Abstract: Journal Pre-proof Efficacy and Safety of Vitamin D Supplementation to Prevent COVID-19 in Frontline Healthcare Workers. A Randomized Clinical Trial Miguel A Villasis-Keever , Mardia G López-Alarcón , Guadalupe Miranda-Novales , Jessie N Zurita-Cruz , Aly S Barrada-Vázquez , Joaquı́n González-Ibarra , Monserrat Martı́nez-Reyes , Concepción Grajales-Muñiz , Clara E Santacruz-Tinoco , Bernardo Martı́nez-Miguel , Jorge Maldonado-Hernández , Yazmı́n Cifuentes-González , Miguel Klünder-Klünder , Juan Garduño-Espinosa , Briseida López-Martı́nez , Israel Parra-Ortega PII: DOI: Reference: S0188-4409(22)00045-5 https://doi.org/10.1016/j.arcmed.2022.04.003 ARCMED 2733 To appear in: Archives of Medical Research Received date: Revised date: Accepted date: February 28, 2022 March 25, 2022 April 11, 2022 Please cite this article as: Miguel A Villasis-Keever , Mardia G López-Alarcón , Guadalupe Miranda-Novales , Jessie N Zurita-Cruz , Aly S Barrada-Vázquez , Joaquı́n González-Ibarra , Monserrat Martı́nez-Reyes , Concepción Grajales-Muñiz , Clara E Santacruz-Tinoco , Bernardo Martı́nez-Miguel , Jorge Maldonado-Hernández , Yazmı́n Cifuentes-González , Miguel Klünder-Klünder , Juan Garduño-Espinosa , Briseida López-Martı́nez , Israel Parra-Ortega , Efficacy and Safety of Vitamin D Supplementation to Prevent COVID-19 in Frontline Healthcare Workers. A Randomized Clinical Trial, Archives of Medical Research (2022), doi: https://doi.org/10.1016/j.arcmed.2022.04.003 This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2022 Published by Elsevier Inc. on behalf of Instituto Mexicano del Seguro Social (IMSS). Arch Med Res 22-00242 Highlights  Due to its immunomodulatory properties, vitamin D is expected to have a role in viral infections including SARS-CoV-2  Supplementation with vitamin D in highly exposed individuals such as frontline health care workers, decreases the susceptibility for SARS-CoV-2 infection  The preventive effect of vitamin D supplementation is independent of vitamin D status  Medium doses of vitamin D (4000 IU per day) seems safe for short periods of supplementation 1 Arch Med Res 22-00242 ORIGINAL ARTICLE Vitamin D effectiveness to Prevent COVID-19 Efficacy and Safety of Vitamin D Supplementation to Prevent COVID-19 in Frontline Healthcare Workers. A Randomized Clinical Trial Miguel A Villasis-Keevera, Mardia G López-Alarcónb, Guadalupe Miranda-Novalesa, Jessie N Zurita-Cruzc, Aly S Barrada-Vázquezb, Joaquín González-Ibarrad, Monserrat Martínez-Reyesb, Concepción Grajales-Muñize, Clara E Santacruz-Tinocoe, Bernardo Martínez-Miguele, Jorge Maldonado-Hernándezb, Yazmín Cifuentes-Gonzálezb, Miguel Klünder-Klünderf, Juan GarduñoEspinosaf, Briseida López-Martínezf, Israel Parra-Ortegaf a Unidad de Investigación en Análisis y Síntesis de la Evidencia, Centro Médico Nacional Siglo XXI, Instituto Mexicano del Seguro Social, Ciudad de México, México b Unidad de Investigación Médica..