Vitamin D Supplementation and Clinical Outcomes in Severe COVID-19 Patients

Single center, open label randomized clinical trial. Study location: tertiary hospital center (University Hospital Split, Croatia). All COVID-19 patients with positive PCR test admitted to ICU and in need for respiratory support will be eligible for inclusion in this study. Patients admitted to ICU with severe COVID-19 disease and in need for invasive or non-invasive respiratory support with low levels of vitamin D (\ 150 nmol/l or if the calcium levels are consistently \> 2.6 mmol/l, further supplementation will be stopped. Outcomes: Primary outcome is number of days spent on ventilator. Secondary outcomes: all-cause mortality on day 28, all-cause mortality on day 60, mortality at hospital discharge, clinical improvement at day 28 (WHO clinical progression scale), days spent in ICU, days spent in hospital after discharge from ICU, need for dialysis at day 28, bacterial superinfections, neutrophile to lymphocyte ratio, disease severity (CRP levels, PaO2/FiO2 ratio, D-dimer levels, fibrinogen, ferritin, PCT), adverse outcomes. Hypothesis: patients receiving Vitamin D supplementation will have shorter number of days spent on mechanical ventilation.