Vitamin D and the Immune System. When? Why? How?

Vitamin D, called “the sunshine vitamin” is essential for the good functioning of the human body. Vitamin D generates its principal effects via the vitamin D receptor (VDR), a specific zinc-finger nuclear receptor, located primarily in the nuclei of target cells. VDR is present in most tissues and cells in the body such as in the: digestive system, cardiovascular system, immune system. This receptor represents the key to the understanding of vitamin D non-skeletal effects. Recently, some data were published on the correlation between vitamin D levels and sepsis, indicating a prevalence of vitamin D deficiency of approximately 61.6% in sepsis patients and of 74% in patients admitted to intensive care units (ICU). Vitamin D deficiency in critically ill patients is associated with infection and sepsis, and this association is based on the relation between vitamin D and inflammatory cytokine. Vitamin D, via VDR influences the secretion of cytokines and antimicrobial peptides. Practically, vitamin D acts as an immunomodulator stimulating the differentiation of cells of the innate immune system and, regulating T and B cell proliferation. The data clearly show predominant effects of vitamin D on the adaptive immune function. Vitamin D modulates the T cell phenotype specially that of CD4+ helper T cells (Th1, Th2, as well as Th17 sub-grups). The amplitude of the response to vitamin D depends on a cell’s state of activation, as the number of VDR in inactive cells is low, but may increase five times after activation It was found that the intestinal expression of VDR regulates the host’s microbiome and mediates the anti-inflammatory effects of probiotics. A low level of vitamin D in ICU patients is demonstrated and has many causes. The rapid correction of this deficiency by administering very high doses of vitamin D is possible without causing adverse effects like hypercalcemia or hypercalciuria. Vitamin D is more than just a vitamin. It has clear effects on the immune system, in particular in patients with autoimmune diseases and critically ill. Currently, the majority of data strongly support the association, between low vitamin D levels and sepsis rather than a causal relation. Vitamin D is emerging as a promising and relatively safe nutrient for developing new preventive strategies and adjuvant treatments of diseases, caused by impaired immune-homeostasis. In addition, its supplmentation is very easy and safe.