[Update on recent progress in vitamin D research. Vitamin D Metabolism and Its Regulation.]

Vitamin D is taken up from food as D2 and D3 . Vitamin D3 is also synthesized from 7-dehydrocholesterol in the skin by the exposure of ultraviolet B. The D2 and D3 , which are called native vitamin D, are hydroxylated at C25 in the liver by CYP2R1 and then at C1 in the kidney by CYP27B1, to be converted to an active vitamin D metabolite, 1,25-dihydroxyvitamin D[1,25(OH)2 D]. CYP24A1 converts 25-hydroxyvitamin D(25OHD)and 1,25(OH)2 D to 24,25-dihydroxyvitamin D[24,25(OH)2 D]and 1,24,25-trihydroxyvitamin D[1,24,25(OH)3 D], respectively, to decrease the level of 1,25(OH)2 D. CYP27B1 and CYP24A1 are mainly expressed in the kidney but also detected in other tissues, and it is suggested that 1,25(OH)2 D produced in the extra-renal tissues may exert its effects locally.