Purpose of the study: to analyze the interlinks between serum 25(OH)D level and severity of new coronavirus infection (COVID-19) in hospitalized patients, as well as the effect of adding colecaciferol to standard therapy for patients in the acute period of the disease.

The study will involve at least 300 hospitalized patients with confirmed COVID-19. All study participants will be twice assessed for serum 25 (OH) D levels: baseline and 8-10 days of hospitalization. Following a baseline examination, patients will be randomized into 2 groups. Group I (No. 1), vitamin D therapy begins with a dosage of 50,000 IU in the first and second weeks. Group II (No. 2), vitamin D therapy is prescribed at a dosage of 2000 IU / day. On 8-10 days of vitamin D supplementation, all participants will be retested for serum 25 (OH) D levels to assess the effectiveness of therapy. On 14-21 days we assessed severity of the course, ICU hospitalization, duration of hospitalization, outcome of the disease, duration of glucocorticoid therapy, the need for specific therapy (inhibitors IL-6), changes in cytokine/chemokine, APPs concentration.

The COVID-19 pandemic that swept the world in 2019 radically changed not only the social sphere of life, subordinating everything around to its influence, but also the healthcare sector. It affected both its practical and scientific sides, globally changing the approach to medicine. Numerous studies around the globe are being conducted on the prevention and treatment of this infection. A significant amount of them study the role of vitamin D in the pathogenesis of the disease. Cholecalciferol (Vitamin D) is a fat-soluble vitamin that is involved in maintaining the serum calcium-phosphorus gradient. Vitamin D supplementation significantly reduces the risk of osteoporosis, and also affects the regulation of immune responses by modulating innate and adaptive immune responses. It has been shown to inhibit the proliferation of T cells, namely the subsequent transformation of Th1 cells to Th2 cells. This effect on cell proliferation and differentiation contributes to a significant decrease in the level of proinflammatory cytokines, thereby reducing the severity of immune-mediated damage. It was these mechanisms that formed the basis of the theory about the ability of vitamin D to prevent the severe course of coronavirus infection and even prevent it. At the moment, the effect of vitamin D on reducing COVID-19 morbidity is not fully confirmed.

Inclusion Criteria:

• males and females aged 18 to 75 years
• who did not take Vitamin D supplementation
• COVID-19 clinical features
• signed informed consent to participate in the research.

Exclusion Criteria:

• pregnancy or nursing
• primary hyperparathyroidism or hypercalcemia other etiologies (including 24-hydroxylase mutation)
• a history of granulomatous diseases
• severe gastrointestinal diseases (clinically apparent malabsorption syndrome)
• liver disease
• kidney disease
• individual intolerance drug
• vitamin D supplementation in a dose of more than 800 IU per
• drugs known to affect vitamin D metabolism (e.g., anticonvulsants, glucocorticoids, diuretics)
• alcohol and drug addiction.
• history of cancer (less than 5 years)