Figure 1
From: The role of vitamin D in pulmonary disease: COPD, asthma, infection, and cancer
Metabolism and effects of VitD. VitD can be obtained from food or from synthesis in the skin under exposure to light. The precursor is hydroxylated cytochrome P450 25-hydroxylase enzymes CYP27A1 and/or CYP2R1 and subsequently by the cytochrome P450 enzyme 25-hydroxyvitamin D-1α-hydroxylase (CYP27B1) and converted to the bioactive 1,25-(OH)2D3, which has role in Ca and bone metabolism and, in addition, in several other biological processes. Of note, bioactive 1,25-(OH)2D3 can also be generated in lung epithelia cells and monocytes/macrophages.