Vitamin D plays an import role in the regulation of calcium-phosphorus metabolism, metabolic processes and the cell cycle.Over the years, the mechanisms of molecular action of vitamin D in various cells, organs and tissues have been well studied. The widespread prevalence of vitamin D deficiency, established on the basis of laboratory diagnostics, has led to the development and implementation of programs for the correction of hypovitaminosis D. However, the question of the clinical effectiveness of these programs remains open. In this article, we review studies and meta-analyses of data that have assessed the preventive and therapeutic efficacy and safety of physiological and high doses of vitamin D.