitamin Structures
Explore the molecular structures of fat-soluble and water-soluble vitamins.
Water-Soluble Vitamins
B-Complex Vitamins
Vitamin B₁ (Thiamine)
Sources:
- Whole grains, legumes, nuts
- Pork, yeast
- Fortified cereals
Functions:
- Coenzyme in carbohydrate metabolism
- Energy production from glucose
- Nerve function
Deficiency:
- Beriberi:
- Wet beriberi: Heart failure, edema
- Dry beriberi: Nerve damage, muscle wasting
- Wernicke-Korsakoff syndrome (alcoholics)
Vitamin B₂ (Riboflavin)
Sources:
- Milk, eggs, liver
- Green vegetables
- Fortified cereals
Functions:
- Component of FAD (flavin adenine dinucleotide)
- Coenzyme in redox reactions
- Energy metabolism
Deficiency:
- Ariboflavinosis:
- Cracks at corner of mouth (cheilosis)
- Inflamed tongue (glossitis)
- Skin disorders
Vitamin B₃ (Niacin)
Chemical names: Nicotinic acid, Nicotinamide
Sources:
- Meat, fish, peanuts
- Whole grains
- Can be synthesized from tryptophan (amino acid)
Functions:
- Component of NAD⁺ and NADP⁺
- Coenzyme in oxidation-reduction reactions
- Energy metabolism
Deficiency:
- Pellagra: “3D disease”
- Dermatitis (skin inflammation)
- Diarrhea
- Dementia
- Can be fatal if untreated
Vitamin B₅ (Pantothenic Acid)
Sources:
- Widespread in foods (name from Greek “pantothen” = everywhere)
- Meat, whole grains, legumes
Functions:
- Component of Coenzyme A (CoA)
- Fatty acid metabolism
- Energy production
Deficiency:
- Rare (present in most foods)
- Fatigue, numbness
Vitamin B₆ (Pyridoxine)
Sources:
- Meat, fish, poultry
- Bananas, potatoes
- Fortified cereals
Functions:
- Coenzyme in amino acid metabolism
- Hemoglobin synthesis
- Neurotransmitter synthesis
Deficiency:
- Anemia
- Dermatitis
- Depression, confusion
Vitamin B₇ (Biotin)
Sources:
- Egg yolk, liver, nuts
- Gut bacteria synthesize biotin
Functions:
- Coenzyme in carboxylation reactions
- Fatty acid synthesis
- Gluconeogenesis
Deficiency:
- Rare
- Hair loss, skin rash
- Can occur from eating raw egg whites (avidin binds biotin)
Vitamin B₉ (Folic Acid/Folate)
Sources:
- Green leafy vegetables (name from Latin “folium” = leaf)
- Legumes, liver
- Fortified grains
Functions:
- Coenzyme in one-carbon transfers
- DNA synthesis (important for cell division)
- RBC formation
- Crucial in pregnancy (neural tube development)
Deficiency:
- Megaloblastic anemia (large, immature RBCs)
- Neural tube defects in fetus (spina bifida)
- Pregnant women need supplements
Vitamin B₁₂ (Cobalamin)
Sources:
- Animal products only: Meat, fish, eggs, dairy
- Not found in plants (vegans need supplements)
- Contains cobalt (only vitamin with metal)
Functions:
- Coenzyme in methyl transfers
- DNA synthesis
- Myelin sheath formation (nerve protection)
- RBC maturation
Deficiency:
- Pernicious anemia (large, immature RBCs)
- Nerve damage (demyelination)
- Fatigue, weakness
- Irreversible nerve damage if prolonged
Unique: Requires intrinsic factor (from stomach) for absorption
Vitamin B₁₂ is unique because:
1. Only animal sources:
- Meat, fish, eggs, dairy
- No plant foods contain B₁₂
- Plants don’t need or make B₁₂
2. Bacterial origin:
- Made by bacteria
- Animals accumulate from bacteria in gut/diet
- Plants don’t accumulate it
3. Essential functions:
- DNA synthesis
- Nerve function
- RBC formation
4. Deficiency in vegans:
- Without animal products → no B₁₂
- Takes years to deplete stores
- Eventually: anemia, nerve damage
Solution for vegans:
- B₁₂ supplements (essential!)
- Fortified foods (plant milks, cereals)
- Nutritional yeast (fortified)
JEE Tip: B₁₂ = only vitamin exclusively from animal sources!
Vitamin C (Ascorbic Acid)
Chemical name: L-Ascorbic acid
Sources:
- Citrus fruits (oranges, lemons, limes)
- Strawberries, kiwi
- Tomatoes, peppers
- Broccoli, cabbage
Functions:
- Antioxidant: Scavenges free radicals
- Collagen synthesis: Hydroxylation of proline and lysine
- Iron absorption: Enhances Fe²⁺ absorption
- Immune function: Supports white blood cells
Deficiency:
- Scurvy:
- Bleeding gums, loose teeth
- Poor wound healing
- Skin hemorrhages
- Weakness, anemia
- Sailors’ disease (cured by citrus fruits)
Properties:
- Strong reducing agent
- Destroyed by heat and oxidation
- Need fresh fruits/vegetables
Comparison Table
| Vitamin | Chemical Name | Type | Main Function | Deficiency Disease |
|---|---|---|---|---|
| A | Retinol | Fat | Vision, skin | Night blindness, Xerophthalmia |
| D | Calciferol | Fat | Ca absorption | Rickets, Osteomalacia |
| E | Tocopherol | Fat | Antioxidant | Rare (hemolytic anemia) |
| K | Phylloquinone | Fat | Blood clotting | Hemorrhage |
| B₁ | Thiamine | Water | Carb metabolism | Beriberi |
| B₂ | Riboflavin | Water | FAD coenzyme | Ariboflavinosis |
| B₃ | Niacin | Water | NAD coenzyme | Pellagra |
| B₆ | Pyridoxine | Water | Amino acid metabolism | Anemia, dermatitis |
| B₉ | Folic acid | Water | DNA synthesis | Megaloblastic anemia |
| B₁₂ | Cobalamin | Water | DNA, nerves | Pernicious anemia |
| C | Ascorbic acid | Water | Collagen, antioxidant | Scurvy |
Common Mistakes to Avoid
Wrong: “All vitamins need daily consumption”
Correct:
- Water-soluble (B, C): Need daily intake (not stored)
- Fat-soluble (A, D, E, K): Stored in body, don’t need daily
JEE Tip: Storage determines frequency of intake!
Wrong: “Vitamins are natural, so safe in any amount”
Correct:
Fat-soluble: Can accumulate → toxic in excess
- Vitamin A: Liver damage, birth defects
- Vitamin D: Hypercalcemia, kidney stones
Water-soluble: Excess excreted, generally safe
JEE Fact: Fat-soluble vitamins can be toxic!
Wrong: Mixing up deficiency diseases
Correct - Remember pairs:
- Vitamin A → Night blindness (A for eyes)
- Vitamin D → Rickets (D for Deformed bones)
- Vitamin K → Hemorrhage (K for Koagulation)
- Vitamin C → Scurvy (C for Citrus cure)
- Vitamin B₁ → Beriberi (B₁ sounds like Beri-Beri)
JEE Strategy: Associate each vitamin with ONE key disease!
Practice Problems
Level 1: Foundation (NCERT)
Q: Classify the following vitamins as fat-soluble or water-soluble: A, B₁, C, D, E, K, B₁₂
Solution:
Fat-soluble:
- Vitamin A (Retinol)
- Vitamin D (Calciferol)
- Vitamin E (Tocopherol)
- Vitamin K (Phylloquinone)
Mnemonic: ADEK
Water-soluble:
- Vitamin B₁ (Thiamine)
- Vitamin B₁₂ (Cobalamin)
- Vitamin C (Ascorbic acid)
- All B-complex vitamins
Mnemonic: B and C
Q: Match the vitamin with its deficiency disease: (a) Vitamin A (b) Vitamin C (c) Vitamin D (d) Vitamin B₁
Solution:
(a) Vitamin A → Night blindness, Xerophthalmia
- Loss of vision in dim light
- Dry eyes
(b) Vitamin C → Scurvy
- Bleeding gums
- Poor wound healing
(c) Vitamin D → Rickets (children), Osteomalacia (adults)
- Soft, deformed bones
- Poor calcium absorption
(d) Vitamin B₁ → Beriberi
- Heart failure (wet)
- Nerve damage (dry)
Level 2: JEE Main
Q: Why is Vitamin D called the “sunshine vitamin”? What is its function?
Solution:
Why “sunshine vitamin”?
Synthesis in skin:
- UV radiation (from sunlight) converts 7-dehydrocholesterol in skin
- Converted to Vitamin D₃ (cholecalciferol)
- Body can make its own Vitamin D with sun exposure
- Only vitamin that can be synthesized by body
Recommended: 10-30 minutes of sun exposure daily
Function:
Primary: Calcium and phosphorus homeostasis
Mechanisms:
- Increases Ca²⁺ absorption from intestine
- Promotes bone mineralization
- Helps deposit Ca and P in bones
- Maintains blood Ca²⁺ levels
Result:
- Strong bones and teeth
- Prevents bone disorders
Deficiency:
- Children: Rickets (soft, bent bones)
- Adults: Osteomalacia (bone pain, weakness)
- Elderly: Osteoporosis (brittle bones)
JEE Fact: Indoor lifestyles and pollution reduce Vitamin D synthesis!
Q: Why don’t water-soluble vitamins cause toxicity even in large doses, while fat-soluble vitamins can?
Solution:
Water-soluble vitamins (B, C):
1. Not stored:
- Dissolved in blood and body fluids
- Excreted in urine daily
- Cannot accumulate
2. Excess eliminated:
- Kidneys filter excess
- Removed quickly
- No buildup
3. Result:
- No toxicity (excess just wasted)
- Need regular intake
Fat-soluble vitamins (A, D, E, K):
1. Stored in body:
- Dissolve in fats and oils
- Stored in liver and adipose tissue
- Accumulate over time
2. Slow excretion:
- Not easily eliminated
- Remain in body for months
3. Result:
- Can reach toxic levels
- Especially A and D
- Cause hypervitaminosis
Examples of toxicity:
- Vitamin A: Liver damage, birth defects, bone pain
- Vitamin D: Hypercalcemia, kidney stones, calcification
Conclusion:
- Solubility determines storage
- Storage determines toxicity risk
- Water-soluble = safe, Fat-soluble = can be toxic
JEE Principle: “What dissolves in water, flows out; what dissolves in fat, stays put!”
Level 3: JEE Advanced
Q: Explain why Vitamin C deficiency causes scurvy (bleeding gums, poor wound healing).
Solution:
Biochemical role of Vitamin C:
Vitamin C (ascorbic acid) is essential for collagen synthesis:
Step 1: Collagen formation
- Collagen = major protein in connective tissue
- Provides strength to skin, gums, blood vessels, bones
Step 2: Hydroxylation reactions
- Vitamin C is cofactor for enzymes:
- Prolyl hydroxylase
- Lysyl hydroxylase
Step 3: These enzymes hydroxylate:
- Proline → Hydroxyproline
- Lysine → Hydroxylysine
Step 4: Hydroxyproline and hydroxylysine:
- Form H-bonds in collagen triple helix
- Stabilize collagen structure
- Give strength to tissues
Without Vitamin C:
No hydroxylation occurs:
- Proline and lysine not modified
- Collagen structure unstable
- Cannot form proper triple helix
- Defective collagen
Consequences (Scurvy):
1. Bleeding gums:
- Weak collagen in gum tissue
- Blood vessels fragile
- Easy bleeding
2. Poor wound healing:
- Cannot make strong collagen
- Wounds don’t close properly
- Scars don’t form
3. Skin hemorrhages:
- Weak blood vessel walls
- Capillaries rupture
- Bruising, bleeding under skin
4. Loose teeth:
- Weak connective tissue in gums
- Teeth not held firmly
Summary:
$$\text{Vitamin C} \rightarrow \text{Hydroxylation} \rightarrow \text{Strong collagen} \rightarrow \text{Healthy tissues}$$Without Vitamin C:
$$\text{No hydroxylation} \rightarrow \text{Weak collagen} \rightarrow \text{Scurvy symptoms}$$JEE Insight: This shows how a small molecule (vitamin) is essential for major structural protein (collagen)!
Quick Revision Box
Fat-Soluble (ADEK):
| Vitamin | Function | Deficiency |
|---|---|---|
| A | Vision | Night blindness |
| D | Ca absorption | Rickets |
| E | Antioxidant | Rare |
| K | Blood clotting | Hemorrhage |
Water-Soluble (B-Complex + C):
| Vitamin | Function | Deficiency |
|---|---|---|
| B₁ | Carb metabolism | Beriberi |
| B₂ | FAD coenzyme | Cheilosis |
| B₃ | NAD coenzyme | Pellagra |
| B₉ | DNA synthesis | Megaloblastic anemia |
| B₁₂ | DNA, nerves | Pernicious anemia |
| C | Collagen synthesis | Scurvy |
Teacher’s Summary
1. Classification by Solubility:
Fat-soluble: A, D, E, K (ADEK)
- Stored in body
- Can be toxic in excess
- Don’t need daily intake
Water-soluble: B-complex, C
- Not stored (excreted)
- No toxicity
- Need regular intake
2. Important Diseases (HIGH-YIELD):
- Vitamin A → Night blindness
- Vitamin D → Rickets, Osteomalacia
- Vitamin K → Hemorrhage
- Vitamin B₁ → Beriberi
- Vitamin B₉ → Megaloblastic anemia
- Vitamin B₁₂ → Pernicious anemia
- Vitamin C → Scurvy
3. Unique Features:
- Vitamin D: Can be synthesized (sunshine)
- Vitamin K: Made by gut bacteria
- Vitamin B₁₂: Only from animal sources
- Vitamin C: Destroyed by heat
4. JEE Focus:
- Solubility classification
- Major deficiency diseases
- Sources (especially B₁₂ from animals only)
- Why toxicity in fat-soluble only
“Vitamins may be micro, but their impact is macro!”
Next: Study Enzymes to learn about biological catalysts and enzyme mechanisms!