I note with some concern that in the 5 months since this fine article was published, nobody has cared enough to comment here. And on the same page with this article, there is a link for another article saying that "Vitamin D3 supplementation shows no therapeutic benefits in severe COVID-19 patients, study finds" - as we have seen with hydroxychloroquine, doubtless many people will see that and assume that the correct conclusion is that vitamin D is of no value at any stage of the disease. IMHO it is mostly mistakes like that which have killed a lot of us - along with state governors in the USA who have kept people trapped in nursing homes to catch the disease. We have heard more about zinc than magnesium, and it would be interesting to see a direct comparison of the two elements, more or less neighbors in the periodic table. An interesting comment on another publication suggested that we should look at supplementing more than one dietary material, including vitamin C and D and  zinc and selenium, on the basis that the incoming patient may be deficient in some or all of those. That seems reasonable to me, whatever the patient needs, give them some of that; but some of the criticism of hydroxychloroquine on the basis that the patients were given something else at the same time appears to be rejecting both medicines. A more logical conclusion might be that we should continue to use whatever works, and perhaps (unless it becomes clear that the dire fate of the placebo group means that it would be unethical to withhold the successful materials from them) continue with clinical trials to find out more about the individual materials. I have been saying for some time that we are finding out things about health care that we will not like - apparently including a bias in favor of inactivity. It seems to be more important to reject anything that seems promising, than to save the lives of the humans who have the disease. You have some advantage, being outside the USA and insulated to some extent against our political problems, which have contributed to our lack of success. I look forward to seeing more of your work.