Abstract: SYSTEMATIC REVIEW published: 22 December 2021 doi: 10.3389/fpubh.2021.736665 Vitamin D Status and SARS-CoV-2 Infection and COVID-19 Clinical Outcomes Iacopo Chiodini 1,2*† , Davide Gatti 3† , Davide Soranna 4 , Daniela Merlotti 5 , Christian Mingiano 5 , Angelo Fassio 3 , Giovanni Adami 3 , Alberto Falchetti 6 , Cristina Eller-Vainicher 7 , Maurizio Rossini 3 , Luca Persani 1,2 , Antonella Zambon 4,8 and Luigi Gennari 5 1 Department of Endocrine and Metabolic Diseases, Istituto di Ricovero e Cura a Caratttere Scientifico (IRCCS), Istituto Auxologico Italiano, Milan, Italy, 2 Department of Medical Biotechnology and Translational Medicine, University of Milan, Milan, Italy, 3 Rheumatology Unit, University of Verona, Verona, Italy, 4 Biostatistic Unit, Istituto di Ricovero e Cura a Caratttere Scientifico (IRCCS), Istituto Auxologico Italiano, Milan, Italy, 5 Department of Medicine, Surgery and Neurosciences, University of Siena, Siena, Italy, 6 Unit of Rehabilitation Medicine, San Giuseppe Hospital, Istituto di Ricovero e Cura a Caratttere Scientifico (IRCCS), Istituto Auxologico Italiano, Piancavallo, Italy, 7 Unit of Endocrinology, Fondazione Istituto di Ricovero e Cura a Caratttere Scientifico (IRCCS) Cà Granda, Milan, Italy, 8 Department of Statistics and Quantitative Methods, Università di Milano-Bicocca, Milan, Italy Edited by: Yoav Keynan, University of Manitoba, Canada Reviewed by: Naveen Kumar Devanga Ragupathi, The University of Sheffield, United Kingdom William B. Grant, Sunlight Nutrition and Health Research Center, United States *Correspondence: Iacopo Chiodini iacopo.chiodini@unimi.it † These authors have contributed equally to this work Specialty section: This article was submitted to Infectious Diseases - Surveillance, Prevention and Treatment, a section of the journal Frontiers in Public Health Received: 27 July 2021 Accepted: 11 November 2021 Published: 22 December 2021 Citation: Chiodini I, Gatti D, Soranna D, Merlotti D, Mingiano C, Fassio A, Adami G, Falchetti A, Eller-Vainicher C, Rossini M, Persani L, Zambon A and Gennari L (2021) Vitamin D Status and SARS-CoV-2 Infection and COVID-19 Clinical Outcomes. Front. Public Health 9:736665. doi: 10.3389/fpubh.2021.736665 Background: Several studies suggest an association between serum 25-hydroxyvitamin D (25OHD) and the outcomes of Severe Acute Respiratory Syndrome Corona-Virus-2 (SARS-CoV-2) infection, in particular Coronavirus Disease-2019 (COVID-19) related severity and mortality. The aim of the present meta-analysis was to investigate whether vitamin D status is associated with the COVID-19 severity, defined as ARDS requiring admission to intensive care unit (ICU) or mortality (primary endpoints) and with the susceptibility to SARS-CoV-2 and COVID-19-related hospitalization (secondary endpoints). Methods: A search in PubMed, ScienceDirect, Web of Science, Google Scholar, Scopus, and preprints repositories was performed until March 31th 2021 to identify all original observational studies reporting association measures, or enough data to calculate them, between Vitamin D status (insufficiency <75, deficiency <50, or severe deficiency <25 nmol/L) and risk of SARS-CoV-2 infection, COVID-19 hospitalization, ICU admission, or death during COVID-19 hospitalization. Findings: Fifty-four studies (49 as fully-printed and 5 as pre-print publications) were included for a total of 1,403,715 individuals. The association between vitamin D status and SARS-CoV2 infection, COVID-19..