A systematic review and meta-analysis of the effects of vitamin D on inflammatory and clinical outcomes in patients with rheumatoid arthritis (RA)

Background: Vitamin D deficiency is commonly in patients with rheumatoid arthritis, and a meta-analysis based on observational data showed that vitamin D supplementation reduced disease activity. Aim: To investigate whether vitamin D supplementation affects the inflammatory and clinical outcomes in patients with rheumatoid arthritis. Material and Methods: Literature was searched in the Cochrane Central Register, PubMed, MEDLINE, Embase, and Google Scholar. Cochrane guidelines were used with a random effects model. Of 464 publications, 11 studies were included (3049 patients). All with a placebo or a different dose of vitamin D as controls. Only one study used vitamin D with calcium. Results: Vitamin D supplementation did not reduce C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), disease activity score in 28 joints (DAS28), or health assessment questionnaire score (HAQ), but heterogeneity was marked. Vitamin D significantly reduced pain in VAS, DAS28–CRP, and DAS28–ESR. Subgroup analysis for vitamin D doses (>100 µg per day versus <100 µg per day) showed, that high doses had better effect on CRP than the low doses (P < 0.05). There was no dose effect on ESR and DAS28. Subgroup analysis for blinded versus open-label design showed no effect on CRP, but some effect on ESR (P = 0.08). The open-label study design had a significant effect on pain-VAS. Conclusions: There are minor effects of Vitamin D supplementation to patients with rheumatoid arthritis. In future studies, factors such as sun exposure, drug interaction, and dosage of vitamin D should be included.