Evaluation of vitamin D as a negative acute phase reactant in rheumatoid arthritis

Objective: Rheumatoid Arthritis (RA) is a chronic, inflammatory, autoimmune disease characterized by symmetric polyarthritis, involving various tissues and organs. Besides its role in bone remodeling, vitamin D possesses numerous immunoregulatory properties. There are studies indicating a decrease in vitamin D levels during acute inflammatory conditions. Our study aimed to investigate whether 25-hydroxyvitamin D (25(OH)D) could be considered a negative acute phase reactant, with levels decreasing in the presence of inflammation. Materials and Methods: From January 2014 to December 2023, 90 patients diagnosed with rheumatoid arthritis who presented to the Manisa Celal Bayar University Medical Faculty, Department of Internal Medicine Rheumatology Clinic, were retrospectively examined. Patients under 18, those with additional diseases causing elevation in CRP and ESR, pregnant women, and those who had started vitamin D supplementation in the last three months were excluded from the study. Parameters compared included 25(OH)D, CRP, ESR, DAS-28, hemogram parameters, creatinine, albumin, AST, and ALT values at the time of initial presentation during active disease and 3-6 months after new treatment or treatment modification. The correlation between changes in 25(OH)D and other parameters was also investigated. Findings: The study included 79 female (87.8%) and 11 male (12.2%) patients diagnosed with RA, totaling 90 patients, presenting to the clinic between January 2014 and December 2023. The age of these patients ranged from 38 to 71, with an average age of 55.24 ± 10.15. From the initial visit to the second check-up 3-6 months later, statistically significant decreases were observed in DAS-28 (p=0.001), ESR (p=0.001), CRP (p=0.001), leukocytes (p=0.002), neutrophils (p=0.001), and platelets (p=0.002), while significant increases were noted in 25(OH)D (p=0.001) and albumin (p=0.005). No statistically significant correlation was found between the change in 25(OH)D and the changes in other parameters. Conclusion: Plasma 25(OH)D concentrations may decrease following inflammatory damage. Therefore, vitamin D levels may not be a reliable measure in acute inflammatory conditions. The appropriate assessment of vitamin D supplementation is necessary in autoimmune rheumatic diseases in the presence of inflammation. Keywords: Rheumatoid Arthritis, Vitamin D, Inflammatory parameters