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Vitamin D is a fat soluble vitamin and a steroid hormone with endocrine, paracrine and autocrine actions. The two major forms are vitamin D2 (ergocalcifeol) and vitamin D3 (cholecalciferol), the active hormone being calcitriol. The importance of vitamin D and its metabolites lies in the key role in calcium homeostasis and bone metabolism but vitamin D also has extraskeletal effects, still incompletely understood. Vitamin D receptor (VDR) is ubiquitous in the body, the presence of VDR in multiple tissues suggesting a more general role of calcitriol. Vitamin D can regulate many cellular functions such as cell proliferation, differentiation, and apoptosis. Calcitriol exerts immunomodulating and antiproliferative effects and plays a potential role in the prevention and therapy of various cancers (breast, colorectal, prostate, thyroid), autoimmune diseases (rheumatoid arthritis, systemic lupus erythematosus, inflammatory bowel disease, multiple sclerosis and type 1 diabetes, thyroid autoimmunity), obesity and also in cardiovascular, renal, maternal-fetal pathologies. Conclusions. The current studies bring increasingly more evidence about the benefits of vitamin D supplementation in extraskeletal pathology although there is no agreed protocol in this regard. However, these patients should be considered for adequate intake of vitamin D for the prevention, improving the evolution and the prognosis of their disease. [ABSTRACT FROM AUTHOR]