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.
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, https://doi.org/10.1093/jn/nxaa233.
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