Effect of vitamin D supplementation on knee osteoarthritis: A systematic review and meta-analysis of randomized clinical trials

Objective. To provide evidence regarding the effect of vitamin D supplementation on symptomatic knee osteoarthritis (OA). Methods: A systematic review and meta-analysis was performed to quantitatively pool the results from randomized clinical trials. Studies were identified from a search of the Embase, MEDLINE and Web of Science databases up to January 22, 2017, and also from conference abstracts, ClinicalTrials.gov and the reference lists of identified studies. A standardized mean difference (SMD) was used to assess effect sizes, as outcomes were reported on different scales. Depending on the degree of heterogeneity, random-effects or fixed-effects models were used to pool outcomes. Results: Up to January 22, 2017, four clinical trials containing 570 subjects in the vitamin D supplementation group and 560 subjects in the placebo group were identified. All of the included studies were of high quality and had a low risk of bias for each domain. The results indicated that vitamin D supplementation had a statistically significant but small-to-moderate effect on pain control in patients with knee OA (SMD = -0.32, 95% CI: -0.63 to -0.02). However, no effects were observed for the change in tibial cartilage volume (SMD = 0.12, 95% CI: -0.05 to 0.29) or joint space width (SMD = 0.07, 95% CI: -0.08 to 0.23). The subgroup analysis indicated that vitamin D supplementation had no significant effect regardless of whether patients had sufficient or insufficient serum 25(OH) D levels at baseline. Conclusions: The results of this study indicate that vitamin D supplementation may not have a clinically significant effect on pain control or structure progression among patients with knee OA. Longer-term clinical trials with rigorous measurement of symptom and radiologic changes are required to further clarify the effect of vitamin D supplementation in patients with symptomatic knee OA and low serum 25(OH) D levels.