Figure 2. The metabolism of vitamin D. The liver converts vitamin D to 25OHD. The kidney converts 25OHD to 1,25(OH)2D and 24,25(OH)2D. Other tissues contain these enzymes, but the liver is the main source for 25-hydroxylation, and the kidney is the main source for 1-hydroxylation. Control of metabolism of vitamin D to its active metabolite, 1,25(OH)2D, is exerted primarily at the renal level where calcium, phosphorus, parathyroid hormone, FGF23, and 1,25(OH)2D regulate the levels of 1,25(OH)2D produced.