Decreased Plasma Vitamin D Levels in Patients with Undifferentiated Spondyloarthritis and Ankylosing Spondylitis

Objective The aim of the present study was to evaluate the plasma vitamin D (vit D) levels and their association with the disease activity in patients with ankylosing spondylitis (AS) and undifferentiated spondyloarthritis (uSpA) compared with healthy populations. Methods This study included 161 spondyloarthritis patients (113 uSpA patients and 48 AS patients) attending our rheumatology out-patient clinic, along with 92 controls. Results The plasma vit D levels were 18 μg/L (8-38) in the AS group, 20 μg/L (4-92.3) in the uSpA group and 24.3 μg/L (7.2-76.8) in the control group. The plasma vit D levels of the AS patients were significantly lower than those of the patients in the control group (p=0.004). The men in the AS group had significanly lower vit D levels than those in the control group (p=0.005). On the other hand, the women in the uSpA group had significanly lower vit D levels than those in the control group (p=0.011). The vit D levels were inversely related to both erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) in the AS patients (p=0.002, R=-0.428; p