25-Hydroxy Vitamin D (25-OH-VD)

Vitamin D (VD) is an essential substance for human health, growth and development. Its deficiency or excess is closely related to many diseases, such as musculoskeletal diseases, respiratory system diseases, cardiovascular disease, immune diseases, kidney diseases, neuropsychiatric diseases, etc.

Vitamin D is a steroid hormone that maintains the body's calcium balance by regulating intestinal absorption and renal reabsorption. There are two main types of vitamin D: vitamin D2 (VD2) and vitamin D3 (VD3). VD2 is mainly obtained from ingested food (accounting for about 10% of the total VD), and VD3 is mainly generated when the skin is irradiating with ultraviolet rays of the sun light. Internal vitamin D is transported to the liver via the blood after combining with albumin and VD-binding protein. Under the participation of 25-hydroxylase secreted by the liver, the 25-position of VD is hydroxylated to 25-(OH)-VD. In kidney, 25-(OH)-VD is further converted into biologically active 1, 25-(OH)2-VD3 (1, 25-dihydroxyvitamin D3, also known as calcitriol) under the action of 1α-hydroxylase. Finally, under the load of DBP transport protein, it reaches target organs such as small intestine and bone through the blood and binds to muclear receptor (VDRn) or membrane receptor (VDRm) to exert corresponding biological effects.

25-(OH)-VD is the main storage form of vitamin D in the body, accounting for more than 95% of the total VD. Due to its long half-life (2 to 3 weeks), not affected by blood calcium or thyroid, Therefore, 25-(OH)-VD has been recognized as the best indicator to objectively evaluate the VD content in the body.

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