Objectives To describe whether maintaining sufficient serum vitamin D levels in people with knee osteoarthritis (OA) and baseline vitamin D insufficiency has an association with change in knee structures and symptoms over two years.

Methods Participants (n=413, age 63.2; 50% females) with symptomatic knee OA and vitamin D insufficiency were enrolled in a clinical trial. 340 participants (82.3%) completed the study with 25-hydroxyvitamin D [25(OH)D] measurements at month 0, 3 and 24. Participants were classified as consistently insufficient (serum 25(OH)D ≤50nmol/l at month 3 and 24, n=45), fluctuating (25(OH)D >50nmol/l at either point, n=68) and consistently sufficient (25(OH)D >50nmol/l at month 3 and 24, n=226) vitamin D groups. Knee cartilage volume, cartilage defects, bone marrow lesions (BMLs) and effusion-synovitis volume were assessed using MRI at baseline and month 24. Knee symptoms were assessed at baseline, month 3, 6 12 and 24 using Western Ontario and McMaster Universities Arthritis Index (WOMAC).

Results The consistently sufficient group had significantly less loss of tibial cartilage volume (β: 2.1%, 95 CI%: 0.3%, 3.9%), less increase in effusion-synovitis volume (β: -2.5ml, 95 CI%: -4.7, -0.2) and less loss of WOMAC physical function (β: -94.2, 95% CI: -183.8, -4.5) compared to the consistently insufficient group in multivariable analyses. In contrast, there were no significant differences in these outcomes between the fluctuating and consistently insufficient groups. Changes in tibiofemoral cartilage defects, BMLs and knee pain were similar between groups.

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Conclusions This post hoc analysis suggests beneficial effects of maintaining vitamin D sufficiency on cartilage loss, effusion-synovitis and physical function in people with symptomatic knee OA.

References

1. Cao, Y., et al., Vitamin D supplementation in the management of knee osteoarthritis: study protocol for a randomized controlled trial. Trials 2012;13:131.

2. Jin, X., et al., Effect of Vitamin D Supplementation on Tibial Cartilage Volume and Knee Pain Among Patients With Symptomatic Knee Osteoarthritis: A Randomized Clinical Trial. JAMA 2016; 315(10):1005–13.

References

Acknowledgements We specially thank the participants who made this study possible, and we gratefully acknowledge the role of Vitamin D Effect on Osteoarthritis Study staff and volunteers in collecting the data. We thank the research assistants Jodi Barling, Kay Nguo, Judy Hankin and Alice Noone who were involved in the coordination of this study.

Disclosure of Interest None declared