CYP2R1 and vitamin D deficiency: For example, in the fasting state, a significant reduction in the expression of CYP2R1 can be observed.(92) In a murine model of DM, a 50% reduction in mRNA and protein expression of CYP2R1 is demonstrable.(92) This study identified novel molecular mechanisms (involving PPAR γ coactivator a1 and estrogen‐related receptor) for vitamin D deficiency in DM and showed a novel negative feedback mechanism that controls cross‐talk between energy homeostasis and the vitamin D pathway.