Abstract: Since January 2020 Elsevier has created a COVID-19 resource centre with free information in English and Mandarin on the novel coronavirus COVID19. The COVID-19 resource centre is hosted on Elsevier Connect, the company's public news and information website. Elsevier hereby grants permission to make all its COVID-19-related research that is available on the COVID-19 resource centre - including this research content - immediately available in PubMed Central and other publicly funded repositories, such as the WHO COVID database with rights for unrestricted research re-use and analyses in any form or by any means with acknowledgement of the original source. These permissions are granted for free by Elsevier for as long as the COVID-19 resource centre remains active. Journal of Steroid Biochemistry and Molecular Biology 203 (2020) 105751 Contents lists available at ScienceDirect Journal of Steroid Biochemistry and Molecular Biology journal homepage: www.elsevier.com/locate/jsbmb “Effect of calcifediol treatment and best available therapy versus best available therapy on intensive care unit admission and mortality among patients hospitalized for COVID-19: A pilot randomized clinical study” Marta Entrenas Castillo a, Luis Manuel Entrenas Costa a, *, José Manuel Vaquero Barrios a, Juan Francisco Alcalá Díaz b, José López Miranda b, Roger Bouillon c, José Manuel Quesada Gomez d a UGC de Neumología, Instituto Maimónides de Investigación Biomédica de Córdoba 9 (IMIBIC). Hospital Universitario Reina Sofía, Universidad de Córdoba, Avda. Menéndez 10 Pidal s/n, 14004 11, Córdoba, Spain b Departamento de Medicina Interna. IMIBIC, CIBER de Fisiopatología de la Obesidad y la Nutrición. Hospital Universitario Reina Sofía, Universidad de Córdoba, Fundación Progreso y Salud. Avda. Menéndez Pidal s/n, 14004 14, Córdoba, Spain c Department of Chronic Diseases, Metabolism and Ageing, Laboratory of Clinical and Experimental Endocrinology, KU Leuven, Herestraat, ON1/902, 3000, Leuven, Belgium d IMIBIC. CIBER de Fragilidad y Envejecimiento Saludable. Hospital Universitario Reina Sofía, Universidad de Córdoba, Fundación Progreso y Salud. Avda. Menéndez Pidal s/n, 18 14004, Córdoba, Spain A R T I C L E I N F O A B S T R A C T Keywords: COVID-19 SARS-CoV-2 Vitamin D Vitamin D3 or cholecalciferol Calcifediol or 25-hydroxyvitamin D3 1α, 25(OH)2D or 1α, 25-dihydroxyvitamin D or calcitriol Acute respiratory distress syndrome (ARDS) Cytokine/Chemokine storm Renin-angiotensin system Hypercoagulability Hydroxychloroquine Chloroquine Covidiol Neutrophil activity Vitamin D endocrine system Cuboidal alveolar coating cells type II Cathelicidin peptide Defensins TLR co-receptor CD14 Vitamin D receptor Objective: The vitamin D endocrine system may have a variety of actions on cells and tissues involved in COVID19 progression especially by decreasing the Acute Respiratory Distress Syndrome. Calcifediol can rapidly in­ crease serum 25OHD concentration. We therefore evaluated the effect of calcifediol treatment, on Intensive Care Unit Admission and Mortality rate among Spanish patients hospitalized for COVID-19. Design: Parallel pilot randomized open label, double-masked clinical trial. Setting: University hospital setting (Reina Sofia University Hospital, Córdoba Spain.) Participants: 76 consecutive patients hospitalized with COVID-19 infection, clinical picture of acute respiratory infection, confirmed by a radiographic pattern of viral pneumonia..