The actions of 1,25(OH)2D are mediated through ligation with a nuclear vitamin D receptor (VDR), leading to the regulation of the transcription of over 1000 target genes. VDR is widely distributed in many different cells and tissues, including the immune system. VDR gene polymorphisms, located on chromosome 12q13.1, have been associated with higher prevalence of respiratory infections [74,75,76,77]. One of the main roles of vitamin D is to maintain calcium homeostasis by promoting calcium absorption in the intestine and reabsorption in the kidneys and stimulating bone remodeling by increasing osteoclasts number. This effect was the first to be discovered, studying the causes of rickets and osteomalacia, but now it is thought that vitamin D has physiological effects much broader that its role in mineral homeostasis and bone function [78], including regulation of immunity, fetal development [79], and pulmonary function [80]. In addition, vitamin D can also induce cathelicidin in gastrointestinal epithelium [81] and plays a role in controlling gastrointestinal infections [82].