Vitamins: Classification and Functions

Vitamins are essential organic compounds that our bodies require in small amounts for various metabolic processes. They don't provide energy themselves but are crucial for the proper functioning of enzymes and for maintaining overall health. A deficiency in any vitamin can lead to specific diseases. This comprehensive guide for JEE-level students covers the classification, sources, and key biological functions of vitamins.

1.0What are Vitamins?

Vitamins are a class of organic compounds that are vital for maintaining normal bodily functions, including growth, metabolism, and development. They are required in minute quantities and are generally not synthesized by the body in sufficient amounts, so they must be obtained from our diet. The term "vitamin" was coined from "vita" (life) and "amine," as early-discovered vitamins were thought to be amines.

Vitamins are classified by solubility. This property determines how they are absorbed, transported, and stored in the body, as well as their potential for toxicity.

2.0Classification of Vitamins

Vitamins are broadly classified into two main groups: fat-soluble and water-soluble.

Fat-Soluble Vitamins

These vitamins are stored in the body's fatty tissues and liver. They require bile acids for absorption in the intestines and can accumulate in the body over time, which means excessive intake can be toxic. There are four fat-soluble vitamins: A, D, E, and K.

1. Vitamin A (Retinol)

• Functions: Maintains vision (retinal pigment), supports immune system, promotes skin health.
• Sources: Carrots, spinach, liver, butter, fish oils.
• Deficiency: Night blindness, xerophthalmia, dry skin.

2. Vitamin D (Calciferol)

• Functions: Regulates calcium and phosphorus metabolism, essential for bone health.
• Sources: Sunlight (skin synthesis), milk, fish, egg yolk.
• Deficiency: Rickets (in children), osteomalacia (in adults).

3. Vitamin E (Tocopherol)

• Functions: Antioxidant, protects cell membranes, and prevents oxidative stress.
• Sources: Vegetable oils, nuts, green leafy vegetables.
• Deficiency: Muscle weakness, anaemia, and neurological problems.

4. Vitamin K

• Functions: Essential for blood clotting, synthesis of prothrombin.
• Sources: Green leafy vegetables, broccoli, soybean oil, intestinal bacteria.
• Deficiency: Prolonged bleeding, delayed clotting.

Water-Soluble Vitamins

These vitamins are not stored in the body in large amounts and must be consumed regularly. Excess is excreted through urine.

1. Vitamin B-Complex: The B-complex vitamins are a group of chemically distinct compounds that act as coenzymes in metabolism.

• Vitamin B1 (Thiamine)
• • Functions: Helps in carbohydrate metabolism, nerve conduction.
  • Sources: Whole grains, legumes, nuts, pork.
  • Deficiency: Beriberi, nerve damage.
• Vitamin B2 (Riboflavin)
• • Functions: Part of FAD/FMN coenzymes in oxidation-reduction reactions.
  • Sources: Milk, eggs, green vegetables.
  • Deficiency: Cracks at mouth corners, dermatitis, eye disorders.
• Vitamin B3 (Niacin)
• • Functions: Component of NAD/NADP, supports energy metabolism.
  • Sources: Meat, peanuts, whole grains.
  • Deficiency: Pellagra (symptoms: dermatitis, diarrhea, dementia).
• Vitamin B5 (Pantothenic Acid)
• • Functions: Component of Coenzyme A, essential in fatty acid metabolism.
  • Sources: Eggs, meat, whole grains, broccoli.
  • Deficiency: Rare, but may cause fatigue and cramps.
• Vitamin B6 (Pyridoxine)
• • Functions: Amino acid metabolism, neurotransmitter synthesis.
  • Sources: Bananas, poultry, fish, nuts.
  • Deficiency: Anemia, depression, irritability.
• Vitamin B7 (Biotin)
• • Functions: Coenzyme in carboxylation reactions, fat and protein metabolism.
  • Sources: Egg yolk, nuts, legumes.
  • Deficiency: Dermatitis, hair loss, fatigue.
• Vitamin B9 (Folic Acid)
• • Functions: DNA synthesis, cell division, red blood cell formation.
  • Sources: Leafy greens, legumes, fortified cereals.
  • Deficiency: Megaloblastic anemia, neural tube defects in newborns.
• Vitamin B12 (Cobalamin)
• • Functions: DNA synthesis, myelin formation, red blood cell production.
  • Sources: Meat, fish, dairy (not present in plants).
  • Deficiency: Pernicious anemia, neurological disorders.

2. Vitamin C (Ascorbic Acid)

• Functions: Antioxidant, collagen synthesis, enhances iron absorption, strengthens immunity.
• Sources: Citrus fruits, guava, tomatoes, green peppers.
• Deficiency: Scurvy (bleeding gums, poor wound healing, fatigue).

3.0Functions of Vitamins

Vitamins play a vital role in maintaining normal physiological functions of the human body. Although they are required only in small amounts, their absence or deficiency can cause severe health issues. The functions of vitamins are as follows:

Act as Coenzymes

• Many vitamins, especially B-complex vitamins, act as coenzymes in enzymatic reactions.
• Example: Vitamin B1 (Thiamine) helps in carbohydrate metabolism, while Vitamin B3 (Niacin) forms NAD⁺/NADP⁺, essential for energy production.

Maintain Healthy Vision and Skin

• Vitamin A is essential for normal vision and prevents night blindness.
• It also supports healthy skin and epithelial tissues.

Bone Growth and Development

• Vitamin D regulates calcium and phosphorus absorption, ensuring strong bones and teeth.
• Vitamin K aids in bone mineralization and blood clotting.

Antioxidant Protection

• Vitamins C and E act as antioxidants, protecting cells from free radical damage.
• This prevents premature aging and reduces risk of chronic diseases.

Formation of Blood and Nervous System Health

• Vitamin B12 and Folic Acid (B9) are essential for red blood cell formation and DNA synthesis.
• Vitamin B6 supports neurotransmitter synthesis, maintaining a healthy nervous system.

Boosting Immunity

• Vitamin C strengthens the immune system by enhancing white blood cell function.
• Vitamin A also plays a role in maintaining immune defense.

Wound Healing and Collagen Formation

• Vitamin C is necessary for collagen synthesis, aiding in tissue repair and wound healing.

Metabolism and Energy Production

• B-complex vitamins act as coenzymes in the metabolism of carbohydrates, fats, and proteins, helping in energy release from food.

4.0Sources of Vitamins

• Natural Sources: Fruits, vegetables, dairy, fish, eggs, grains, meat.
• Sunlight: Important source of Vitamin D.
• Intestinal Bacteria: Produce Vitamin K and some B vitamins.
• Fortified Foods: Cereals, milk, bread.

5.0Deficiency Diseases of Vitamins

• Vitamin A: Night blindness, xerophthalmia.
• Vitamin D: Rickets, osteomalacia.
• Vitamin E: Hemolytic anemia, muscle weakness.
• Vitamin K: Excessive bleeding.
• Vitamin B1: Beriberi.
• Vitamin B2: Cheilosis, photophobia.
• Vitamin B3: Pellagra.
• Vitamin B6: Anaemia, nervous disorders.
• Vitamin B9: Megaloblastic anaemia.
• Vitamin B12: Pernicious anaemia.
• Vitamin C: Scurvy.