Association of Serum Vitamin D Level and Hematological Inflammatory Indices in Participants of the MASHAD Study

ABSTRACT Background and Aim Vitamin D, a fat‐soluble vitamin, has various vital roles in physiological processes. Recent evidence suggests that optimal vitamin D levels may be associated with improved immune function and reduced systemic inflammation. The present study aims to evaluate associations between serum vitamin D levels and various hematological inflammatory indices in participants of the MASHAD cohort study, Mashhad, Iran. Methods This study was designed as a cross‐sectional analysis conducted within the framework of phase I of the MASHAD cohort study. Participants (aged ≥ 18 years old and signed an informed consent) were recruited from a defined population, ensuring the representativeness of the sample for evaluation of potential association between serum vitamin D levels and hematological inflammatory indices including Red Cell Distribution Width (RDW‐CV), high‐sensitivity C‐reactive protein (hs‐CRP), systemic immune‐inflammation index (SII), platelet‐to‐lymphocyte ratio (PLR), Neutrophil‐to‐Lymphocyte Ratio (NLR), Mean Platelet Volume (MPV), and Platelet Distribution Width (PDW). Results A total of 458 participants were included in the current study, comprising 229 males and 229 females. Serum vitamin D had weak correlation with hs‐CRP ( r = −0.02), SII ( r = −0.01), PLR ( r = 0.05), NLR ( r = 0.01), PDW ( r = −0.05), and RDW‐CV ( r = −0.04). For males, no significant differences were observed in RDW‐CV, PDW, MPV, NLR, or PLR across the vitamin D quartiles ( p > 0.05 for all comparisons). In contrast, among female participants, significant differences in PDW ( p = 0.026) between quartile groups 1 and 4, and marginal significance between quartile 1 and 3 for RDW ( p = 0.062) were observed. Conclusion The current findings revealed a weak association between serum vitamin D concentrations and inflammatory indicators. Among hematological parameters, gender‐based differences were observed, with PDW and RDW levels significantly varying between vitamin D quartiles in women.