Low Vitamin D Status and Its Association With Systemic Inflammation and Immune Dysregulation: A Retrospective...

Background and objective Vitamin D contributes to immune regulation and the control of inflammatory signaling. Deficient vitamin D status has been linked to greater systemic inflammatory activity, but its relationship with routinely used clinical markers such as erythrocyte sedimentation rate (ESR) and absolute eosinophil count (AEC) remains insufficiently characterized. The objective of this study is to assess whether low vitamin D status is associated with elevated ESR and eosinophilia in an internal medicine outpatient population. Methods This retrospective cross-sectional study included 200 patients evaluated at the Internal Medicine Clinic of Al-Ahli Hospital, Doha, Qatar, between January 1, 2022, and April 1, 2026. Participants were assigned to two equal groups according to serum 25-hydroxyvitamin D level: low vitamin D (n = 100) and normal (n = 100). For the purposes of this study, low vitamin D status was defined as serum 25-hydroxyvitamin D <30 ng/mL, combining deficiency and insufficiency categories, while normal vitamin D status was defined as 30-100 ng/mL. Elevated ESR was determined using age- and sex-specific thresholds, and eosinophilia was defined as an AEC >0.5 × 10⁹/L. Categorical comparisons were performed with Fisher's exact test. Results Vitamin D deficiency was associated with a higher prevalence of elevated ESR, identified in 23% of the low vitamin D group compared with 10% of the normal vitamin D group (relative risk (RR) 2.3; p = 0.021). Eosinophilia was also more frequent in the low vitamin D group, observed in 14% of patients versus 4% in those with normal vitamin D status (RR 3.5; p < 0.05). These findings demonstrate a significant association between low vitamin D levels and increased systemic inflammatory activity. Additionally, the higher prevalence of eosinophilia suggests a potential link between vitamin D deficiency and immune dysregulation. Conclusions Low vitamin D status was significantly associated with elevated ESR, supporting an association with systemic inflammatory activity. Eosinophilia was more frequent in the low vitamin D group, and this difference was statistically significant. Overall, these findings suggest that low vitamin D status may accompany broader inflammatory and immunologic imbalance.