Some people will experience minimal effects from COVID-19 because their immune system can efficiently fight off the infection. The "host" factors that promote such a strong immune system were extensively studied before the age of antibiotics, and without an effective vaccine, they should be an important part of today's response to the epidemic. Host factors that are often considered include vitamins (e.g., A and C), minerals (e.g., zinc and magnesium), and the omega-3 fatty acids. Of these, perhaps the most studied and most important host factor impacting survival from COVID-19 is vitamin D, created in skin from exposure to ultraviolet B radiation in sunlight.
Casting Sunlight on an Epidemic
As a public health specialist at the National Institutes of Health, I outlined how a lack of sun-induced vitamin D in the winter and early spring leads to epidemic acute respiratory infections (and this probably includes viruses like COVID-19). That review, cited almost a thousand times, argued that groups with low vitamin D levels -- the obese and the elderly and those with dark skin -- may require 5,000 IU of vitamin D each day to obtain the 25-hydroxyvitamin D levels of 50 ng/mL that appear to protect against viral respiratory infection.
A government-sponsored research strategy to address this issue has not been developed, as officials explained that there was no mandate to explore an alternative to the existing vaccination program. However, other researchers picked up the ball and provided convincing evidence that vitamin D could reduce the incidence of acute respiratory infection.
Vitamin D: Indicated for the Prevention of Acute Respiratory Infection
In 2017, The BMJ released a systematic review and meta-analysis using data from 25 randomized controlled trials. In these studies, the incidence of acute respiratory infection was evaluated in participant-level data from more than 11,000 participants given either vitamin D or placebo. The international team of authors concluded that vitamin D supplementation is safe and that it protects against acute respiratory tract infection. The benefit is greatest in subjects receiving weekly or daily vitamin D, and greatest in those who are deficient.
The study noted that it was necessary to treat only four people who are deficient in vitamin D to prevent one case of acute infection. Critical care research also documents the important effect of vitamin D on survival in ICU patients with acute respiratory distress syndrome. There are several mechanisms by which vitamin D activity is critical for immune defense: vitamin D acts to maintain tight junctions, promote the effect of antimicrobial peptides (i.e., cathelicidin and defensins), and moderate the inflammatory response.
Evidence-Based Prevention
Aggressively identifying and treating people with vitamin D deficiency is one potential strategy to reduce the risk of COVID-19. As outlined in the BMJ review, regularly taking oral vitamin D3 mitigates infection, although the optimal oral dose is debatable. Bolus doses do not appear to provide benefit against infection, possibly through a dysregulation of vitamin D metabolism.
There may be a simple yet effective alternative. Since exposing the whole body to bright sunlight can provide long-lasting and rapid correction of deficiency, this may provide a critical boost to host immune defenses. Lacking definitive research, any risk of exposing the body to sunshine while sheltering in place is clearly outweighed by the risk of COVID-19.
MedPage Today does not endorse vitamin D supplementation for preventing or treating COVID-19. We are publishing this article simply to stimulate discussion and raise awareness of one possible contributor to COVID-19 susceptibility. It should be noted that the BMJ review and meta-analysis cited above did not address efficacy against coronavirus infections (COVID-19, SARS, MERS); additionally, nearly half of the participants in the included studies were infants in India and Afghanistan.
Cdr. John C. Umhau, MD (ret.), was a public health specialist and senior clinical investigator at the National Institutes of Health for over 20 years. The opinions expressed are his own, and do not represent the position of any government agency. Umhau reports that he has no conflicts of interest.