Background: Due to the coronavirus disease 2019 (COVID-19) pandemic, researchers began to investigate the immunomodulatory function of vitamin D more intensively. Researchers suggested that the cytokine storm, that comes with the disease severity and its consequences can be reduced or even prevented with the daily use of vitamin D. The new coronavirus enters the host cell by attaching to the angiotensin converting enzyme 2 receptor and thus damaging lung cells. Vitamin D can play an important role in this step, as it stimulates the expression of the receptor and thus reduces lung cells damage because of SARS-CoV-2.
Aim: The purpose of this master's thesis is to study the effect of the concentration of vitamin D in the blood on the likelihood of infection with the SARS-CoV-2 virus, the course or severity of COVID-19 disease and the effect of vitamin D supplementation on the course of the disease.
Methods: We performed a systematic review of research results on the role of vitamin D in COVID-19. PUBMED, Web of Science and Google Scholar were the databases where we were searching for the studies made. The selection was carried out using an inclusion and exclusion criteria, in accordance with the PRISMA guidelines. We selected studies conducted in 2020 that included data on vitamin D levels in blood before, during and/or after infection with the novel coronavirus and that compared their data with the likelihood of SARS-CoV-2 infection and disease severity. We also included some studies examining the effect of vitamin D as a supportive treatment for COVID-19.
Results: In accordance with the PRISMA guidelines, we selected 27 studies that met our inclusion criteria. We first made analysis of the studies by country, in which they were conducted, by the month of publication, number of participants and design of the study. We than presented the main features of each study, including the association between the vitamin D and the likelihood of infection, disease severity and the effect of adding daily or bolus doses of vitamin D. Deficit or hypovitaminosis was found in the most patients included in the studies, which was linked with the likelihood of infection and disease severity. Both, daily and bolus supplementation were found to influence the course of COVID-19, with the emphasis on daily lower doses.
Conclusion: The results report that there is an association between vitamin D levels in the blood and COVID-19. Vitamin D is a possible choice to prevent COVID-19. Its impact and benefits, however, need to be examined for quantitative results through additional, extensive, randomized clinical trials.
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