Abstract: BRIEF RESEARCH REPORT published: 05 July 2022 doi: 10.3389/fnut.2022.934258 Vitamin D 25OH Deficiency and Mortality in Moderate to Severe COVID-19: A Multi-Center Prospective Observational Study Laura Bogliolo 1*† , Emanuele Cereda 2† , Catherine Klersy 3 , Ludovico De Stefano 1 , Federica Lobascio 2 , Sara Masi 2 , Silvia Crotti 2 , Serena Bugatti 1 , Carlomaurizio Montecucco 1 , Stefania Demontis 4 , Annalisa Mascheroni 5 , Nadia Cerutti 6 , Alberto Malesci 7 , Salvatore Corrao 8,9 , Riccardo Caccialanza 2† and the NUTRI-COVID19 Collaborative Working Group 9 1 Edited by: Kuo-Cheng Lu, Fu Jen Catholic University Hospital, Taiwan Reviewed by: Guoxun Chen, The University of Tennessee, United States Nasser M. Al-Daghri, King Saud University, Saudi Arabia *Correspondence: Laura Bogliolo l.bogliolo@smatteo.pv.it † These authors have contributed equally to this work Specialty section: This article was submitted to Clinical Nutrition, a section of the journal Frontiers in Nutrition Received: 02 May 2022 Accepted: 15 June 2022 Published: 05 July 2022 Citation: Bogliolo L, Cereda E, Klersy C, Stefano LD, Lobascio F, Masi S, Crotti S, Bugatti S, Montecucco C, Demontis S, Mascheroni A, Cerutti N, Malesci A, Corrao S, Caccialanza R and the NUTRI-COVID19 Collaborative Working Group (2022) Vitamin D 25OH Deficiency and Mortality in Moderate to Severe COVID-19: A Multi-Center Prospective Observational Study. Front. Nutr. 9:934258. doi: 10.3389/fnut.2022.934258 Frontiers in Nutrition | www.frontiersin.org Division of Rheumatology, Fondazione IRCCS Policlinico San Matteo, Pavia, Italy, 2 Clinical Nutrition and Dietetics Unit, Fondazione IRCCS Policlinico San Matteo, Pavia, Italy, 3 Clinical Epidemiology & Biostatistics Unit, Fondazione IRCCS Policlinico San Matteo, Pavia, Italy, 4 Nutritional Unit, Giovanni Borea Civil Hospital, Sanremo, Italy, 5 Clinical Nutrition and Dietetics Unit–ASST Melegnano e Martesana, Melegnano (Milano), Italy, 6 Medicine and Dietetics Unit, ASST Pavia, Pavia, Italy, 7 Division of Gastroenterology and Digestive Endoscopy, Department of Gastroenterology, Humanitas Research Hospital, Milano, Italy, 8 Department of Health Promotion Sciences, Maternal and Infant Care, Internal Medicine and Medical Specialties (PROMISE), University of Palermo, Palermo, Italy, 9 COVID Unit, Department of Internal Medicine, National Relevance and High Specialization Hospital Trust ARNAS Civico, Di Cristina, Benfratelli, Palermo, Italy Introduction: Several studies and meta-analyses suggested the role of vitamin D 25OH in preventing severe forms of coronavirus disease 2019 (COVID-19). However, the evidence on the clinical benefits of vitamin D 25OH adequacy in patients hospitalized for COVID-19 remain conflicting and speculative. We aimed to investigate the association between vitamin D 25OH serum levels and mortality in hospitalized patients with moderate to severe COVID-19. Method: This prospective observational multicentre study included 361 consecutive patients with moderate to severe COVID-19 admitted to the Italian hospitals involved in the NUTRI-COVID19 trial from March to August 2020. For each patient, serum vitamin D 25OH levels were assessed 48 h since admission and classified as deficient (<20 ng/mL) or adequate (≥20 ng/mL). We built a propensity score for low/adequate vitamin D 25OH levels to balance the clinical and demographic properties of the cohort, which resulted in 261 patients with good common support used for the survival..