The skin of human body can synthesize vitamin D which is needed by human body by sunlight (mainly ultraviolet rays). Vitamin D is an essential fat soluble vitamin for human beings. Pure vitamin D is a kind of white crystal, soluble in fat and lipid solvent. Its physical and chemical properties are stable. General cooking will not cause the loss of vitamin D, but it can cause damage when fat is rancid.
There are at least five forms of vitamin D, the most significant being cholecalciferol (vitamin D3) and ergosterol (vitamin D2). Is it amazing that vitamin D3 can be synthesized from a substance in our skin by ultraviolet irradiation in the sun?
Vitamin D is involved in the regulation of intracellular and extracellular calcium concentration and calcium and phosphorus metabolism; in addition, it also acts on many other organs and participates in the regulation of cell metabolism and differentiation. The main functions are as follows:
1. Maintain the stability of blood calcium and phosphorus. When the level of blood calcium decreased, it promoted the reabsorption of calcium in human body, and when the level of blood calcium increased, it increased the excretion of calcium and phosphorus through urine.
2. Promote the mineralization of bone, cartilage and teeth. Vitamin D can increase the absorption and utilization of calcium and phosphorus by different ways, promote the mineralization of bone cartilage and teeth, and constantly update to maintain normal growth, and prevent rickets in children and osteomalacia in adults.
3.Promote the absorption of calcium in the small intestine. The mechanism of calcium binding protein in promoting calcium absorption in small intestine needs further study.
4.Regulate gene transcription and immune function.
