Abstract
Background
Rheumatoid arthritis (RA) is the commonest chronic inflammatory arthritis, predominantly affecting small/medium joints and associated with extra-articular features. Previous studies have linked RA risk and disease activity with vitamin D-deficiency, but a causal role for vitamin D in RA is still unclear, partly due to heterogeneous study methods and sample populations. Moreover, no studies have focused specifically on vitamin D status (serum levels of 25-hydroxyvitamin D, 25OHD) in early RA, or whether low 25OHD is linked to progression from undifferentiated inflammatory arthritis to RA. Our objectives were therefore (1) to analyse serum 25OHD in early inflammatory arthritis, (2) to compare 25OHD levels with disease activity and fatigue in early RA and (3) to determine whether low serum 25OHD is associated with progression to RA.
Methods
We analysed 791 patients enrolled in the Birmingham Early Arthritis Cohort from 2013-19 at Sandwell and West Birmingham Hospitals NHS Trust and University Hospitals Birmingham NHS Trust. We collect baseline demographic data, serum 25OHD (ng/ml), and clinical variables including: duration of symptoms, duration of early morning stiffness (EMS), CRP, ESR, anti-CCP antibody status, Rheumatoid factor status, tender and swollen joint counts, DAS28-ESR, DAS28-CRP, Visual Analogue Scale (VAS) pain/fatigue and FACIT scores. Diagnosis was recorded at 0 and 12 months onwards as either RA, psoriatic arthritis (PsA), Undifferentiated Inflammatory Arthritis (UIA; synovitis not meeting other classification/diagnostic criteria), Clinical Suspect Arthralgia (CSA; arthralgia of an inflammatory type without synovitis), or Other. Data were analysed using SPSSv25. Full ethical approval was given for the study (REC12/WM/0258).
Results
Baseline demographic data were similar between all groups, with a median symptom duration of 16.8-34.0 days. Baseline 25OHD was not significantly different between groups [median, interquartile range (IQR): RA 46.7, 30.0-73.3; PsA 41.2, 30.0-65.0; UIA 51.4, 30.0-72.3; CSA 47.7, 30.3-73.0; Other 37.0, 24.9-55.3]. In the RA group (n = 335), there were no significant differences between 25OHD and any measures of disease activity/fatigue. Finally, we found no association between 25OHD and progression from UIA (n = 121) or CSA (n = 150) to RA (p = 0.554 and p = 0.741 respectively).
Conclusion
Overall we found no clear association between serum 25OHD and baseline diagnosis, RA disease activity, or progression from UIA/CSA to RA in this large cohort of early RA patients. Limitations of the study include that we were unable to report on levels of vitamin D metabolites which may be more important than total vitamin D. In addition, we were unable to adjust for supplement use/ time of year the sample was taken due to missing data. Future studies into the role of different metabolites of vitamin D in aetiopathogenesis of inflammatory arthritis would provide invaluable insight into the role of vitamin D in inflammatory arthritis better defining the complex role of vitamin D in RA.
Disclosures
S.R. Harrison: None. G. Jutley: None. D. Li: None. I. Sahbudin: None. A. Filer: None. M. Hewison: None. K. Raza: None.
Circulating Levels of Free 25(OH)D Increase at the Onset of Rheumatoid Arthritis
