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). 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. 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. 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. •VD had a significant but small-to-moderate effect on pain control in knee OA.•VD had no effects on the change in tibial cartilage volume or joint space width.•VD had no effect whether patients had sufficient serum 25(OH)D levels or not.