Vitamin D is classified as the compounds characterized by multi-dimensional biological activity. For centuries it was thought to be a factor regulating calcium-phosphate metabolism and determines proper bone structure. Last decade studies have discovered a new and broad spectrum of action of vitamin D in the human body. It plays an important role in cell proliferation, angiogenesis, cell differentiation and apoptosis. At present, the phenomenon of vitamin D deficiency is a widespread health problem, which is considered as a pandemic. The fundamental cause is the insufficient human exposure to solar radiation, which is the main source of vitamin D for most people. Its deficiency causes rickets in children and is associated with an increased risk of hypertension, multiple sclerosis, cancer of the colon, prostate, breast and ovary, as well as type 1 diabetes.

Key words: vitamin D, deficiency, calcitriol, pediatric.