The Role of Vitamin D in Modulating the Innate Immune Response in Children with Vesicoureteral Reflux

Background: Vitamin D, through its role in antimicrobial peptide (AMP) expression, may influence innate immunity and inflammation in urinary tract infections (UTIs). This study evaluated its role in patients with vesicoureteral reflux (VUR) and its contribution to the pathophysiology of reflux nephropathy (RN). Methods: We conducted a cross-sectional observational study of 25 pediatric patients with VUR, representing a subgroup analysis of a larger cohort examined in a previous study. We determined patients' vitamin D status, correlated it with recurrent UTIs and RS, and explored its relationship with urinary LL-37, NGAL, and IL-6 levels as markers of innate immune function. Results: Serum vitamin D levels ranged from 10.7 to 123.2 ng/mL (mean 39.5 ng/mL); 12% had deficiency and 20% had insufficient levels. Low vitamin D levels were detected in patients with more than five acute pyelonephritis (APNs), with a mean value classified as insufficient (27.3 ng/mL). Patients with RS had a lower mean vitamin D level compared to those without (30.51 ng/mL vs. 41.23 ng/mL), though the difference was not statistically significant (p = 0.39). No significant associations were found between vitamin D and urinary IL-6 or NGAL levels. A strong positive correlation was observed between vitamin D and urinary LL-37/creatinine (r = 0.78, r² = 0.61). Conclusions: Vitamin D appears to influence the frequency of UTIs and the development of RS, primarily by modulating LL-37 secretion, suggesting a possible role in the pathophysiology of RN.