Are there real randomized controlled trials? Yes – three of them. One from Spain (n = 76) tried randomizing hospital patients to get or not get Vitamin D; the patients in the experimental group did much much much better (25x lower odds of having to go to the ICU!) than the control group. Another from India (n = 40) tested asymptomatic people with mild cases; everyone stayed mild but the patients treated with Vitamin D were three times more likely to clear the infection quickly. The last, from Brazil (n = 240) was a large multicenter RCT that tested whether Vitamin D affected the outcomes of hospital patients. It found no effect whatsoever, not even a hint of a trend.
I could take or leave the Indian trial; nobody is worrying very much about seroconversion in mild cases. The Spanish and Brazilian ones are a pretty jarring contrast. In the Spanish one, the Vitamin D treated patients did 25x better; in the Brazilian one, there was no benefit at all.
I side with Brazil. It’s bigger, more professionally-done, and has fewer minor statistical flaws that really shouldn’t matter this much but make me nervous. Also, in the past I have learned to side with negative RCTs rather than astoundingly massively positive ones when the two conflict. There were some early astoundingly massively positive RCTs for hydroxychloroquine, and then the bigger and more-professionally-done ones that came later showed no effect.
Author(s): Scott Alexander
Publication Date: 16 February 2021
Publication Site: Astral Codex Ten at Substack