ABSTRACT
Resume. The article discusses diseases that depend on the level of vitamin D in the body, possible methods of correcting its level and their consequences. The dependence of the body on the level of this vitamin in the blood is considered. At the moment, there is a global vitamin D deficiency worldwide, which was revealed during the global COVID-19 pandemic. The positive effect of vitamin D on the immune system has been proven, and therefore its deficiency can worsen the course of various diseases. Vitamin D also acts as a hormone, the lack of which leads to pathologies of the cardiovascular system, rickets, osteoporosis, diabetes, obesity, and other serious diseases. The influence of its level on postoperative recovery is also considered. In addition, the article provides methods of correction by means of UV treatment in winter, which, as the data has shown, is dangerous. The article describes neurodegenerative disorders, which are greatly influenced by the level of this vitamin and its prevention. The influence of its level on the health of postmenopausal patients, leading to undesirable consequences, including osteoporosis, is analyzed. Examples of the effect on the protective properties of the oral cavity in periodontal disease and caries are given. The article describes the effect on the course of acute respiratory diseases in children, as well as the effect on the course of the disease in diabetes mellitus.