Serum Vitamin D Levels at Birth and Late-Onset Neonatal Sepsis in Preterm Neonates: A Retrospective Exploratory...

Background: Late-onset neonatal sepsis (LONS) remains a major cause of morbidity in preterm neonates admitted to the neonatal intensive care unit (NICU), yet the contribution of vitamin D status to neonatal infectious susceptibility remains uncertain. Objective: To evaluate clinical and demographic variables and serum vitamin D levels assessed at birth in preterm neonates with and without LONS. Methods: A retrospective observational cohort study was conducted in a tertiary NICU in northeastern Mexico between May 2023 and October 2024. Preterm neonates (<37 weeks of gestation) with serum 25(OH)D measured within the first hour of life were included. Vitamin D status was classified as sufficient (≥30 ng/mL), insufficient (20-29 ng/mL), or deficient (<20 ng/mL). LONS was defined as sepsis occurring after 72 h of life. Comparisons between neonates with and without LONS were performed using Fisher's exact test for categorical variables and Student's t-test or Mann-Whitney U test for continuous variables, as appropriate. Results: Twenty-nine preterm neonates were included (mean gestational age: 32.0 ± 2.6 weeks; mean birth weight: 1748 ± 545 g). The mean serum 25(OH)D level at birth was 35.5 ± 13.0 ng/mL. LONS occurred in 31% (9/29) of neonates, of which 55% were microbiologically confirmed. No significant differences were observed in vitamin D levels between neonates with and without LONS (35.0 ± 12.0 vs. 35.7 ± 13.7 ng/mL; p = 0.899). Vitamin D deficiency was not associated with LONS (OR 1.13, 95% CI 0.09-14.28). The prevalence of vitamin D deficiency was low (10%) in this cohort. Conclusions: A clear association between serum 25(OH)D levels at birth and the development of LONS could not be demonstrated in this small exploratory cohort. Given the limited sample size and low prevalence of vitamin D deficiency, further multicenter prospective studies are required to better understand the potential relationship between vitamin D status and neonatal infectious outcomes.