Furthermore, it is tempting to speculate that by the unique expression of CYP24A1 in the vascular endothelium, systemic vitamin D supplementation may have failed in the general COPD population [35–37], as 25(OH)D and 1.25(OH)2D are potentially inactivated prior to their translocation to airways and tissue residing immune cells [38]. This evidence concerns the gene CYP24A1 and chronic obstructive pulmonary disease.