Figure 1. Epidemiological associations between vitamin D deficiency and lung diseases and proposed mechanisms.

Vitamin D deficiency appears to increase susceptibility to TB infections due to lack of induction of the cathelicidin antimicrobial peptide. Vitamin D deficient individuals also report more frequent respiratory tract infections perhaps due to less production of cathelicidin and/or increased production of chemokines leading to uncontrolled inflammatory response. Lastly vitamin D deficiency has been associated with higher prevalence of asthma and a more severe course of this disease. Two mechanisms have been proposed: i) Increased risk of respiratory viral infection. ii) Lack of vitamin D suppressive effects on adaptive immunity, in particular dendritic cells and T regulatory cells.