Vitamin d (vitamin
D
) is a sterol derivative with anti-rickets effect, also known as anti-rickets vitamin. At present, it is considered that vitamin D is also a steroid hormone, and the most important members of vitamin D family are VD2 (ergocalciferol) and VD3 (cholecalciferol). Vitamin D is a derivative of different provitamins after ultraviolet irradiation. Plants do not contain vitamin D, but both animals and plants contain provitamin.
Vitamin D is a fat-soluble vitamin with five compounds, among which vitamin D2 and vitamin D3 are closely related to health. They have the following three characteristics: they exist in some natural foods; 7- dehydrocholesterol produced by cholesterol is stored under the skin of human body and can be converted into vitamin D3 after ultraviolet irradiation. Proper sunbathing is enough to meet the human body's demand for vitamin D.