CYP24A1 and vitamin D deficiency: Vitamin D deficiency could contribute to BPD development after endotoxin exposure through increased expression of CYP24A1, a vitamin D regulatory enzyme, and decreased expression of vitamin D receptors and 1α-OHase in the lung [20], and of VEGF expression and secretion, thereby impairing the processes of angiogenesis and vasculogenesis [74–76].