Important health-related benefits associated with vitamin D have long been recognized.  In addition to bone health, vitamin D has a beneficial effect on the immune system and, therefore, may protect against viral infections. In fact, vitamin D status may, in part, account for observed population differences in COVID-19 infection rates and severity. The mechanisms and characteristics that make some individuals more or less susceptible to severe COVID-19 symptoms remain unclear.  Drs. Sara Zwart (University of Texas Medical Branch) and Scott Smith (NASA Johnson Space Center) provide a short review, published in The Journal of Nutrition, regarding vitamin D status and the severity of the immune response to SARS-CoV-2, the virus that is causing the coronavirus disease 2019 (COVID-19). 

How could vitamin D status possibly affect SARS-CoV-2 severity and mortality? The answer may be related to a myriad of signaling actions coordinated by vitamin D.  Vitamin D can influence the immune system in a number of ways, including decreasing production of inflammatory signaling molecules as well as increasing production of those with anti-inflammatory actions.  Because SARS-CoV-2 infections result in an aggressive inflammatory response, it is possible that adequate vitamin D status may blunt the production of inflammatory signaling molecules.

Similar to other viral infections, there is some evidence that individuals can test positive despite earlier recovery from SARS-CoV-2 infection. Therefore, it is possible that in some individuals the virus may persist in the body due to slower viral clearance. Studying astronauts during spaceflight has provided a novel approach to better understand viral reactivation in healthy individuals who are exposed to environmental and psychological stressors. 

Vitamin D actions on the RAS. The figure summarizes how vitamin D can act on the RAS to promote tissue protection from SARS-CoV-2 infection. ACE2 is the primary entry point into cells, and SARS-CoV-2 downregulates expression, promoting tissue injury. Vitamin D is a negative endocrine RAS modulator and can increase expression and concentration of ACE2, having a potentially protective role against tissue injury. ACE2, angiotensin-converting enzyme 2; RAS, renin-angiotensin system; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2.

Factors that influence viral reactivation in spaceflight include cardiorespiratory fitness level, skeletal muscle endurance, stress, and stress combined with vitamin D status. Astronauts with greater cardiorespiratory fitness had a 29% less risk of viral reactivation.  Similarly, in a vitamin D supplementation study, subjects wintering over in Antarctica with lower vitamin D status and higher levels of a stress hormone experienced greater viral shedding in their saliva than did subjects with higher vitamin D concentrations.  These data suggest that higher vitamin D status, along with physical fitness, may help protect against reactivation of latent viruses in high-stress environments.

While it is unlikely that there is a single solution that will end the COVID-19 pandemic, these evidence-based studies suggest maintaining vitamin D status may be an important consideration to reduce the risk of severe response to SARS-CoV-2 infection and/or viral reactivation.  The authors concluded that it is important that people maintain optimal vitamin D status to support immune function and lower their risk of viral reactivation. Modifiable measures such as these may have the potential to safely and easily offer some protection against SARS-CoV-2 infection.

References Zwart SR, Smith SM. Vitamin D and COVID-19: Lessons from Spaceflight Analogs. The Journal of Nutrition, Volume 150, Issue 10, October 2020, Pages 2624–2627,

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