This is a very weak study because it is retrospective: they just looked at existing medical records. And they only found 20 COVID patients that had vitamin D le

This is a very weak study because it is retrospective: they just looked at existing medical records. And they only found 20 COVID patients that had vitamin D levels recorded. But the finding is compelling enough that we should demand better studies. Actually there already is a better study where they actually tested vitamin D levels of many COVID patients [1]. It found vitamin D was strongly associated with less severe outcomes: > Only 26% of the cases had 25(OH)D in the normal range, and virtually all of them (86%) had a mild outcome. ... Just over a third (38%) had 25(OH)D in the insufficient range, and only one of them (1.3%) had a mild outcome. ... Just over a third (36%) had 25(OH)D in the deficient range, and their distribution was pushed further toward severe and critical outcomes. Only one patient (1.4%) had a mild outcome, while 26% had an ordinary outcome, 40% had a severe outcome, and 33% had a critical outcome. Now we should demand a controlled trial where they actually give a vitamin D intervention: this would provide causal evidence. However, avoiding vitamin D deficiency is already very well studied and has so many benefits that I think it is worth everyone's time and effort to do so. Many people are advising high levels of vitamin D supplementation. However, there is reason to not overdo it on vitamin D supplementation and take just 1700 IU/day (or to just get sunshine) [2]. Of course, getting your vitamin D levels tested (with the help of by a doctor) is the safe way to go about this. [1] https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3571484 https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3571484 [2] https://chrismasterjohnphd.com/covid-19/update-on-vitamin-d-and-covid-19-using-the-first-observational-study-released https://chrismasterjohnphd.com/covid-19/update-on-vitamin-d-...