The 25-hydroxyvitamin D test is to see if there is a lack of vitamin D in the body.

Vitamin D is a sterol derivative that has an anti-rickets effect and is also called an anti-rickets vitamin. It is currently believed that vitamin D is also a steroid hormone, and the most important members of the vitamin D family are VD2 (ergocalciferol) and VD3 (cholecalciferol). Vitamin D is a derivative of different provitamin D after ultraviolet irradiation.

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Vitamin D is a sterol derivative with resist Rickets effect, also known as anti-rickets vitamins. Plants do not contain vitamin D, but provitamin D exists in both animals and plants. Vitamin D is a fat-soluble vitamin with five compounds. The ones that are more closely related to health are vitamin D2 and vitamin D3.

They have the following three characteristics: it exists in some natural foods; the human body stores 7-dehydrocholesterol generated from cholesterol under the skin, which can be converted into vitamin D3 after being exposed to ultraviolet rays. Proper sunbathing is enough to meet the body's need for vitamin D.