The theoretical part of the diploma thesis on the topic "Vitamin D" is devoted to the problems of vitamin D in the present days and in the past, describes the role of this in terms of biochemistry and physiology, which factors (enzymes, receptors) are involved. The paper presents the value of vitamin D for the human body, its main exogenous and endogenous sources. It also discusses the regulation of vitamin D in the body, the effect on individual organs and organ systems, determines the optimal intake doses, the need for nutritional supplements and the health risks related to hypovitaminosis. Certain diseases of the musculoskeletal system, heart and gastrointestinal tract, which are caused by a violation of homeostasis of the vitamin D. The purpose of the experimental part is to analyze a group of 50 patients, the results of their laboratory studies from the Hustopeče hospital at the Department of Clinical Biochemistry and Hematology (OKBH), in order to verify if there is any relationship between vitamin D and C-reactive protein, alanine aminotransferase, patient weight and their place of work.