Unveiling the Clinical and Biochemical Impact of Vitamin D Deficiency in Indian Rheumatoid Arthritis Patients: A Cross-Sectional Analysis.

Background Rheumatoid arthritis (RA) is a chronic autoimmune disease characterized by persistent synovial inflammation, joint destruction, and systemic complications. Despite therapeutic advances, disease activity remains variable, and modifiable factors influencing severity are under investigation. Vitamin D, beyond its role in bone metabolism, exerts immunomodulatory effects and may influence RA pathogenesis. However, evidence regarding its association with disease activity remains inconsistent. This study aimed to evaluate the clinical and biochemical correlates of serum 25-hydroxyvitamin D (25(OH)D) levels in RA patients within an Indian cohort. Methodology A cross‑sectional study was conducted among 50 newly diagnosed, treatment‑naïve patients with RA, aged over 18 years, at a tertiary care center in India. Demographic details, tender and swollen joint counts, visual analog scale (VAS) scores, erythrocyte sedimentation rate (ESR), C‑reactive protein (CRP), and Disease Activity Score 28 (DAS‑28) were recorded, while serum 25(OH)D concentrations were measured and categorized as normal, insufficient, or deficient. Statistical analyses were performed using SPSS version 20, with descriptive statistics expressed as mean ± SD and interquartile ranges (IQRs). Group differences in serum 25(OH)D were assessed using one‑way analysis of variance, followed by Tukey's post hoc test. To determine the structural independent effects of circulating vitamin D levels on baseline RA severity, a multiple linear regression analysis was performed on the cohort. Receiver operating characteristic (ROC) curve analysis was conducted to determine sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and area under the curve (AUC) for ESR and DAS‑28 in predicting disease activity, with statistical significance set at p-values ≤0.05. Results Of the 50 patients tested, rheumatoid factor (RF) was positive in 46 (92.00%), while the remaining four patients were negative for RF but positive for anti‑cyclic citrullinated peptide (anti‑CCP) antibodies. The mean age was 40.32 ± 3.46 years (IQR = 35-46). The median tender joint count was 2.0 (IQR = 1-3), and the swollen joint count was 4.00 (IQR = 2.00-5.00). The mean DAS‑28 score was 4.11 ± 1.50 (IQR = 3.20-5.10), indicating predominantly moderate disease activity. Pain intensity assessed by VAS averaged 4.58 ± 1.88 (IQR = 3-6). ESR averaged 30.92 ± 18.89 mm/hour (IQR = 20-42), while CRP was 5.18 ± 4.65 mg/dL (IQR = 2.10-7.80). Serum 25(OH)D levels were relatively low, with a mean of 26.84 ± 3.96 ng/mL (IQR = 18.00-32.00), highlighting the prevalence of vitamin D deficiency in this population. The multiple linear regression model significantly predicted continuous DAS‑28 scores (F (3, 46) = 21.34, p < 0.001), explaining 58.2% of the variance (R² = 0.582). Serum 25(OH)D emerged as a highly significant and independent inverse determinant of baseline disease severity (B = -0.091, SE = 0.011, β = -0.741, p < 0.001). The area under the curve was 0.87 for ESR and 0.82 for serum 25(OH)D, underscoring good overall accuracy in predicting disease severity. Conclusions Vitamin D deficiency is a robust independent determinant of disease activity in Indian RA patients, underscoring the importance of monitoring vitamin D status alongside composite disease activity scores.