Evaluation of Deficiency of Vitamin D and Advantages of Supplementation of Vitamin D in COVID-19 Infections: A Narrative Review.

Continuously evolving literature has helped to understand the vitamin D contribution to the coronavirus disease 2019 (COVID-19) manifestations and the associated clinical outcomes in different patient populations. Evidence suggests a widespread occurrence of deficiency of vitamin D among patients presenting COVID-19 and a possible link between vitamin D insufficiency and disease progression or mortality. Furthermore, studies worldwide have reported that supplements of vitamin D have a beneficial effect on COVID-19 outcomes. Contradictory data, however, suggest that there is no association between levels of vitamin D and the likelihood of COVID-19 infections. Therefore, a comprehensive search of the published literature is conducted to better understand any harmful effects of vitamin D deficiency (VDD), advantages of vitamin D supplementation, and the relationship between status of vitamin D and risk, severity, and mortality in patients with COVID-19. The information was gathered from the PubMed database published between January 2020 and July 2022 regarding the function of vitamin D in the immune system, the link between deficiency of vitamin D and COVID-19 infection, severity, risk of mortality of COVID-19, and the impact of vitamin D treatment on outcomes of COVID-19. Vitamin D modulates the immune system by elevating the levels of cathelicidins and β-defensin in the body. Deficiency of vitamin D is markedly attributed to the risk of acute respiratory distress syndrome (ARDS), which determines the severity of disease in patients with COVID-19. Levels of vitamin D below 20 ng/mL in patients with COVID-19 are linked to an increased mortality and morbidity. Vitamin D concentration of >30 ng/mL can diminish the COVID-19 severity and risk of mortality. Supplementation with vitamin D to maintain a serum concentration of 30 ng/mL would mitigate the incidence of COVID-19 and poor prognostic outcomes.