Vitamin D is a steroid pro hormone. It is represented by steroids that occur in animals, plants and yeast. By various metabolic changes in the body they give rise to a hormone known as calcitriol, which plays central role in calcium and phosphate metabolism. Ergosterol occurs in plants and 7-dehydrocholesterol in animals. Ergosterol differ from 7-dehydrocholesterol only in its side chain, which is unsaturated and contain an extra methyl group. Ultraviolet irradiation cleaves the B ring of both compounds. Ergocalciferol (vitamin D2) may be made commercially from plants in this way whereas in animals cholecalciferol (Vitamin D3) is formed from 7-dehydrocholesterol a precursor in cholesterol bio synthesis) in exposed skin. Both Vitamins D2 and vitamin D3 are of equal potency.
Vitamin D2
Vitamin D2 is produced from ergosterol in the plants on exposure to the sunlight. In 1920 Vitamin D2 was produced commercially by exposure of the foods to ultraviolet rays. Ergosterol differ from 7-dehydrocholesterol only in its side chain, which is unsaturated and contain an extra methyl group. Ultraviolet irradiation cleaves the B ring of ergocalciferol.
Vitamin D3
Vitamin D3 is formed from 7-dehydrocholesterol by the action of sunlight and dietary vitamin D3 after absorption from miscelles in the intestine followed by transport in the lymphatics circulate in the blood bound to a specific globulin, Vitamin D- binding protein. Vitamin D3 is taken up by the liver, where it is hydroxylated at the 25th position by Vitamin D3- 25- hydroxylase, an enzyme of the endoplasmic reticulum.25- hydroxyvitamin D3 is the major form of vitamin in the circulation and storage form in the liver. The major function of the Vitamin D is to maintain the levels of calcium and phosphorous in the blood. It is essential to maintain strong and long bones. It has also been found to help prevent osteoporosis, hypertension, cancer and many other autoimmune diseases.
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Comparison: Vitamins D2 and vitamin D3 • Vitamin D2 is produced in plant whereas Vitamin D3 is produced in animals by exposure to sunlight. • Vitamin D2 is produced from ergosterol by action of sunlight whereas Vitamin D3 is formed from 7-dehydrocholesterol by the action of sunlight. • Vitamin D2 is produced in the food items by exposure to sunlight whereas Vitamin D3 is produced by exposure of the skin to the sunlight. • Ergosterol differ from 7-dehydrocholesterol only in its side chain, which is unsaturated and contain an extra methyl group • Vitamin D2 has a shorter shelf life when compared to Vitamin D3. This may be the reason for its efficacy to be lesser than that of Vitamin D3.
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Summary
Deficiency of vitamin can cause Rickets and Osteomalacia which is a kind of skeletal deformity. The people who are at risk of Vitamin D deficiency should take Vitamin D rich diet or take it as supplement as its deficiency can result in weak bones especially in older and obese population.