In the twenty-first century, we are constantly facing allergic diseases, autoimmune diseases and cancers. Despite the genetic predisposition to the above-mentioned diseases, there is a possibility of supporting the organism with substances with immunomodulatory properties, such as vitamin D. Although it has been knownso far mainly for the regulation of calcium and phosphate metabolism, its role in supporting the immune system is being discovered. The evidence for this is the demonstration that genes regulated by vitamin Dencode proteins involved in the processes of cell differentiation, proliferation and apoptosis and the detection of vitamin D receptors in cells of the immune system – thymus, B and T lymphocytes and bone marrow. Vitamin D occurs in foods of animal origin in the form of cholecalciferol, and in plant products in the ergocalciferol form. Cholecalciferol can also be obtained through the synthesis by
human skin under the influence of UVB radiation. In Poland, there is a common deficiency of vitamin D – during summer, on average, 50% of the population is deficient, while in the winter, this percentage increases to 80%. The deficiency may predispose to many diseases. The objective of this paper was to examine the potential impact of vitamin D in terms of preventing and/or improving selected autoimmune and allergic diseases. Clinical studies in the scientific literature have been analyzed to determine the influence of vitamin D supplementation on the prevention and/or course of cancer in adults, autoimmune diseases in adults, and allergic diseases in children and adults. The conclusions are based on a meta-analysis of 8 clinical studies and 1 in vitro study on cell culture. The results of the study show that the compensation of 25(OH)D deficiency results in a milder course of systemic lupus erythematosus and Hashimoto’s disease. The supplementation of at least 1,200 IU of vitamin D reduces the incidence of cancer by an average of 35% among adults at risk compared to people without supplementation. The recommended intake of vitamin D by pregnant women also reduces the risk of allergic diseases in children from age 1 to 10. Moreover, vitamin D (2000 IU) supplementation in adults suffering from asthma supports a milder course of asthma and reduces the incidence of upper respiratory tract infections compared to the group not using supplementation.
