Exploring the Association of Vitamin D and VDR Polymorphisms with Disease Severity in COVID-19 and Influenza

<b>Background</b>: Respiratory viral infections such as COVID-19 and influenza represent significant public health threats, especially in vulnerable populations. Vitamin D has been promoted as an immunomodulatory agent, with previous studies suggesting an association between vitamin D levels and disease severity in respiratory infections. Additionally, genetic variations in the vitamin D receptor (VDR) may influence immune responses. <b>Methods</b>: This study investigates the relationship between vitamin D levels, VDR polymorphisms (rs1544410, rs731236, and rs7975232), and clinical severity in hospitalized patients with COVID-19 and influenza during the 2023-2024 winter season. <b>Results</b>: A total of 71 patients were included in this cross-sectional study. Vitamin D levels were significantly lower in severe COVID-19 cases (8.08 ng/mL, IQR: 4.79-15.7) compared to moderate forms (32.6 ng/mL, IQR: 13.0-38.6), as well as severe influenza cases (25.6 ng/mL, IQR: 18.9-34.5). Additionally, severe COVID-19 patients exhibited higher inflammatory markers (CRP, neutrophil count) and lower lymphocyte counts. However, no significant association was found between VDR polymorphisms and disease severity or vitamin D levels. <b>Conclusions</b>: These findings highlight the potential role of vitamin D in modulating disease severity in respiratory viral infections, while the influence of genetic polymorphisms remains uncertain. Further research is needed to determine whether vitamin D supplementation could improve clinical outcomes in these infections.