由于维生素 D 有促进小肠钙的吸收以及从骨组织动员骨盐的作用,以前认为它是维持血浆钙浓度恒定的钙调节因子。为了发挥此作用,维生素 D_3(以下简称 D_3)首先在肝中发生25位羟化,然后在肾脏发生1α位羟化,转化为最终活性物质1α,25-二羟基维生素D_3[1α,25(OH)_2D_3]。在靶组织小肠及骨骼 Vitamin D was previously thought to be a calcium regulator that maintains a constant plasma calcium concentration because of its role in promoting intestinal calcium absorption and bone mineral mobilization from bone tissue. In order to exert this effect, vitamin D_3 (hereinafter referred to as D_3) is first hydroxylated at 25 in the liver and then hydroxylated at the 1α position in the kidney to be converted into the final active substance 1α, 25-dihydroxyvitamin D_3 [1α, 25 (OH ) _2D_3]. In the target tissue small intestine and bone