Vitamin D3: Role in chronic inflammatory disorders.

Abstract

Background: Vitamin D3 (Calcitriol) plays a pivotal role in regulating immune function and mitigating chronic inflammation. Its immunomodulatory effects contribute to improved outcomes in autoimmune and inflammatory diseases such as rheumatoid arthritis, multiple sclerosis, polycystic ovarian syndrome, and inflammatory bowel disease.

Methods: This review synthesizes current evidence from 46 articles published between 2006 and 2025, from experimental, clinical, and randomized controlled trials examining the immunological effects, optimal dosing, and safety of Vitamin D3 supplementation in chronic inflammatory conditions.

Results: Vitamin D3 modulates both innate and adaptive immunity by enhancing antimicrobial peptide production and promoting mucosal integrity. It induces regulatory T cells while suppressing pro-inflammatory Th1 and Th17 subsets, decreasing levels of IL-6, TNF-α, IL-17, and IFN-γ and increasing IL-10 and TGF-β. Clinical studies demonstrate inverse associations between serum 25(OH)D levels and inflammatory markers such as high-sensitivity C-reactive protein (hsCRP) and neutrophil-to-lymphocyte ratio (NLR). Supplementation of 1000–4000 IU/day maintains optimal serum concentrations (30–60 ng/mL; 75–150 nmol/L), with the best anti-inflammatory effects observed near 36–40 ng/mL. Correcting deficiency (<25–30 nmol/L) yields the most significant clinical benefits, while benefits plateau beyond 75 nmol/L. Toxicity and hypercalcemia are rare below 100 ng/mL (250 nmol/L), and routine supplementation remains safe under medical supervision.

Conclusion: Maintaining serum 25(OH)D levels between 30–60 ng/mL through daily Vitamin D3 supplementation (1000–4000 IU) effectively reduces systemic inflammation and enhances immune regulation. This strategy represents a safe and beneficial adjunct in managing chronic inflammatory and autoimmune diseases.