Vitamins, microelements and the immune system: current standpoint in the fight against coronavirus disease 2019

Coronavirus disease 2019 (COVID-19) is an acute respiratory disease associated with severe systemic inflammation. The optimal status of vitamins and microelements is considered crucial for the proper functioning of the immune system and necessary for successful recovery. Most patients with respiratory distress in COVID-19 are vitamin and microelement deficient, with vitamin D and Se deficiency being the most common. Anyway, various micronutrient supplements are widely and arbitrarily used for prevention or in the treatment of COVID-19. We aimed to summarise current knowledge about molecular and physiological mechanisms of vitamins (D, A, C, B₆, B₉ and B₁₂) and microelements (Se, Zn, Cu and Fe) involved in the immune system regulation in consideration with COVID-19 pathogenesis, as well as recent findings related to their usage and effects in the prevention and treatment of COVID-19. In the early course of the pandemic, several, mainly observational, studies reported an association of some micronutrients, such as vitamin C, D and Zn, with severity reduction and survival improvement. Still, emerging randomised controlled trials showed no effect of vitamin D on hospitalisation length and no effect of vitamin C and Zn on symptom reduction. Up to date, there is evidence neither for nor against the use of micronutrients in the treatment of COVID-19. The doses that exceed the recommended for the general population and age group should not be used, except in clinical trials. Benefits of supplementation are primarily expected in populations prone to micronutrient deficiencies, who are, as well, at a higher risk of worse outcomes in COVID-19.