Hypovitaminosis D in Patients with Ankylosing Spondylitis: Frequency and Consequences

This study aimed to assess the frequency of hypovitaminosis D in patients with Ankylosing Spondylitis (AS) compared to healthy controls and evaluate its association with disease activity, structural damage and Bone Mineral Density (BMD).Serum 25(OH) D in 30 AS male patients was compared to 30 matched healthy controls. AS disease activity was assessed using AS Disease Activity Score and C - reactive protein (ASDAS- CRP). Bath AS Functional Index (BASFI) and Bath AS Metrology Index (BASMI) were used to assess the functional impairment and the spinal mobility, respectively. Radiological damage was scored according to modified Stoke AS Spine Score (mSASSS) and BMD was measured in the lumbar spine and femoral neck.The mean serum 25(OH)D levels in AS patients were significantly lower compared to healthy controls (27.73 ± 14.27 vs. 38.46 ± 8.11ng/ml, P <0.001). Among the patients, 60% exhibited hypovitaminosis D. AS patients with hypovitaminosis D had significantly higher ASDAS-CRP (p<0.001), BASFAI (p=0.0003) and mSASSS (p=0.04) scores. Additionally, BMD and Z scores at lumbar and femoral sites were significantly reduced in patients with hypovitaminosis D (P < 0.05). Serum 25(OH)D was positively correlated with BMD (lumbar and femoral; p=0.002 and p=0.01 respectively) and Z scores (lumbar and femoral; p<0.001and p=0.01 respectively), whereas, negatively correlated with ASDAS-CRP (p<0.001), BASFI (p<0.001), and mSASSS (p=0.003). ASDAS - CRP was the only significant predictor of hypovitaminosis D in AS patients.Hypovitaminosis D is prevalent among AS patients and is associated with increased risk of active disease, impaired function, radiographic severity and bone mineral loss. Future studies with a larger sample size are recommended to assess the impact of vitamin D deficiency on radiological progression in AS and to address whether or not vitamin D supplementation will help control the active disease.