At the beginning of the COVID-19 pandemic, we already knew that vitamin D helps reduce the risk of respiratory infections, especially when given to people who are deficient.1 We also knew that it helps us make antimicrobial peptides, and that it simultaneously boosts our immune system’s ability to fight viruses and bacteria while dampening the excessive or dysfunctional activities of our immune system that can lead to autoimmune disease.2
Nevertheless, it didn’t automatically follow from this that vitamin D would reduce the risk of COVID-19. Viruses regularly hijack good things within our bodies to use them against us. It is therefore entirely possible a virus could hijack things made with the help of vitamin D and use those things against us.
