The Role of Vitamin D in Supporting Health in the COVID-19 Era.

The genomic activity of vitamin D is associated with metabolic effects, and the hormone has a strong impact on several physiological functions and, therefore, on health. Among its renowned functions, vitamin D is an immunomodulator and a molecule with an anti-inflammatory effect, and, recently, it has been much studied in relation to its response against viral infections, especially against COVID-19. This review aims to take stock of the correlation studies between vitamin D deficiency and increased risks of severe COVID-19 disease and, similarly, between vitamin D deficiency and acute respiratory distress syndrome. Based on this evidence, supplementation with vitamin D has been tested in clinical trials, and the results are discussed. Finally, this study includes a biochemical analysis on the effects of vitamin D in the body's defense mechanisms against viral infection. In particular, the antioxidant and anti-inflammatory functions are considered in relation to energy metabolism, and the potential, beneficial effect of vitamin D in COVID-19 is described, with discussion of its influence on different biochemical pathways. The proposed, broader view of vitamin D activity could support a better-integrated approach in supplementation strategies against severe COVID-19, which could be valuable in a near future of living with an infection becoming endemic.

Vitamin D and Beta-Glucans Synergically Stimulate Human Macrophage Activity.

Vitamin D and beta-glucans are both immunostimulants. Vitamin D exerts its beneficial effects on many components of the immune system. In macrophages, the hormone modulates both phagocytic activity and cytokine production; therefore, it plays an important role in mediating the innate immune response to infection. The immunomodulatory properties of beta-glucans are attributed to the ability of these fungal cell wall polysaccharides to bind to different receptors expressed on the cell surface of phagocytic and cytotoxic innate immune cells, including monocytes and macrophages. The intracellular signaling pathways activated by beta-glucans lead to enhanced phagocytosis and cytokine response. In this study we investigated the possible potentiation of immunomodulatory properties of the combined treatment with vitamin D and beta-glucans. The effects of 100 nM 1,25-dihydroxyvitamin D3 or 100 µg/mL beta-glucans were evaluated in human macrophages in terms of cytokine production, intracellular vesicle acidification and changes in energy metabolism, three hallmarks of macrophage antimicrobial activation. We found that all the analyzed parameters were enhanced by the co-treatment compared to the response to single molecules. The results of this study support the validity of a novel therapeutic approach that could boost the immune response, taking advantage of the synergy between two natural compounds.