Abstract: Clinical Nutrition xxx (xxxx) xxx Contents lists available at ScienceDirect Clinical Nutrition journal homepage: http://www.elsevier.com/locate/clnu Covid-19 Vitamin D deficiency in critically ill COVID-19 ARDS patients Quirin Notz a, *, Johannes Herrmann a, Tobias Schlesinger a, Peter Kranke a, Magdalena Sitter a, Philipp Helmer a, Jan Stumpner a, Daniel Roeder a, Karin Amrein b, Christian Stoppe a, Christopher Lotz a, Patrick Meybohm a a b Department of Anesthesiology and Intensive Care Medicine, University Hospital Wuerzburg, Germany Division of Endocrinology and Diabetology, Medical University of Graz, Austria a r t i c l e i n f o s u m m a r y Article history: Received 15 December 2020 Accepted 1 March 2021 Background & aims: Vitamin D's pleiotropic effects include immune modulation, and its supplementation has been shown to prevent respiratory tract infections. The effectivity of vitamin D as a therapeutic intervention in critical illness remains less defined. The current study analyzed clinical and immunologic effects of vitamin D levels in patients suffering from coronavirus disease 2019 (COVID-19) induced acute respiratory distress syndrome (ARDS). Methods: This was a single-center retrospective study in patients receiving intensive care with a confirmed SARS-CoV-2 infection and COVID-19 ARDS. 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D serum levels, pro- and anti-inflammatory cytokines and immune cell subsets were measured on admission as well as after 10e15 days. Clinical parameters were extracted from the patient data management system. Standard operating procedures included the daily administration of vitamin D3 via enteral feeding. Results: A total of 39 patients with COVID-19 ARDS were eligible, of which 26 were included in this study as data on vitamin D status was available. 96% suffered from severe COVID-19 ARDS. All patients without prior vitamin D supplementation (n ¼ 22) had deficient serum levels of 25-hydroxyvitamin D. Vitamin D supplementation resulted in higher serum levels of 25-hydroxyvitamin D but not did not increase 1,25dihydroxyvitamin D levels after 10e15 days. Clinical parameters did not differ between patients with sufficient or deficient levels of 25-hydroxyvitamin D. Only circulating plasmablasts were higher in patients with 25-hydroxyvitamin D levels 30 ng/ml (p ¼ 0.029). Patients with 1,25-dihydroxyvitamin D levels below 20 pg/ml required longer mechanical ventilation (p ¼ 0.045) and had a worse acute physiology and chronic health evaluation (APACHE) II score (p ¼ 0.048). Conclusion: The vast majority of COVID-19 ARDS patients had vitamin D deficiency. 25-hydroxyvitamin D status was not related to changes in clinical course, whereas low levels of 1,25-dihydroxyvitamin D were associated with prolonged mechanical ventilation and a worse APACHE II score. © 2021 Elsevier Ltd and European Society for Clinical Nutrition and Metabolism. All rights reserved. Keywords: Acute respiratory distress syndrome Vitamin D Critical care Nutrient supplementation Immune response