The role of vitamin D and daily requirements

It has anti-rickets effect and is rich in animal liver, milk and egg yolks, especially cod liver oil. There are two natural vitamin D, ergocalciferol D2 and cholecalciferol D3. Ergosterol 24-methyl-22dehydro-7-dehydrocholesterol contained in vegetable oil or yeast can be converted into vitamin D2 when activated by ultraviolet light. 7-dehydrocholesterol under the skin of animals can also be converted into vitamin D3 by ultraviolet irradiation, so ergosterol and 7-dehydrocholesterol are often called pro-vitamin D. In animals, vitamins D2 and D3 in food can be absorbed in the small intestine, absorbed into the blood through lymphatic vessels, mainly absorbed by the liver, and then stored in adipose tissue or other lipid-rich tissues. The main vitamin D in the human body is D3, which comes from the original vitamin D3-dehydrocholesterol. Therefore, getting more sun exposure is one of the main ways to prevent vitamin D deficiency. Vitamins D2 and D3 are colorless crystals that are relatively stable in nature and are not easily destroyed. Neither vitamin D2 nor D3 has biological activity in itself. They must undergo a series of metabolic transformations in animals before they can become active substances. This transformation is mainly a hydroxylation reaction in the liver and kidney. It is first hydroxylated to 25-hydroxyvitamin D3 in the liver, and then further hydroxylated to 1,25-OH2-D3 in the kidney, which is the active form of vitamin D3 in the body. 1,25-dihydroxyvitamin D3 has significant activity in regulating calcium and phosphorus metabolism Figure 11. It promotes the absorption and transport of phosphorus by the small intestine mucosa, and also promotes the reabsorption of calcium and phosphorus by the renal tubule. In bones, it not only helps calcify new bone, but also promotes the release of calcium from the old bone marrow, so that the bone can be continuously renewed, while maintaining the balance of blood calcium. Because 1,25-dihydroxyvitamin D3 is transferred to the blood circulation after being synthesized in the kidney and acts on long-distance target tissues such as the small intestine, renal tubule, and bone tissue, which basically conforms to the characteristics of hormones, some people classify vitamin D as hormone substances. Vitamin D regulates calcium, so it is necessary for the normal development of bones and teeth. Especially among pregnant women, infants and teenagers, there is a large need. If the amount of vitamin D is insufficient at this time, the calcium and phosphorus in the blood will be lower than normal, and bones will become soft and deformed: it occurs in children, called rickets; in pregnant women, it is osteomalacia. 1 gram of vitamin D is 40 million international units. The daily requirement for infants, teenagers, pregnant women and breast-feeding workers is 400 to 800 units.

Vitamin D was first extracted from cod liver oil by chemist Carl in 1926. It is a light yellow crystal with a melting point of 115~118 ° C. It is insoluble in water and can be soluble in organic solvents such as ether. It is chemically stable and can still maintain biological activity at 200 ° C, but is easily destroyed by ultraviolet light. Therefore, all medicines containing vitamin D should be stored in brown bottles. The physiological