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Vitamin D study #62 of 71
1/29 Pre-Exposure Prophylaxis study (treated before exposed to the virus)
Ma et al., The American Journal of Clinical Nutrition, doi:10.1093/ajcn/nqaa381 (Peer Reviewed)
Habitual use of vitamin D supplements and risk of coronavirus disease 2019 (COVID-19) infection: a prospective study in UK Biobank
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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.
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