The Effect of Vitamin D Supplementation on Clinical and Laboratory Biomarkers in Patients with Rheumatoid Arthritis: A Systematic Review and Meta-Analysis of Randomised Controlled Trials.

Aim: Rheumatoid arthritis (RA) is recognised as an inflammatory condition. Evidence indicates that vitamin D modulates inflammation by influencing diverse immune cells. The purpose of this systematic review and meta-analysis was to assess the effectiveness of vitamin D as a supplement for RA in comparison to a control group. Methods: We searched PubMed, Embase, Scopus, and Web of Science databases through March 2025 using targeted search terms. Our inclusion criteria encompassed clinical studies that enrolled RA patients and compared vitamin D supplementation against either placebo or standard care protocols. The results from the chosen studies were reported as Standardised mean differences (SMD) using random effect model with a 95% confidence interval. Results: Vitamin D supplementation resulted in a significant improvement in the VAS [SMD = -1.54, 95% CI (-2.53, -0.55), P = 0.002], serum vitamin D level [SMD = 1.52, 95% CI (0.86, 2.17), P = 0.001] and CRP [SMD = -0.88, 95% CI (-1.31, -0.44), P =0.001] but not in other outcomes. There was considerable heterogeneity among the studies for VAS (I2 = 97.4%, P = 0.001), DAS28 (I2 = 89.1%, P = 0.001), serum vitamin D Levels (I2 = 94.7%, P = 0.001), CRP (I2 = 84.1%, P = 0.001), and ESR (I2 = 84.1%, P = 0.001). Conclusion: The intervention groups receiving vitamin D supplementation showed statistically significant improvements in serum vitamin D levels, visual analog scale VAS scores, and CRP levels compared to control groups among RA patients.