Background Vitamin D is important for maintaining bone health but also appears to have immunomodulatory effects. Ankylosing spondylitis (AS) appears to be associated with reduced vitamin D.1 However it is not clear from previous studies in axial spondyloarthritis (axSpA) whether vitamin D deficiency is associated with increased disease activity and functional impairment. In AS the pathological process is that of inflammation and ossification with evidence for accelerated loss of bone mineral density. Vitamin D may therefore play a role in development and progression of disease. Season of assessment is important to adjust for as ultraviolet (UVB) generation of vitamin D varies throughout the year.
Objectives The aim of this study was to assess whether vitamin D deficiency is associated with disease activity and functional impairment in axSpA.
Methods Patients with axSpA, attending routine rheumatology clinics, had serum vitamin D (25OHD) concentrations measured along with disease activity (BASDAI), spinal pain VAS (VAS) and functional impairment (BASFI). Multivariate logistic regression models were used to assess association between 25OHD deficiency (<30nmol/L) and increasing tertiles of BASDAI, VAS and BASFI. Analyses were adjusted for age, gender, use of anti-TNF and season of testing.
Results 117 patients with axSpA (93% met New York classification criteria for AS) were assessed. The mean age was 48 years (SD13) and mean duration of symptoms 20 years (SD12). 75% were male and 37% were on anti-TNF. Median 25OHD was 50nmol/L [IQR34, 66] and 21 patients (18%) had vitamin D deficiency. Median BASDAI was 4.9 [IQR2.7, 7.8], VAS 4.0 [2.0, 8.0] and BASFI 5.7 [2.5, 8.0]. Association between vitamin D deficiency and tertiles of disease activity and function is shown in table 1. In the highest tertile of BASDAI there was a 4.6 fold increased odds of vitamin D deficiency, compared to the reference group. An 8.2 fold increase in vitamin D deficiency was observed in the highest VAS subgroup, compared to the reference group.
Conclusions Increasing disease activity but not functional impairment appear to be associated with vitamin D deficiency in this cross-sectional study of axSpA. This study support the hypothesis that vitamin D may have an immunomodulatory role in axSpA. However, vitamin D deficiency may contribute to non-specific musculoskeletal pain. Furthermore, deficiency may be a consequence of reduced engagement in activities with UVB exposure, although the lack of significant association with BASFI does not suggest this. Longitudinal studies are needed to explore causal association, as optimising vitamin D may be an adjunctive intervention to reduce disease activity in axSpA.
S Zhao et al. Systematic Review of Association between Vitamin D Levels and Susceptibility and Disease Activity of Ankylosing Spondylitis. Rheumatology 2014 (in press)
Disclosure of Interest None declared