Cholecalciferol (English: Cholecalciferol, also known as vitamin D3 or cholecalciferol) is a kind of vitamin D. 7-dehydrocholesterol produced by dehydrogenation of cholesterol can form cholecalciferol by ultraviolet irradiation, so that is It is said that the vitamin D of cholecalciferol is 7-dehydrocholesterol. Cholecalciferol is hydrolyzed in the liver to form 25-hydroxycholecalciferol, which is then hydroxylated to 1,25-dihydroxycholecalciferol in the kidney. This substance is 50% more active than cholecalciferol. It has been proven to be a truly active form of vitamin D in the body. And 1,25-dihydroxycholecalciferol is a hormone secreted by the kidney, so in fact cholecalciferol is also a prohormone. At the same time, vitamin D is a fat-soluble vitamin, also seen as a hormone precursor acting on calcium and phosphorus metabolism. It is closely related to sunlight, so it is also called "sunshine vitamin".