The detection of VDR abundance throughout the immune system, the observation that VDR expression is regulated by immune signalling, and the detection of CYP27B1 expression by immune cells has directed vitamin D research into the area of immunology [77,78,79,80,81], with associations of low serum 25(OH)D3 levels seen with autoimmune diseases, cancer, cardiovascular disease and respiratory infections [82,83,84,85]. The gene discussed is VDR; the disease is respiratory tract infectious disorder.