The role of vitamin D in chronic obstructive pulmonary disease, asthma and other respiratory diseases.

There has been growing interest in recent years in the extraosseous effects of vitamin D. In this article, we review the physiology of vitamin D, the physiopathological effects associated with vitamin D deficit and the available evidence on its etiopathogenic role in respiratory diseases. Given the pleiotropic actions of vitamin D, it is biologically plausible that the deficit of this vitamin could play a pathogenic role of in the development of various respiratory diseases. However, the many epidemiological studies that have shown an association between low vitamin D levels and a higher risk of developing various respiratory diseases or a poorer prognosis if they do appear, were unable to show causality. Post-hoc analyses of some clinical trials, particularly in chronic obstructive pulmonary disease (COPD) and asthma, appear to suggest that some patient subtypes may benefit from correction of a vitamin D deficit. In this respect, it would be interesting to determine if the interindividual differences found in the effect of vitamin D deficit and responses to correcting this deficit could be explained by the genetic variants involved in vitamin D metabolism. Ultimately, only appropriately designed clinical trials will determine whether 25-OHD supplements can prevent or improve the course of the various respiratory diseases in which an epidemiological association between prognosis and vitamin D deficit has been described.