Umeå University's logo

Objectives: Vitamin D has been implicated as being involved in the aetiopathogenesis of several autoimmune diseases including rheumatoid arthritis (RA). Previous studies present contradictory results. Vitamin D binding protein (DBP), the major transport protein, is also involved in various inflammatory processes. The aim of this study was to investigate the relationship between circulating levels of 25-hydroxyvitamin D [25(OH)D], DBP, and polymorphisms in group-specific component (GC) in pre-symptomatic individuals and matched controls within prospective cohorts in northern Sweden.

Methods: Blood samples donated to the Medical Biobank before the onset of symptoms of RA (n = 515, mean ± sd time before the onset of symptoms 6.2 ± 9.3 years) and from matched (2:1) population-based controls (n = 267) were used. Plasma 25(OH)D levels were analysed using liquid chromatography–tandem mass spectrometry and DBP levels were analysed using enzyme-linked immunosorbent assay. GC polymorphisms (rs4588 and rs7041) were analysed with TaqMan assays (Applied Biosystems).

Results: Levels of 25(OH)D or DBP were not statistically different between pre-symptomatic individuals and controls in a crude or a multiple-adjusted logistic regression model. However, an increased risk for future RA was found in females of DBP (odds ratio 1.0001, 95% CI 1.000–1.0003), adjusted for carriage of the minor allele of rs4588, in a multiple-adjusted model (p < 0.05).

Conclusions: This study indicated that vitamin D is not associated with the future risk of RA, although increasing levels of DBP were associated with an increased risk of disease in females carrying the minor allele of a DBP encoding SNP.