Abstract: Endocrine (2021) 71:267–269 https://doi.org/10.1007/s12020-020-02597-7 RESEARCH LETTER Patients hospitalized with COVID-19 have low levels of 25-hydroxyvitamin D Nicholas Hutchings 1,2 Varta Babalyan2 Sisak Baghdasaryan2 Mushegh Qefoyan2 Narina Sargsyants3 Elena Aghajanova4 Anna Martirosyan5 Ruzanna Harutyunyan5 Olga Lesnyak6 Anna Maria Formenti7 Andrea Giustina7 John P. Bilezikian2,8 ● ● ● ● ● ● ● ● ● ● ● 1234567890();,: 1234567890();,: Received: 24 November 2020 / Accepted: 17 December 2020 / Published online: 16 January 2021 © The Author(s), under exclusive licence to Springer Science+Business Media, LLC part of Springer Nature 2021 The coronavirus (SARS-CoV-2) causes COVID-19. The disease has already afflicted over 54 million persons worldwide and has caused over 1.3 million deaths [1]. While most patients recovery uneventfully, some develop an acute pulmonary syndrome that requires hospitalization for supportive care [2]. Risk factors for symptomatic manifestations include male sex, diabetes mellitus, obesity, and hypertension [3, 4]. Another recently recognized potential risk factor is vitamin D deficiency. Vitamin D is an important modulator of innate and acquired immunity [5, 6]. Low levels are associated with bacterial and viral infections [7]. In addition, in countries with lower mean levels of 25-hydroxyvitamin D, mortality from COVID-19 is higher [8]. Preliminary studies suggest that vitamin D supplementation may improve outcomes [9]. While much of the data implicating vitamin D and COVID-19 has been indirect, recent reports have shown markedly reduced levels of 25-hydroxyvitamin D among those hospitalized with COVID-19 [10, 11]. These observations are consistent with * Nicholas Hutchings nicholas.hutchings@uci.edu 1 School of Medicine, University of California, Irvine, CA, USA 2 Osteoporosis Center of Armenia, Yerevan, Armenia 3 Ministry of Health, Yerevan, Armenia 4 Muratsan University Hospital, Yerevan, Armenia 5 Saint Gregory the Illuminator Medical Center, Yerevan, Armenia 6 North West State Medical University named after I.I. Mechnikov, Saint Petersburg, Russia 7 Institute of Endocrine and Metabolic Sciences, San Raffaele, Vita-Salute University and IRCCS Hospital, Milano, Italy 8 Endocrinology Division, Department of Medicine, New YorkPresbyterian Hospital / Columbia University Irving Medical Center, New York, NY, USA a plausible pathophysiological role of vitamin D in the disease process [6]. With an ethnically and culturally homogeneous population of approximately 3 million [12], Armenia has seen ~116,000 cases and 1700 deaths as of November 2020 [13]. At the Saint Gregory the Illuminator Medical Center (SGIMC) in Yerevan, a designated COVID-19 treatment hospital, we measured levels of 25-hydroxyvitamin D. We compared these levels with values that we have recently characterized in the free-living, healthy population of Armenia [14]. Methods Blood samples for measurement of 25-hydroxyvitamin D (ElectroChemiLuminescence immunoassay: Cobas e 411 autoanalyzer- Roche; Basel, Switzerland) were obtained from 330 consecutive hospitalized patients. We also recorded age, gender, height, weight, occupation, chronic conditions, prior tuberculosis infection, smoking status, use of supplemental oxygen, intubation status, duration of hospitalization until discharge, or death. Results Samples were collected over 5 weeks in summer, 2020. The most common comorbidities were hypertension,..