Relevance of serum vitamin D level and the disease activity in rheumatoid arthritis

Rheumatoid arthritis (RA) is one of the most prevalent autoimmune diseases in the world. Some of the researches have suggested that the serum vitamin D level may relate to disease activity. The current study was designed to identify the correlation between serum vitamin D level and the disease activity index (DAI). In this sectional study, 108 patients (diagnosed based on the American Committee of Rheumatology criteria) were enrolled. In all cases after determining the serum vitamin D level and ESR, complete joint examination were done. The normal range of vitamin D was 47.7 - 144 nm/lit. Then, the specified disease activity form (DAS-28) and visual analog scales (VAS) were filled out. The correlation between disease activity index, (based on VAS, tendered or swelled joints and ESR) and serum vitamin D was analyzed using Chi square, Mann Whitney and t-tests. Seventy nine (73.14%) out of 108 patients had normal serum vitamin D and 29 (26.86%) had low serum vitamin D level. The mean age of patients with normal and low serum vitamin D level were 52.22±11.6 and 48.48±12.51, respectively (P=0.075). The mean DAI in normal and low vitamin D patients were 3.75±1.37 and 5.19±1.56, respectively (P=0.00). The mean number of swollen joints in normal and low vitamin D patients was 1.24±1.39 and 3.65±3.3, respectively (P=0.001). The mean number of tender joints in normal and low vitamin D patients were 6.84±4.41 and 9.44±3.62, respectively (P=0.042). The mean ESR in normal and low vitamin D patients were 19.40±12.40 and 37.91±21.72, respectively (P=0.002). Moreover, the mean VAS in normal and low vitamin D patients was 23.29±19.42 and 50.68±30.78, respectively (P=0.003). The more active the RA, the less serum vitamin D level.