Objective:
Vitamin D plays an important role in mineral turnover and bone remodeling and there are increasing data about its immunomodulatory potential in different rheumatologic disorders. Deficiency of vitamin D is frequent in patients with spondyloarthritis (SpA) and some data suggest its association with increased disease activity and structural damage. However, its exact role in the pathogenesis of SpA and its association with disease activity are still a matter of debate.

Material and methods:
A cross-sectional study of patients diagnosed with axial spondyloarthritis (axSpA) and peripheral spondyloarthritis (perSpA) according to Assessment of Spondyloarthritis International Society classification criteria was performed. The correlation between concentration of 25-hydroxyvitamin D – 25(OH)D – and disease activity scores (Bath Ankylosing Spondylitis Disease Activity Index – BASDAI, Ankylosing Spondylitis Disease Activity Score – ASDAS), inflammatory markers (C-reactive protein – CRP, erythrocyte sedimentation rate – ESR) and clinical symptoms (arthritis, enthesitis, dactylitis) was performed.

Results:
We included 40 patients with axSpA and 23 patients with perSpA. The mean concentration of 25(OH)D was 24.9 ng/ml (SD 12.49). Forty-seven (74.6%) patients had 25(OH)D below the recommended threshold (< 30 ng/ml). We found no statistically significant negative correlation between the level of 25(OH)D and disease activity of axSpA and perSpA in terms of clinical symptoms (arthritis, enthesitis, dactylitis), inflammatory markers (ESR, CRP) and disease activity scores (BASDAI, ASDAS). These results did not change after adjustment for supplementation of vitamin D and seasonal variation.

Conclusions:
Our data show no correlation between the concentration of 25(OH)D in the serum and disease activity in two subgroups of SpA. However, this does not exclude the potential role of vitamin D in pathogenesis of SpA. Further studies are required to evaluate the optimal range of 25(OH)D serum concentration in axSpA and perSpA patients with its possible immunomodulatory potential and influence on disease activity.