Association between vitamin D intake and the risk of rheumatoid arthritis: a meta-analysis.

The aim of this study was to summarize published results on the association between vitamin D intake and the development of rheumatoid arthritis (RA) and between serum vitamin D levels and RA activity. Evidence of a relationship between vitamin D intake and the development of RA and between serum vitamin D levels and RA activity was studied by summarizing published results using a meta-analysis approach. Three cohort studies including 215,757 participants and 874 incident cases of RA were considered in this meta-analysis, and eight studies on the association between serum vitamin D levels and RA activity involving 2,885 RA patients and 1,084 controls were included. Meta-analysis showed an association between total vitamin D intake and RA incidence (relative risk (RR) of the highest vs. the lowest group = 0.758, 95 % confidence interval (CI) 0.577-0.937, p = 0.047), without between-study heterogeneity (I(2) = 0 %, p = 0.595). Individuals in the highest group for total vitamin D intake were found to have a 24.2 % lower risk of developing RA than those in the lowest group. Subgroup meta-analysis also showed a significant association between vitamin D supplement intake and RA incidence (RR 0.764, 95 % CI 0.628-0.930, p = 0.007), without between-study heterogeneity. All studies, except for one, found that vitamin D levels are inversely associated with RA activity. One study found no correlation between vitamin D levels and disease activity among 85 RA patients, but these patients had a high incidence of vitamin D deficiency, which might have influenced the study outcome. Meta-analysis of 215,757 participants suggests that low vitamin D intake is associated with an elevated risk of RA development. Furthermore, available evidence indicates that vitamin D level is associated with RA activity.