Is Vitamin D Supplementation Protective Against Coronavirus Disease 2019 (Covid-19)?

Vitamin D, through various mechanisms, affects the immune system, resulting in antiviral effects. Recent studies have also shown that it is effective and safe in the prevention of acute respiratory infections. For this reason, in the era of Coronavirus Disease 2019 pandemic (COVID-19), it is speculated whether vitamin D may also have a positive effect in the course of COVID-19. However, the results of available studies are contradictory, although due to the safety of vitamin D, as well as the information known so far, its regular supplementation in people at risk of deficiency seems to be reasonable.