The authors claimed to have found that calcifediol (a byproduct of vitamin D) reduced the risk of mortality in covid-19 patients hospitalized in Spain by a whopping 60% compared to people given standard care.
For comparison, the arthritis drug tocilizumab was recently found to reduce mortality in severe covid-19 patients by 4% in a large UK trial—modest results that are promising enough to likely enshrine it as a standard treatment along steroids for critical cases.