Correspondence of vitamin D status with functional scores and disease activity among Croatian patients with ankylosing spondylitis: a preliminary study.

Background: Ankylosing spondylitis (AS) is a chronic inflammatory rheumatic disease which primarily affects the axial spine and sacroiliac joints. Over the past several years Vitamin D has been recognized as a hormone with significant immunomodulatory effect due to the fact that it inhibits T-cell proliferation and decreases the production of interleukin-2, interferon-γ, and tumor necrosis factor-α. Therefore, vitamin D may play a role in the development and progression of inflammatory diseases. Our aim was to estimate and evaluate the correspondence of vitamin D status with functional scores, spinal mobility and disease activity among patients with AS in Croatia.

Subjects And Methods: One hundred and fifty (150) AS patients were prospectively enrolled and assessed for disease activity, spinal mobility and functional disability. Blood samples were obtained from all patients and 25(OH)D concentration and inflammatory markers were determined. All patients underwent bone mineral density measurement at the lumbar spine (L1-L4) and proximal femur (total hip and femoral neck) with dual-energy x-ray absorptiometry.

Results: The prevalence of 25(OH)D inadequacy considering cut-offs of 75, 50 and 30 nmol/L was 80, 46.7 and 16.7% respectively. The mean 25(OH)D serum concentration was 52.63±23.45 nmol/L. There was no significant difference in mean 25(OH)D concentration regarding patient's age, sex, smoking status, season change, disease activity, spinal mobility or functional scores. However, there was a trend towards lower 25(OH)D concentration in patients with higher disease activity, worse spinal mobility and worse functional scores.

Conclusion: Our results showed that there is no significant association between serum 25(OH)D concentration and activity of AS. Given that significant proportion of our patients had inadequate vitamin D status, the role of vitamin D in pathophysiology of AS still remains to be elucidated.