People who have low levels of vitamin D circulating in their bodies appear to be more vulnerable to COVID-19. In addition, some experts hypothesize that adequate amounts of vitamin D can help protect against inflammation and immune system overreactions. A recent study of high dose vitamin D suggests, however, that it is not a panacea (MedRxiv, Nov. 17, 2020).
High Dose Vitamin D vs. Placebo:
In Brazil, investigators gave hospitalized COVID patients 200,000 International Units of vitamin D3 or placebo. This is a whopping dose. The study was relatively small, including 240 people with severe COVID-19 between June and October 2020.
Unfortunately, the COVID patients did not benefit from the high dose vitamin D. Their hospitalization stays were no shorter. Moreover, they were just as likely as the patients who got placebo to require intensive care or ventilator therapy. Even more important, there was no difference in the proportion of patients who died from COVID-19.
This research has been posted as a pre-print, so it has not been peer-reviewed. However, we can reasonably assume that if a very high dose of vitamin D would make a difference in the infection, this randomized controlled trial would have revealed it.