Correlation between Neonatal Hyperbilirubinemia and Serum 25-Hydroxyvitamin D

Background: Neonatal hyperbilirubinemia is a leading cause of hospital readmission, yet nearly half of the cases have an unknown etiology. Emerging evidence suggests that vitamin D deficiency, a globally prevalent condition, may be a significant modifiable risk factor for this common neonatal issue. Objective: This study aimed to determine the correlation between serum 25-hydroxyvitamin D [25(OH)D] and total serum bilirubin (TSB) levels in a of Iraqi neonates. Methods: This case control study was conducted at Al-Diwaniyah Maternity and Children Teaching Hospital in Iraq. Data and samples were collected over a four-month period between April 1, 2025, and July 31, 2025. A convenience sample of 75 term neonates was recruited, consisting of 50 infants diagnosed with hyperbilirubinemia (cases) and 25 healthy infants (controls). Serum TSB was quantified using colorimetric method and 25(OH)D levels were measured by immune assay. Results: The hyperbilirubinemia group had significantly lower mean vitamin D levels (9.51 ng/ml) compared to the control group (24.65 ng/ml; p<0.001), representing a 61.4% reduction. Conversely, mean TSB was substantially higher in cases (10.35 mg/dL) than in controls (2.70 mg/dL; p<0.001). A moderate, statistically significant negative correlation was identified between 25(OH)D and TSB levels (r = -0.441, p < 0.037). This indicates that lower vitamin D levels are directly associated with higher bilirubin levels across the entire study population. Conclusion: Vitamin D deficiency is a significant risk factor associated with the development of neonatal hyperbilirubinemia in this cohort of Iraqi neonates.