Principles of Biochemistry

10.2.2 Vitamin D

10.2.2.Vitamin D (Calciferol)

Vitamin D refer to a group of compounds. It is generated from the provitamin, 7-dehydrocholesterol present in animals by the action of sunlight forming Cholecalciferol (Vitamin D₃). Ergosterol occuring in plants is the precursor of Ergocalciferol (Vitamin D₂). It differs from 7-dehydrocholesterol only in its side chain, which is unsaturated and contains an extra methyl group. Ultraviolet irradiation cleaves the B ring of both compounds and form respective D vitamin. Ergocalciferol (Vitamin D₂) may be made commercially from plants in this way . Both vitamins D₂ and D₃ are of equal potency.

Functions: Vitamin D is essential for bone health and may reduce cancer risk. In children it promotes bone development and growth. In adults it is needed for bone maintenance. It enhances absorption of calcium and phosphorus in the small intestine. It also control rate of calcification of bones. Vitamin D stimulates the transport of mRNA for calcium binding protein.

Deficiency

Deficiency of Vitamin D causes rickets. It occurs in young children. The bones weaken and the skeleton fails to harden. This condition is characterized by “bow legs”, Knock- knees, rachitic rosary and other skeletal deformities. Osteomalacia occurs in adults who are not exposed to sunlight or who do not receive adequate amounts of vitamin D in the diet. It is due to softening of bones resulting from lack of calcium and phosphate. It increases the risk for fractures in the hips, spine and other bones. Along with osteomalacia, vitamin D deficiency is associated with osteoporosis, increased bone turnover and an increased risk of bone fracture.

RDA

Infants :400IU

Children :400IU

Adults :200IU

Pregnant women :400IU

Lactating women :400IU

1 IU= 0.025micro g of cholecalciferol

Sources

Good sources : Oily fish, egg yolk, and liver

Fair sources : Milk,

An individual’s exposure to sunlight, which is governed by latitude, season, and other factors, influences the relative dependence on dietary sources to meet vitamin D requirements.

Hypervitaminosis: Extremely large amounts of vitaminD intake cause hypervitaminosis. The early symptoms are anorexia, thirst, constipation and polyurea, followed later by nausea, vomiting and diarrhea. Increased urinary excretion of calcium and phosphate may lead to urinary lithiasis and the hypercalcemia. The kidney, arteries, muscles and gastric mucosa are mainly involved.