The relationship between vitamin D and disease activity and functional health status in rheumatoid arthritis

We aimed to establish the relationship between serum vitamin D levels and disease activity and health status in rheumatoid arthritis. Sixty-five patients with RA fulfilling ACR criteria for the classification of rheumatoid arthritis and forty healthy controls were included in this study. Disease activity was assessed according to the Disease Activity Score including 28 joint counts. C-reactive protein (CRP, mg/dl) was determined by the nephelometric method. Erythrocyte sedimentation rate (ESR, mm/h) was determined by the Westergren method. Rheumatoid factor (RF, IU/ml) was also determined by the nephelometric method, and RF > 20 IU/ml was defined as positive. 25-OH Vitamin D EIA Kit was used to measure serum 25-OH Vitamin D levels. We found that the mean of the 25-OH D vitamin levels of the patients with RA was not different than that of controls (P = 0.936). We divided patients with RA into three groups according to DAS28 as low activity group (group 1, n = 25), moderate activity group (group 2, n = 25), and high activity group (group 3, n = 15). 25-OH vitamin D levels of the patients in the high activity group (group 3) were found to be the lowest (P < 0.001), and the patients with moderate disease activity had lower levels than those in the mild group (P = 0.033). Serum 25-OH vitamin D levels were significantly negatively correlated with DAS28, CRP, and HAQ (respectively, r = -0.431, P = 0.000, r = -0.276, P = 0.026, and r = -0.267, P = 0.031). Serum vitamin D levels in patients with RA were similar those in the healthy controls, while it significantly decreases in accordance with the disease activity and decreasing functional capacity.