Is Serum 25-Hydroxyvitamin D Level Associated with Severity of COVID-19? A Retrospective Study.

(1) Background: SARS-COV2 infection has a clinical spectrum ranging from asymptomatic infection to COVID-19 with acute respiratory distress syndrome (ARDS). Although vitamin D deficiency is often found in patients with ARDS, its role in COVID-19 is not clear. The aim of this study was to explore a possible association between serum 25-hydroxyvitamin D levels and the severity of COVID-19 in hospitalised patients. (2) Methods: In this retrospective observational study, we analysed data from 763 patients hospitalised for COVID-19 in 2020 and 2021. Patients were included in the study if serum 25-hydroxyvitamin D was assessed 30 days before or after hospital admission. Vitamin D deficiency was defined as <50 nmol/L (<20 ng/mL). The primary outcome was COVID-19 severity. (3) Results: The overall median serum 25-hydroxyvitamin D level was 54 nmol/L (IQR 35-76); 47% of the patients were vitamin D deficient. Most patients had mild to moderate COVID-19 and no differences were observed between vitamin D deficient and non-deficient patients (81% vs. 84% of patients, respectively p = 0.829). (4) Conclusion: No association was found between serum 25-hydroxyvitamin D levels and COVID-19 severity in this large observational study conducted over 2 years of the pandemic.