Vitamin D claims for knee osteoarthritis questioned

By Lynda Williams, Senior medwireNews Reporter

The benefit of taking vitamin D supplements for the treatment of knee osteoarthritis (OA) has been challenged in a study published in JAMA.

The 2-year randomized trial shows no improvement in knee pain severity or cartilage volume loss in patients given oral cholecalciferol 2000 IU/day, with dose escalation to achieve a serum 25-hydroxyvitamin 25(OH) D level of 36 ng/mL, and those given placebo.

This level of vitamin D supplementation was chosen after being reported in epidemiologic studies to slow knee OA progression, explain Timothy McAlindon (Tufts Medical Center, Boston, Massachusetts, USA) and co-authors.

The trial enrolled 146 patients, aged an average of 62.4 years, with symptomatic knee OA between 2006 and 2009, and 85% of participants completed the study.

Patients taking supplements increased their 25(OH)D levels by an average of 16.1 ng/mL, compared with a 2.1-mg/mL increase in controls over the study. The target of 36 ng/mL was achieved by 61.3% of patients given supplements compared with just 8.3% of controls.

Baseline knee pain, measured using the Western Ontario and McMaster Universities (WOMAC) pain scale, where 0 equals no pain and 20 equals the extreme pain, was slightly worse in supplemented patients than controls, at an average of 6.9 and 5.8, respectively.

Both patient groups experienced a significant reduction in knee pain over the study and the improvement did not significantly differ between supplemented and placebo-treated patients (-2.31 vs -1.46).

Furthermore, magnetic resonance imaging demonstrated no significant difference in the percentage decrease in knee cartilage volume over the study in the groups, at an average of -4.30% and -4.25% in supplemented patients and controls, respectively.

Nor were there any significant differences between the treatment groups for secondary trial endpoints including change in cartilage thickness, bone marrow lesion size, or radiographic joint space width, the researchers report.

The team acknowledges that the supplement may not have been sufficiently large enough to induce a benefit, but say that sensitivity analysis indicates that patients with a sustained response in vitamin D levels did not show a benefit.

"Thus, although there is a theoretical possibility that greater doses (or higher blood levels) of vitamin D are needed to exert a therapeutic effect, our data do not support this supposition," McAlindon et al conclude.

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