25-Hydroxyvitamin D and Complete Blood Count–Derived Inflammatory Indices in Children and Adolescents: Comparison of Obesity, Malnutrition, and Healthy Controls

AIM: To compare serum 25-hydroxyvitamin D [25(OH)D] levels and complete blood count (CBC)-derived inflammatory indices— neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), systemic immune-inflammation index (SII), and systemic inflammation response index (SIRI) among children and adolescents aged 2–17 years in obesity, malnutrition, and healthy control groups, and to evaluate associations between 25(OH)D and these indices.
MATRERIAL and METHOD: This retrospective, cross-sectional observational study used medical records of patients aged 2-17 years who attended the Pediatric Outpatient Clinic of Yalova Training and Research Hospital between 2023 and 2025, had no additional complaints, and had no clinical evidence of acute infection. Participants were classified by age- and sex-specific body mass index (BMI) percentiles as obese (≥95th percentile), malnourished (<5th percentile), or control (5th–85th percentile). NLR, PLR, SII, and SIRI were calculated from CBC parameters. Group comparisons were performed, and age- and sex-adjusted multivariable models (multinomial logistic regression and, in the obese subgroup, age- and sex-adjusted linear regression with log-transformed dependent variables) were applied. Sampling month/season was not available and therefore could not be modeled.
RESULTS: A total of 710 participants were included (control n=510, malnutrition n=93, obesity n=107). The obesity group had lower 25(OH)D levels and a higher prevalence of 25(OH)D deficiency. SIRI showed the clearest separation among groups. In multivariable analyses, higher SII and SIRI in the obesity group and higher SIRI in the malnutrition group remained significant compared with controls. In the obese subgroup, higher 25(OH)D was significantly associated with lower ln(PLR) (β=-0.0142; p<0.001) and lower ln(SII) (β=-0.0162; p=0.005), with borderline inverse associations for ln(SIRI) (p=0.054) and ln(NLR) (p=0.051).
CONCLUSION: Our study showed that inflammation markers were increased in obese and malnourished children, with SIRI being particularly distinctive, and that low 25(OH)D levels in obese individuals may be associated with increased inflammation.