Vitamin D Does Not Improve Pain, Function, or Joint Space Width in Knee OA

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Researchers assessed the effectiveness of vitamin D supplementation in patients with knee osteoarthritis.

Daily vitamin D supplementation of at least 1000 International Units (IUs) did not significantly improve knee pain, physical function, or joint space width in patients with knee osteoarthritis (OA) after 24 months, according to study findings published in Osteoarthritis and Cartilage.

Researchers conducted a systematic review of the literature published in English between January 1, 1990, and December 31, 2019, on PubMed, EMBASE, and the Cochrane Central Register of Controlled Trials. They analyzed the effect of vitamin D supplementation on knee OA using target trial emulation.

Four eligible randomized control trials were identified, into which they subdivided patients with knee OA into 2 treatment groups: participants in the intervention group (n=236) received at least 1000 IU of vitamin D supplements for at least 4 days/week for 30 days and those in the control group (n=1320) did not take vitamin D supplementation.

Length of follow-up was adjusted for all studies up to 30 months from study onset because vitamin D levels require 3 to 6 months to replenish and achieve levels stable enough to impact arthritic joints.

The effects of vitamin D supplementation on knee OA pain and physical function as measured by the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), as well as quantitative joint space width as measured on radiographic imaging.

Based on optimal pair-matched analysis, knee OA pain did not change significantly between the treatment and control groups after 24 months (standard mean deviation [SMD]=-0.04, CI: -0.21 to 0.13). Both groups also demonstrated lower physical function levels after 24 months without significant differences (SMD=-0.02, 95% CI: -0.17 to 0.14). Both the intervention and control groups demonstrated similar narrowing of joint space widths after 24 months (SMD=-0.07, 95% CI: -0.27 to 0.12).

Similar results we observed between the intervention and control groups for each of the outcome measures in the inverse probability treatment weighting (IPTW) analysis.

Limitations of the study included a lack of exact data of initiating vitamin D supplementation, which introduced potential treatment misclassification bias, and a lack of assessment of vitamin D levels at baseline and at follow-up visits to verify vitamin D insufficiency and confirm replenishment with supplementation. This study used radiographic imaging to ascertain knee OA progression, whereas magnetic resonance imaging may more accurately reflect OA changes.

The study authors concluded, “This study is a first step in demonstrating that target trial emulation using observational data can be used to test the effectiveness of treatments for osteoarthritis.” They added, “[G]iven the absence of effective disease-modifying osteoarthritis drugs, knowledge about the relative effectiveness and safety of osteoarthritis treatments is needed to inform clinical decision making.”

Disclosures: Some study authors declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of authors’ disclosures.


Jin X, Ding C, Hunter DJ, Gallego B. Effectiveness of vitamin D supplementation on knee osteoarthritis – A target trial emulation study using data from the Osteoarthritis Initiative cohort. Osteoarthritis Cartilage. Published online June 25, 2022:S1063-4584(22)00769-5. doi:10.1016/j.joca.2022.06.005