Abstract: Journal of Endocrinological Investigation (2021) 44:2601–2607 https://doi.org/10.1007/s40618-021-01566-9 ORIGINAL ARTICLE Retrospective analysis of vitamin D status on ınflammatory markers and course of the disease in patients with COVID‑19 infection Y. A. Ünsal1 · Ö. Ö. Gül1 O. Ünsal3 · E. Ertürk1 · S. Cander1 · C. Ersoy1 · E. Aydemir1 · C. Ateş1 · Z. Uzun2 · E. Armağan2 · Received: 28 December 2020 / Accepted: 29 March 2021 / Published online: 5 April 2021 © Italian Society of Endocrinology (SIE) 2021 Abstract Purpose The aim of the study was to investigate the association between serum 25-hydroxyvitamin D status within the last 6 months prior to COVID-19 infection and parameters of immune function and clinical outcomes. Methods Fifty-six patients, who were admitted to the emergency clinic and diagnosed with COVID–19 infection, were included in the study. Data on clinical characteristics, inflammatory parameters and vitamin D status were recorded for each patient. All the participants had data on 25-hydroxyvitamin D status within the last 6 months prior to COVID-19 infection. Results The patients were stratified as those with vitamin D status less than 20 ng/mL and higher than 20 ng/mL. A group with vitamin D status less than 20 ng/mL had lower lymphocyte counts and lower haemoglobin levels that was statistically significant (respectively; p = 0.021, p = 0.035). Higher C-reactive protein (CRP) levels were seen in the vitamin D–deficient group (p = 0.013). It was observed that vitamin D status of the patients who required oxygen therapy were lower than those who did not require oxygen therapy, not statistically significant (p = 0.05). Patients who did not use vitamin D supplementation within 6 months prior to COVID-19 infection had more likely to be diagnosed with pneumonia (p = 0.004). Conclusion Cases with lower vitamin D status had increased inflammatory markers and worse clinical outcomes than patients with higher vitamin D status. This study suggests that vitamin D status can be used as a prognostic factor in COVID-19 patients, and vitamin D supplementation can be recommended to improve the clinical outcomes in COVID-19 infection. Keywords Vitamin D · COVID-19 · Immunity · Anti-inflammatory · Pneumonia E. Armağan earmagan9999@yahoo.com * Y. A. Ünsal yaseminunsalay@gmail.com Ö. Ö. Gül drozenoz@gmail.com O. Ünsal oktayunsal@uludag.edu.tr S. Cander drcander@gmail.com E. Ertürk erturkerdinc@gmail.com C. Ersoy ecanan@uludag.edu.tr 1 E. Aydemir ensaraydemir@gmail.com Faculty of Medicine, Department of Endocrinology and Diseases of Metabolism, Bursa Uludag University, Bursa, Turkey 2 C. Ateş drcsknates@gmail.com Faculty of Medicine, Emergency Department, Bursa Uludag University, Bursa, Turkey 3 Faculty of Medicine, Oncology Department, Ankara Gazi University, Ankara, Turkey Z. Uzun drziyauzun61@gmail.com 13 Vol.:(0123456789)