Correlation of Plasma 25D[sub.3] and Vitamin D Binding Protein Levels with COVID-19 Severity and Outcome in Hospitalized Patients

Background: The Coronavirus Disease-19 (COVID-19) caused by the Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) has been declared a worldwide pandemic. The severity of COVID-19 varies greatly across infected individuals. Possible factors may include plasma levels of 25(OH)D and vitamin D binding protein (DBP), as both are involved in the host immune response. Other possible nutrition-related factors include malnutrition and/or obesity which disrupt the optimal host immune response to infections. Current literature shows inconsistent evidence about the association of plasma 25(OH)D[sub.3] and DBP on infection severity and clinical outcomes. Objectives: This study aimed to measure plasma 25(OH)D[sub.3] and DBP in hospitalized COVID-19 cases and assess their correlation with infection severity, inflammatory markers, and clinical outcome. Methods: 167 patients were included in this analytical cross-sectional study, of which 81 were critical and 86 were non-critical hospitalized COVID-19 patients. Plasma levels of 25(OH)D[sub.3] , DBP, and the inflammatory cytokines, IL-6, IL-8, IL-10, and TNF-α were assessed using the Enzyme-linked Immunosorbent Assay (ELISA). Information regarding biochemical and anthropometrical indices, hospital length of stay (LoS), and illness outcome was obtained from the medical records. Results: Plasma 25(OH)D[sub.3] level was found to be significantly lower in critical compared to non-critical patients (Median = 8.38 (IQR = 2.33) vs. 9.83 (IQR = 3.03) nmol/L, respectively; p < 0.001), and it positively correlated with hospital LoS. However, plasma 25(OH)D[sub.3] did not correlate with mortality or any of the inflammatory markers. DBP on the other hand correlated positively with mortality (r[sub.s] = 0.188, p = 0.015) and hospital LoS (r[sub.s] = 0.233, p = 0.002). DBP was significantly higher in critical than non-critical patients (Median = 1262.18 (IQR = 463.66) vs. 1153.35 (IQR = 418.46) ng/mL, respectively; p < 0.001). Furthermore, IL-6 and IL-8 were significantly higher in critical than non-critical patients. However, no differences were found in IL-10, TNF-α, IL-10/TNF-α, TNF-α/IL-10, IL-6/IL-10, or CRP between groups. Conclusion: The current study found that critical COVID-19 patients had lower 25(OH)D[sub.3] than non-critical patients, yet, levels were found to be suboptimal in both groups. Further, critical patients had higher DBP levels as compared to non-critical patients. This finding may encourage future resea