[kpfleger]

As with many comments in this thread, carefully reading the originally linked review: http://agingbiotech.info/vitamindcovid19/ would help. One of the 3 recent preprints specifically noted repeated testing of C19 patients and they did an ANOVA statistical test and determined that D blood levels were not declining in the patients over the course of the infection.

This doesn't prove causality, but it rules out the reverse causality you hypothesize in this post. There is a good, concise (3-paragraph) sub-section on the causality question in the discussion section called "Correlational data supported by many pieces of causal evidence". Mandatory reading for anyone who reacts with "correlation doesn't imply causation" as a criticism. Karl (author of the review)