The biological system of vitamin D comprises active metabolites, enzymes and receptors that give rise to genomic and non-genomic effects at a systemic level. In addition to its impact on the health and attributes of the musculoskeletal system, the vitamin D system has been shown to influence numerous physiological functions at a level of the metabolism and the cardiovascular system. For some time now, important effects of vitamin D and its metabolites on the immune system and its dependent inflammatory reactions have also been acknowledged. The recent outbreak of the COVID-19 pandemic has engaged numerous research centres in an attempt to highlight the possible role of vitamin D in relation to susceptibility to infection, clinical expression of the disease and its clinical course. The aim of this brief review is to summarise the state of knowledge on the role of vitamin D in relation to immunity and inflammation, with particular emphasis on what we have learned so far in relation to its impact on the SARS-CoV-2 infection, whereas, due to a lack of space, its impact on autoimmune diseases will not be considered.
