Abstract: doi: 10.1210/jendso/bvab048 | Journal of the Endocrine Society | A279 aimed to determine whether vitamin D supplementation in vitamin D insufficient patients was associated with fewer severe COVID-19 outcomes, defined as mechanical ventilation or death. Methods: Retrospective study that analyzed data from all adult patients admitted to our tertiary care center between March 2020 and July 2020 with a positive RT-PCR for SARS CoV-2 and a serum 25-hydroxyvitamin D (25[OH]D) level measured within 90 days prior to the index admission. Patients with 25(OH)D <30 ng/mL were considered vitamin D insufficient and patients ordered for least one weekly dose of ≥1,000 units of ergocalciferol or cholecalciferol were considered supplemented. Supplemented vitamin D insufficient patients were compared to nonsupplemented vitamin D insufficient patients in terms of severe COVID-19 disease as defined by mechanical ventilation or death. Results: 129 COVID-19 patients with a vitamin D level <30 ng/mL were identified, with a median vitamin D level of 21.4 ng/mL. A total of 43 patients (33.3%) had severe COVID-19 outcomes. 65 (50.4%) patients with vitamin D insufficiency were supplemented and 64 (49.6%) were not supplemented. Vitamin D supplementation with ≥1,000 units (OR 0.6, 95% CI 0.28 - 1.40; p=0.25), ≥5,000 units (OR 0.5, 95% CI 0.26 - 1.23; p=0.15), or ≥50,000 units (OR 1.0, 95% CI 0.42–2.20, p=0.92) weekly had no statistically significant effect on severe COVID-19 outcomes. The odds of severe COVID-19 outcomes in supplemented patients were non-significantly reduced at lower cutoff values for vitamin D insufficiency (<20 ng/mL and <12 ng/ mL) for all supplementation amounts. Conclusion: Vitamin D supplementation in patients with vitamin D insufficiency did not significantly reduce severe COVID-19 outcomes; however, vitamin D supplementation was associated with non-statistically significant reduced odds of severe COVID19 outcomes at lower cutoff values of vitamin D level. These results demonstrate that Vitamin D supplementation may have a protective effect against severe COVID-19 outcomes in patients with lower baseline levels of vitamin D. Bone and Mineral Metabolism VITAMIN D, DIABETES AND ENERGY METABOLISM The Effect of Vitamin D Supplementation on Severe COVID-19 Outcomes in Patients With Vitamin D Insufficiency 1 Bone and Mineral Metabolism VITAMIN D, DIABETES AND ENERGY METABOLISM 2 Corinne Levitus, DO , Sweta Chekuri, MD , Andrei Assa, MD2, Laurel Mohrmann, MD2, Alexandra Zindman, MD3, Vafa Tabatabaie, MD1, Fabrizio Toscano, MD3, Masud Ahmed, PA-C2, Sarah W. Baron, MD2. 1 Albert Einstein College of Medicine and Montefiore Medical Center, Department of Internal Medicine, Division of Endocrinology, Bronx, NY, USA, 2Albert Einstein College of Medicine and Montefiore Medical Center, Department of Medicine, Division of Hospital Medicine, Bronx, NY, USA, 3Albert Einstein College of Medicine and Montefiore Medical Center, Department of Internal Medicine, Residency Training Program, Bronx, NY, USA. The Impact of Glucose Tolerance States on Bone Mineral Density and Fracture Rate Maria Chang Villacreses, MD1, panadeekarn panjawatanan, MD2, Rudruidee Karnchanasorn, MD3, Horng-Yih Ou, MD & PhD4, Wei Feng, MD5, Raynald Samoa, MD6, Lee-Ming Chuang, MD, PhD7, Ken C. Chiu, MD8. 1 CITY OF HOPE NATIONAL MEDICAL CENTER, Duarte, CA, USA, 2Bassett Medical Center, Cooperstown, NY, USA, 3The University of Kansas Medical Center, Kansas City, KS, USA, 4 National..