Vitamins and Their Functions

Vitamins

• Vitamins are small organic molecules required in small quantities for various biochemical functions.
• They are essential cofactors for enzymatic reactions and cannot be synthesized by mammalian cells.
• Deficiency in vitamins produces characteristic diseases.

Classification of Vitamins

• Vitamins are divided into two types based on solubility:
  • Fat-soluble vitamins: A, D, E, and K.
  • Water-soluble vitamins: C and B complex.

Vitamin A

• Exists in three biologically active forms: retinol, retinal, and retinoic acid.
• Sources: animal sources like liver, egg yolk, and milk; carotenoids are provitamin A.
• Functions:
  • Maintenance of epithelium and mucous membranes.
  • Antioxidant activity.
  • Formation of healthy connective tissues, bones, and teeth.
  • Gene control and regulation of cell growth and differentiation.
  • Vision: forms rhodopsin pigments responsible for vision in dim light.
• Deficiency: leads to night blindness, hyperkeratinization, and increased risk of cancer.

Vitamin D

• Biologically active form: calcitriol.
• Sources: liver, egg yolk, and cod liver oil; 7-dehydrocholesterol is converted into vitamin D3 by UV irradiation.
• Functions:
  • Regulates calcium and phosphorus homeostasis.
  • Increases calcium absorption and reabsorption in the intestine and kidney.
  • Deposition of calcium and phosphate in bone (mineralization).
• Deficiency: leads to rickets in children and osteomalacia in adults.

Vitamin E

• Function: natural antioxidant preventing peroxidation of polyunsaturated membrane fatty acids.

Vitamin K

• Function: activates blood clotting proteins, factors II, VII, IX, and X.
• Deficiency: leads to defective blood clotting and hemorrhage.

Vitamin C

• Functions:
  • Potent antioxidant.
  • Absorption of iron by maintaining it in the ferrous state.
  • Cofactor for hydroxylation of proline and lysine residues in collagen.
  • Tyrosine metabolism and synthesis of epinephrine from tyrosine.
  • Synthesis of bile acids and steroidogenesis.
• Deficiency: leads to scurvy, characterized by capillary fragility, soft swollen gums, and decreased wound healing.

Vitamin B Complex

Vitamin B1 (Thiamine)

• Function: thiamine pyrophosphate (TPP) acts as a coenzyme in oxidative decarboxylation reactions in carbohydrate metabolism.
• Deficiency: leads to Beri Beri, characterized by GIT, neurological, and cardiovascular manifestations.

Vitamin B2 (Riboflavin)

• Function: flavin mononucleotide (FMN) and flavin adenine dinonucleotide (FAD) act as hydrogen carriers.

Vitamin B3 (Niacin or Nicotinic acid)

• Function: nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP) act as hydrogen carriers.
• Deficiency: leads to Pellagra, characterized by diarrhea, dermatitis, and dementia.

Vitamin B5 (Pantothenic Acid)

• Function: required for synthesis of coenzyme A, necessary for metabolism of carbohydrates, fats, and proteins.

Vitamin B6

• Function: pyridoxal phosphate (PLP) is a coenzyme for transamination reactions, required for synthesis and catabolism of amino acids, decarboxylation of amino acids, and in heme synthesis.

Folic Acid

• Function: tetrahydrofolic acid (FH4) acts as a coenzyme in protein metabolism and promotes red blood cell formation.
• Deficiency: leads to Megaloblastic anemia.