Background/Purpose: To examine whether those maintaining sufficient serum vitamin D levels have reduced knee structural changes and symptomatic improvement compared with those not maintaining sufficient serum vitamin D levels over 2 years in patients with knee osteoarthritis (OA).

Methods: Participants (n= 413, age 63.2; 50% females) with symptomatic knee OA and vitamin D insufficiency were enrolled in a multicentre, parallel randomized, placebo-controlled and double-blind clinical trial. 340 participants (82.3%) completed the study as well as 25-hydroxyvitamin D [25(OH)D] measurements at month 3 and month 24. In the post-hoc analyses, participants were classified as maintaining insufficient vitamin D group (Group 1, serum 25(OH)D≤50nmol/l at month 3 and month 24, n=45), fluctuating vitamin D group (Group 2, 25(OH)D>50nmol/l only at one point, n=68) and maintaining sufficient vitamin D group (Group 3, 25(OH)D>50nmol/l at month 3 and month 24, n=226). Serum 25(OH)D were measured at baseline, month 3 and month 24 using direct competitive chemiluminescent immunoassays. Knee structural changes including cartilage volume, cartilage defects, bone marrow lesions (BML) and effusion-synovitis volume were assessed using magnetic response imaging (MRI) at baseline and month 24. Knee pain was assessed at baseline, month 3, 6 12 and 24 using Western Ontario and McMaster Universities Arthritis Index (WOMAC) and visual analogue scale.

Results: Patients in Group 3 had significantly less tibial cartilage volume loss per year (β: 2.2, 95% CI: 0.4, 4.0) and change in effusion-synovitis volume per year (β: -69.5, 95% CI: -133.4, -5.6) than participants in Group 1 (Figure 1 and Figure 2). The differences remained significantly after further adjustment for age, sex, BMI and season of blood sampling (β: 2.1, 95 CI%: 0.3, 3.9 and β: -61.8, 95 CI%: -121.9, -1.7, respectively). There were no significant differences in changes of tibiofemoral cartilage defects and BML between Group 3 and other two groups. Patients in Group 3 had significantly less loss of WOMAC physical function (β: -94.8, 95% CI: -183.1, -6.6) than others two groups in the mixed-effect models.

Conclusion: Patients maintaining sufficient serum vitamin D at month 3 and 24 had less cartilage volume loss, less increase in effusion-synovitis volume and more improvement in physical function compared with those not maintaining sufficient serum vitamin D over 2 years in symptomatic knee OA patients with vitamin D insufficiency. These findings suggesting that maintaining sufficient 25(OH)D is beneficial for structural change and functional improvement in knee osteoarthritis.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/maintaining-sufficient-serum-vitamin-d-levels-over-2-years-is-associated-with-reduced-knee-structural-and-symptomatic-changes-in-patients-with-knee-osteoarthritis/