Background: Rheumatoid arthritis (RA) is a chronic autoimmune disease characterized by inflammation, joint destruction, and immune dysregulation. Vitamin D, a key regulator of the immune system, has been implicated in various autoimmune diseases, including RA. However, the exact role of vitamin D in immune modulation and its potential relationship with immune markers in RA patients remains underexplored. Objective: This study aimed to investigate the relationship between vitamin D deficiency and immune dysregulation in RA patients, with a focus on inflammatory markers, cytokines, and regulatory T-cells. Methodology: A cross-sectional study was conducted from 1st January to 30th August 2024, including 100 RA patients (50 males, 50 females) and 50 control participants (25 males, 25 females). Blood samples were collected from all participants to measure serum vitamin D levels, inflammatory markers (C-reactive protein [CRP], erythrocyte sedimentation rate [ESR]), and immune parameters (IL-10, IL-17, and regulatory T-cells). Data were analyzed using correlation analysis to examine relationships between vitamin D levels and immune parameters. Results: RA sufferers exhibited drastically decrease nutrition D degrees as compared to controls (18.5 ± 6.2 ng/mL vs. 32.1 ± 7.8 ng/mL, p < 0.001). Additionally, better inflammatory markers had been determined in RA patients, with CRP and ESR levels considerably expanded compared to controls (p < 0.001). A widespread high-quality correlation turned into found among vitamin D stages and IL-10 (r = 0.582, p < 0.001) and regulatory T-cells (r = 0.421, p < 0.001), whilst an inverse correlation changed into determined with IL-17 (r = -0.645, p < 0.001). Moreover, a terrible correlation between vitamin D stages and ESR (r = -0.512, p < 0.001) become additionally cited, suggesting a link between nutrition D deficiency and systemic irritation in RA. Conclusion: The outcomes of this observe assist the position of diet D in immune modulation and irritation in RA patients. Vitamin D deficiency turned into associated with better inflammatory markers and adjusted immune responses, together with accelerated levels of seasoned-inflammatory cytokines (IL-17) and reduced regulatory T-cellular characteristic. These findings highlight the potential therapeutic function of vitamin D supplementation in managing immune dysregulation and infection in RA. Further studies are had to affirm these outcomes and discover the medical benefits of diet D in RA remedy.