Chemistry

ERGOSTEROL

IN PLANTS

IN ANIMALS

7-dehydro

cholesterol

cholecalciferol

25 –

dihydroxy

chole

calciferol

1,25

dihydroxy

chole

calciferol

sunlight

Calcidiol 2,5 hydroxylase

Calcidiol 1-hydroxylase

REGULATION OF SYNTHESIS

•Concentration of calcitriol is regulated by plasma levels of calcium & phosphate

• Low plasma phosphate increases activity of calcidiol 1-hydroxylase – DIRECT

• Low plasma calcium enhances parathyroid hormone production which in turn activates 1-hydroxylase - INDIRECT

RDA

Adults:400 IU in Western countries200 IU in IndiaChildren:400 IUPregnancy & Lactation:600 IU

Hypervitaminosis

•Among the Vitamins D is most toxic on overdose• Demineralization of bone• Increased Ca absorption- hypercalcemia• Deposition of ca in kidneys & arteries• Renal calculi• Loss of appetite• Nausea• Increased thirst• Loss of weight