According to last research, receptors for vitamin D are found in many organs and tissues. Vitamin D deficiency leads to the development of pathological conditions in children and adults. The non-classical effects of vitamin D are important in modulating congenital and acquired immunity, regulating cell proliferation, in the progress of diabetes, the pathology of the cardiovascular system, and autoimmune diseases. The inverse correlation between the level of 25(OH)D3 and the incidence of cancer has been determined. Vitamin D affects the course of pregnancy, and the decidual and placental tissues synthesize 1.25(OH)2D. Vitamin deficiency is found in pregnant women with preeclampsia and gestational diabetes. Timely diagnosis and adequate correction of the level of vitamin D in the blood reduces the risk of developing diseases.