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Background: Vitamin D has been implicated as being involved in the aetio-pathogenesis 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.

Objectives: 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 of the Northern Sweden.

Methods: Blood samples donated to the Medical Biobank prior to 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) vitamin 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 (OR 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 however, associated with an increased risk of disease in females carrying the minor allele of a DBP encoding SNP.

Acknowledgements: Samples and data for the cohort were obtained through the Västerbotten Intervention Program, the Northern Sweden MONICA Study, and the mammary screening program of Västerbotten. Staff of the Department of Biobank Research, Umeå University, aided in acquisition of samples and data.