REN and COVID-19: One of the vitamins that has attracted the most attention in relation to COVID-19 is vitamin D. The importance of a sufficient concentration of this vitamin in relation to COVID-19 is due to its potential immunomodulatory effects such as maintenance of epithelial cell integrity, promotion of antimicrobial peptides, modulation of antigenic presentation by dendritic cells, promotion of anti-inflammatory cytokines, and regulation of renin production [9].