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