Most people are vitD deficient, up to 77% of the population (Ginde et al 2009), which may increase risk in COVID-19. Deficient is defined as vitD blood levels <30 ng/ml; far below the optimal range of 50-100 ng/ml.

VitD affects immune system function by:

1- Increasing cathelicidin, an antimicrobial peptide that is produced in mucosal epithelium (nasal, throat, lung, intestinal tissue) and skin. Cathelicidin kills bacteria, fungi and VIRUSES. Cathelicidin (which is regulated by vitD) is the first line of defense against infectious agents.

-INCREASING anti-inflammatory cytokines (immune cells) such as interleukin-10 and DECREASING pro-inflammatory cytokines such as Tumor Necrosis Factor TNF and interferons.

Cathelicidin protects from infection while the cytokines defend the body to rid it of infection should infection occur. Both 1 and 2 are dependent upon vitamin D to function correctly. An overexpression (overproduction) of pro-inflammatory cytokines appears to be a factor in the immune storm that ultimately kills COVID-19 victims.