Vitamin D and its emerging role in immunopathology

In recent years, there has been an increased recognition that vitamin D is not only a risk factor for poor musculoskeletal health but also a possible important contributor in the development of different autoimmune diseases. This has been linked to multiple immunosuppressive properties of vitamin D. Vitamin D has got pleiotropic effects and this reflects the wide spread presence of vitamin D receptors (VDRs) throughout the body. Currently, there is much ongoing research with regard to its emerging role in immunopathology. VDR has not only been found in tissues involved in calcium homeostasis but also in a variety of cell lines involved primarily in immune regulation, e.g., mononuclear cells, dendritic cells, antigen-presenting cells, and activated B lymphocytes and CD4+ T cells. There have been several reports linking the presence of low vitamin D to various autoimmune diseases. However, for autoimmune/inflammatory disease outcomes, firm conclusions regarding cause and effect cannot be based on epidemiological association studies, and prospective, long-term, well-designed studies, including large intervention trials, are needed across all life stages. In this paper, we will describe the evidence base for this potential role of vitamin D in different aspects of autoimmune diseases. Because of the enormous breadth of this emerging field, our aim in this review is not to provide an exhaustive list of all literature pertinent to vitamin D and immunopathology. Instead, we will frame the reasons and rationale behind the development of several immunoregulatory activities for 1,25(OH)2D3.