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Vitamin D

Vitamin D. Vitamin D. Vitamin D occurs in two forms, as “Vitamin D 2 ” (ergocalciferol), chief Vit D precursor in plants is, ergostreol.

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Vitamin D

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  1. Vitamin D

  2. Vitamin D Vitamin D occurs in two forms, as • “Vitamin D2” (ergocalciferol), chief Vit D precursor in plants is, ergostreol. 2 “Vitamin D3” (cholecalciferol) the main form occurring in animal cells and developing in skin on exposure to ultraviolet light from 7- dehydrocholesterol

  3. Absorption • Vit D is stable through storage, processing and cooking and is absorbed effectively from GIT • Any abnormality in fat mal-absorption may cause malabsorption of Vit D

  4. Animal sources of Vit D • Eggs • Liver • Butter • Fish

  5. Absorption and metabolism Vitamin D3 is obtained from two sources: • Vit D3 is obtained from diet or food supplements. • From the conversion of 7-dehydro cholesterol in the skin by ultraviolet light to pre Vit- D3 which then slowly equilibrates to Vit- D3

  6. Absorption and metabolism Before it can function, Vit D3 must be activated by hydroxylation which takes place both in liver & kidney. The initial conversion in the liver results in 25-hydroxy cholecalciferol (calcidiol), the major circulating form of Vit D3.

  7. Absorption and metabolism • 2nd hydroxylation takes place in the proximal tubule of the kidney, giving rise to 1,25-dihydroxycholecalciferol or calcitriol. • This form is then transported to bones, kidneys and intestines.

  8. Conversion of Vitamin D to the active form Cholesterol from diet Sunlight converts 7-dehydrocholesterol to previtamin D3 The liver converts previtamin D to 25-hydroxyvitamin D which appears in circulation. Cholecalciferol (Previtamin D3) 7 dehydrocholesterol in the skin The kidneys and other tissues convert it to an active form of 1,25-dihydroxyvitamin D 25-hydroxyvitamin D (circulating form) 1,25-dihydroxyvitamin D (active form)

  9. Sun exposure • Solar ultraviolet radiation (UV radiation) • Beneficial • Harmful • Skin cancer • Vitamin D obtained by UV- induced photosynthesis in the skin.  • Sunscreens and sun blocks • completely blocks photosynthesis of vitamin D

  10. Factors affecting Vit D synthesis The amount of Vit D formed by the action of sunlight on the skin is dependent on • Intensity of light • Length of exposure • Skin pigmentation

  11. Daily requirement • 400 iu (10ug) of Vit D per day promote optimal calcium absorption and enhance growth • Higher level is recommended for infants and children

  12. Daily requirement • With slowing and finally cessation of skeletal growth the daily Vit D allowance decreases to 300 i.u. (7.5 µg) for ages 19 through 22, & 200 i.u. (5 µg) for the later years. • During pregnancy and lactation the Vit D requirement is increased by 200 i.u. (5 µg) to allow for transfer across placenta and into breast milk

  13. Recommended Dietary Allowances Infants 0 – 0.5 10 g 0.5 – 1.0 10 g Children 1 – 3 10 g 4 – 6 10 g 7 – 10 10 g

  14. Recommended Dietary Allowances AdultsMale Female 11 – 14 10 10 15 – 18 10 10 19 – 22 7.5 7.5 23 – 50 5 5 51+ 5 5 Pregnancy + 5 Lactation + 5

  15. Functions It is a steroid and functions like other steroid hormones. It is not dietary essential when there is adequate exposure to ultraviolet light • Vit D plays a major role in the regulation of calcium and phosphate metabolism by promoting their intestinal absorption, influencing the process of bone mineralization.

  16. Functions • Vit D exerts its anti ricket action by making the intestinal mucosa permeable to calcium and phosphorus and facilitating the active transport of calcium across cell membranes.

  17. Effects of deficiency • A deficiency of Vit D causes impaired intestinal absorption of calcium and phosphorus and faulty mineralization of teeth and bones. • Skeletal malformation result from the inability of the softened bone to withstand weight bearing . In children this bone condition is termed rickets.

  18. Effects of deficiency Other symptoms of rickets include • Delayed closure of the fontanelles (suture lines in the skull) especially in premature infants • Projection of sternum (pigeon breast). • Spinal curvature. • Bowing of the legs and • Enlargement o the costochondral junction.

  19. Effects of deficiency • In adults this bone condition is termed as osteomalacia and is caused purely by lack of Vit D and calcium. • Particularly prevalent among pregnant and lactating oriental women.

  20. Effects of deficiency • Vit D is involved in neuromuscular activity and its deficiency cause tetany characterized by convulsions, muscle twitching and sharp flexion of the wrest and ankle joint. • This condition may also result from parathyroid disease or from insufficient dietary intake or intestinal absorption of calcium or Vit D • Dental caries are more prevalent among children with poor intakes of Vit D, calcium and phosphorus.

  21. Toxic Effects • Precisely not known • Toxicity symptoms include • Polyurea • Nocturia • Weight loss • Diarrhea & • Nausea

  22. Toxic Effects • Severe toxicity results in • Calcification of soft tissues such as • Blood vessels • Heart • Stomach • Bronchi & • Kidney

  23. Vitamin D and chronic diseases 1,25-dihydroxyvitamin D plays an important role in: • Regulating calcium and phosphate metabolism for bone health, • Autoimmune diseases, • Atopic dermatitis, • Cardiovascular disease, • Chronic respiratory diseases • Crohn’s disease and Inflammatory bowel disease, • Diabetes, type 1 and type 2 • Kidney disease, • Osteoarthritis, • Periodontal disease, • Rheumatoid arthritis, • Skin disorders, • Some cancers, • Infectious disease, • Schizophrenia

  24. THANKS

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