Vitamin d metabolism

vitamin D metabolism

1. VITAMIN D METABOLISM

2. It is a fat soluble vitamin. Resembles sterols in structure and functions like a hormone. Synthesized by the body after exposure to UV rays or obtained from food sources VITAMIN D

3. SOURCES Fortified foods Milk, cheese, yogurt, orange juice Ready to eat cereals Sun exposure Rays from the sun trigger synthesis in the skin

4. Ergocalciferol (vitamin D2) is formed from ergosterol and present in plants. Cholecalciferol (vitamin D3) is found in animals. Ergocalciferol and cholecalciferol are sources for vitamin D activity and are referred as provitamins . CHEMISTRY

5. Both ergocalciferol and cholecalciferol are similar in structure expect that ergocalciferol has an additional methyl group and double bond. 25 hydroxy vit D3 ( calcidiol ) 1,25 dihydroxy vit D3 ( calcitriol ).

6. Absorption, Distribution, Metabolism Absorption Vitamin D is absorbed from the small intestine for which bile is essential. Distribution Stored in adipose tissue Metabolism Transported to the liver, then kidneys, where it is activated

7. Excretion Excreted in bile Metabolized to water soluble metabolites and then excreted in urine as well.

8. Calcitriol is biologically active form of vitaminD . It regulates the plasma levels of calcium and phosphate. It acts at 3 different levels: Action of calcitriol on intestine. Action of calcitriol on bone. Action of calcitriol on kidney. BIOCHEMICAL FUNCTIONS

9. It is an another metabolite of vitamin D. Synthesized in kidney by 24 hydroxylase . Exact function is not known. It is believed that when calcitriol concentration is adequate 24 hydroxylase leading to formation of less imp compound 24,25 DHCC. In this way to maintain homeostasis of calcium synthesis of 24,25 DHCC is also important. 24,25 dihydroxycholecalciferol .

10. Functions Cell differentiation inhibits proliferation and stimulates the normal differentiation of cells Immunity The inactive form of vitamin D aids in the formation of active vitamin D which enhances immunity and inhibits the development of autoimmune disease.

11. Functions Calcium balance With decreased dietary calcium, PTH is secreted and causes increased production of calcitriol , a hormone Calcitriol restores normal calcium levels by increased absorption of dietary calcium, increased mobilization of calcium from bone, and increased reabsorption from kidneys

12. Functions Heart disease Renin , important in regulation of blood pressure and heart health, is associated with vitamin D levels Maintaining normal phosphorus levels Bone cannot be properly mineralized without phosphorus

13. Deficiency During vitamin D deficiency, calcium absorption cannot be increased to meet body's needs Therefore, calcium is taken from bones to maintain normal serum levels

14. Risk Factors Higher melanin content (darker skin) Breast-fed infants Elderly Body covering/use of sunscreen Fat malabsorption syndrome Obesity Inadequate dietary intake Increased excretion Genetic susceptibility

15. Rickets Infantile tetany Poor growth Osteomalacia . DEFICIENCY

16. Diseases Rickets/Osteomalacia caused by lack of vitamin D, calcium, or phosphate, which leads to softening and weakening of the bones

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