Much has been uncovered regarding the risk factors for contracting Covid-19 and for being harshly effected by its symptoms. Yet, little is known regarding any protective factors that could possibly improve outcomes once the virus is contracted.
It has been shown that vitamin D protects against acute respiratory tract infections. Calcitriol (1,25-dihydroxyvitamin D3) plays an important role in the expression of ACE-2 in the lungs, specifically in the ACE2/Ang(1-7)/MasR axis. It is now known that ACE-2 is the host cell for the entry of the SARS-CoV-2 virus into the human body.
In the past weeks, a negative correlation has been seen between serum levels of vitamin D and European countries most affected by the Covid-19 pandemic. The European Calcified Tissue Society Working Group defines severe vitamin D deficiency as serum 25(OH) D levels lower than 30nmol/L. Spain has shown mean levels of vitamin D levels of 26nmol/L, Italy – 28nmol/L and 45nmol/L in Nordic countries. In Italy specifically, 76% of women over the age of 70 have serum levels below 30nmol/L. In populations older than 70 years, vitamin D levels drastically drop due to lower sun exposure and lower synthesis in the skin. Moreover, in animal studies, ACE-2 levels have been shown to dramatically drop by 67% in older females and by 78% in older males. This parallels the increased mortality rate due to Covid-19 in males as compared to females.
Vitamin D deficiency lowers the ability of macrophages to mature and produce lysosomal enzyme acid phosphatase, critical for antimicrobial protection. Furthermore, vitamin D plays an integral role in the function of toll-like receptors, which recognize pathogens and release cytokines or antimicrobial peptides. The devastating symptoms of Covid-19 are caused in part due to the surge release of pro-inflammatory cytokines. Vitamin D modulates this release and prevents a cytokine and chemokine surge.
This relationship has been demonstrated in other respiratory diseases. Lung injury caused by the H5N1 flu can be alleviated by administration of recombinant human ACE-2 proteins. In fact, higher ACE-2 levels are associated with better outcomes for other coronavirus infections, as ACE-2 protects against lung injury.
This negative correlation between vitamin D levels and mortality due to Covid-19 is a crude relationship. However, we are beginning to see research in protective factors against the disease. As many dental offices are slowly beginning to get back to work, any scientific evidence to minimize transmission and symptoms is essential.
