Vitamin D is usually available in two forms, namely cholecalciferol (D3) and ergocalciferol (D2). Vitamin D is no longer a vitamin. Vitamin D3 is considered a prohormone. Vitamin D itself is not biologically active, and these important effects in the body are achieved by being metabolized into progeny products. Vitamin D is metabolized to 25-OH-D3 in the liver and then converted to 1α,25(OH)2D3 and 24R,25(OH)2D3 in the kidney to be biologically active.
Vitamin D maintains blood calcium and phosphorus stability, and 1,25(OH)2D3 binds to PTH to maintain blood calcium and phosphorus levels, including promoting calcium absorption and maintaining proper bone density. The beginning of the physiological cycle is the recognition of calcium by the parathyroid calcium receptor. When the blood calcium concentration drops, the parathyroid glands secrete PTH, which stimulates the kidney 25-OH-D-12-oxidase to convert more 1,25(OH)2D3 from the 25-OH-D3 storage pool. As the level of PTH increases, the synthesis of 1,25(OH)2D3 increases, resulting in increased calcium transport in the intestine, bone and kidney, which restores blood calcium to normal levels. This process is recognized by the calcium receptors of the parathyroid glands. Decreased PTH secretion is not only regulated by feedback of calcium activity, but also by the short feedback loop associated with 1,25(OH)2D3 to directly inhibit PTH secretion by the parathyroid glands.
Vitamin D is involved in the regulation of transcription of certain proteins; biotin D is involved in the transcription of calcium transporters and bone matrix proteins and the regulation of cell-cyclin transcription, including regulation of the transcription of calcium transporters and bone matrix proteins encoded by vitamin D-dependent genes, It also affects the transcription of cell-cyclin, reduces the proliferation of cells, and increases the differentiation of specific cells in the body (such as osteoclast precursors, intestinal cells, keratinocytes, etc.). This property of vitamin D can explain its role in bone resorption, calcium transport in the intestine, and in the skin.
Vitamin D can play a hormone-like role and participate in immune regulation in the body; in recent years, 1,25(OH)2D3 receptors such as brain, various bone marrow-derived cells, skin, thyroid, etc. have been found in many non-target tissues. , a view on the induction and differentiation of macrophages induced by 1,25(OH)2D3. 1,25(OH)2D3 also inhibited the production of interleukin II in activated T-lymphocytes, suggesting that this hormonal effect of vitamin D may be involved in immune regulation in vivo. This role has been successfully used to treat psoriasis and other skin diseases.
The role of vitamin D in reducing the risk of cancer; 1α,25(OH)2D3 plays an important role in many differentiated and value-added tissues and cells, including hematopoietic systems, keratinocytes, and cells that secrete parathyroid hormone and insulin. Many types of cancer cells, including breast and prostate cancer cells, are also target cells for the action of 1α,25(OH)2D3. In recent years, 1α,25(OH)2D3 analogs have been used to treat a variety of cancers.
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