维生素 D 是目前所知唯一能转变成激素形式的维生素。它是类固醇,其主要活性形式以一种与其它类固醇激素完全相同的方式起作用。如机体能得到充足的紫外线照射,则不需从饮食获取。不论是皮肤合成还是来自饮食的维生素 D_3,都必须成为具有活性的代谢产物才能发挥作用。第一个活化步骤主要在肝脏进行,维生素 D_3转化成25-OHD_3(25羟胆骨化醇)。 Vitamin D is by far the only vitamin that can be converted into a hormone form. It is a steroid whose main active form acts in exactly the same way as other steroid hormones. If the body can get enough ultraviolet radiation, you do not need to get from the diet. Whether it is skin synthesis or dietary vitamin D_3, must be an active metabolite to play a role. The first activation step is mainly in the liver, vitamin D_3 into 25-OHD_3 (25 hydroxycholecalciferol).