This study in PLOS One is being reported (and used by a lot of people on twitter) as proving definitively that Vitamin D supplementation can treat COVID-19 So, thought I'd do a peer-review on twitter 1/npic.twitter.com/bIsYSKdmjj
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9/n If we look just at the patients who the authors found a significant relationship for - those over 40 - you can kind of see a relationship but it's VERY slimpic.twitter.com/pOAWPvWpex
10/n And when you look at all of the other outcomes the authors analyzed, a similar pattern emerges Low vit D increased the risk of hypoxia, but not shortness of breath. It DECREASED (not significantly) the risk of chest painpic.twitter.com/ZTeL7a5tGC
11/n You could write this study up as demonstrating that there was no correlation between vit D and most COVID-19 outcomes, and therefore we still don't know if it does anything for the disease
12/n Instead, the authors use the pretty tenuous observational link between low vit D in people over 40 and death to posit that supplementation should be used for all patients which isn't really supported by their resultspic.twitter.com/y5tkjFnXOZ
13/n While I could go into the results a bit more - the statistical analysis is a little bit meaningless, the confounding factors not really even considered - but honestly there's not really much point I think
14/n The results show a vague correlation between vit D and some outcomes, with a smattering of statistical significance if you run the analyses in certain ways Not much that you can take away from that, I think
15/n If nothing else, the small sample size makes it hard to conclude anything from these results other than "we need BETTER research"
Slim is an understaement
Correlation does not prove causation. 
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