Israel Medical Association Journal

Vitamin D deficiency is becoming an increasing problem worldwide. It should not be underestimated, not only due to the well-known consequences vitamin D deficiency has on bone health, but primarily because recent studies have shown how the biologically active form of vitamin D – 1,25(OH)2D – is involved in many biological processes, including immune system modulation. Moreover, the presence of a vitamin D receptor was discovered in almost all immune cells and some of its polymorphisms were found to be associated with increased incidence of autoimmune diseases. This finding led to a proposed link between vitamin D deficiency and autoimmune diseases. Patients affected by various autoimmune diseases showed low levels of vitamin D. However, it is not always clear whether vitamin D deficiency is the cause or rather a consequence of the disease. Limitations of the studies, such as the small number of patients, heterogeneity of selected groups, environmental conditions, methods used to measure vitamin D serum concentration and other confounding factors do not lead to unequivocal results to demonstrate a direct link between low vitamin D levels and autoimmune disease. Therefore, randomized trials are needed to clarify conflicting results.

Autoimmune diseases constitute a diverse group of disorders characterized by cellular and humoral responses against self. The humoral autoimmune responses are directed against various cellular and extracellular components. These responses are highly specific for each autoimmune disease and result in the production of autoantibodies that characterize certain disease entities, representing a valuable tool for the diagnosis of autoimmune diseases. Furthermore, certain autoantibodies are helpful in the prognosis of disease development, progression and severity, as well as in the classification of patients with distinct disease subtypes. Today, the value of autoantibodies in the follow-up of patients is limited, but preliminary data suggest that they may be useful in predicting response to treatment. 

There is growing interest in the contribution of vitamin D deficiency to autoimmunity. Several studies have shown an association between low levels of vitamin D and autoimmune disorders, including multiple sclerosis, rheumatoid arthritis, type 1 diabetes, autoimmune thyroid diseases, celiac disease, and systemic lupus erythematosus (SLE). Vitamin D receptor ligands can mediate immunosuppressive effects. It has been suggested that low levels of this hormone contribute to the immune activation in lupus and other autoimmune diseases. This review updates and summarizes the literature on the association between vitamin D and SLE, and discusses the various correlations between vitamin D and SLE activity, clinical expressions, serology, and gene polymorphisms of vitamin D receptors.