et al., The American Journal of Clinical Nutrition, doi:10.1093/ajcn/nqaa381 (Peer Reviewed)
Retrospective 8,297 adults from the UK Biobank showing the habitual use of vitamin D supplements significantly associated with lower risk of COVID-19 cases. Note that the information on vitamin D supplement use was collected a median of 10 years before the COVID-19 tests, so usage may have changed significantly.
Ma et al., 1/29/2021, retrospective, United Kingdom, Europe, peer-reviewed, 4 authors, dosage not specified.
risk of COVID-19 case, 30.0% lower, RR 0.70, p = 0.03, treatment 49 of 363 (13.5%), control 1329 of 7934 (16.8%), adjusted per study, odds ratio converted to relative risk.
Effect extraction follows pre-specified rules
prioritizing more serious outcomes. For an individual study the most serious
outcome may have a smaller number of events and lower statistical signficance,
however this provides the strongest evidence for the most serious outcomes
when combining the results of many trials.