Asthma is one of the most common chronic diseases in childhood and one of the leading causes of morbidity in children. Its incidence has been growing, especially in the Western, highly industrialized nations. Glucocorticoids are used for the treatment of many inflammatory and autoimmune diseases, among them asthma, because they can switch off genes that code for pro- inflammatory cytokines and chemokines. Unfortunately, there is a substantial group of severe asthma patients that are steroid resistant. In addition, they suffer from the long term side effects of systemic steroid use.
Vitamin D3 plays an important role in the maintenance of several organ systems and its deficiency causes multiple and complex dysfunctions for the organism. Vitamin D3 has been originally described to regulate calcemia by absorbing calcium in the intestine and by increasing re-absorption of calcium in the kidneys. Recent studies have shown the important effects of Vitamin D3 on many other systems, especially as a modulator of the immune system, and its deficiency has been linked to several autoimmune and inflammatory diseases such as multiple sclerosis, inflammatory bowel disease, lupus erythematosus, rheumatoid arthritis and asthma.
Vitamin D inhibits the dysregulated antibody synthesis that is seen in asthmatics. It inhibits the proliferation of immune cells that produce inflammatory substances, and conversely, vitamin D enhances the function and proliferation of regulatory cells, through the induction of IL-10 producing T regulatory cells, and a very effective group of T regulatory cells characterized as CD4+ CD25+ FoxP3+ . Dendritic cell (DC) function is also modulated by Vitamin D. 1,25(OH)2vitaminD3 appears to generate tolerogenic dendritic cells (DC) in vivo, as demonstrated in models of transplantation and autoimmune diseases. Immature/tolerogenic DCs induce development of T regulatory cells by several mechanisms, including production of IL-10 or TGF-beta. Vitamin D3 increases the glucocorticoid receptor expression in asthmatic patients' T cells. In an interesting study on an asthma mouse model, treatment with Vitamin D combined with immunotherapy resulted in increased production of the inhibitory cytokine IL-10 in lung tissue and increased levels of TGF-beta in serum.
Overall these studies and others, support the hypothesis that Vitamin D induces regulatory T cells that are crucial for the control of autoimmune diseases such as asthma.
In spite of this attractive conceptual link between the benefits of vitamin D and immune regulation in SR asthma, no study has presented clinical data, i.e., pulmonary functions, quality of life score, reduction in steroid dose and other medications, and indices of better asthma control. There is also a dearth of ex-vivo data in order to confirm or refute in-vitro results. There is very little data that characterizes the effects of vitamin D supplementation on immune cells, cytokines, and asthma mediators.
