Background: Animal, epidemiologic, and human clinical studies suggest a putative role for vitamin D in osteoarthritis (OA). Inadequate sunlight exposure and lower serum levels of 25(OH)D appear in some reports to be associated with an increased risk for progression of knee OA.
Questions/purposes: We asked whether treatment with vitamin D would (1) reduce knee pain (WOMAC and VAS), (2) improve function (WOMAC), and (3) change levels of relevant biochemical markers in patients with knee OA with vitamin D insufficiency.
Methods: This randomized controlled pilot trial prospectively enrolled 107 patients with knee OA with vitamin D insufficiency (25(OH)D ≤ 50 nmol/L) to receive oral vitamin D or placebo. The primary outcome measures were pain and function, and the secondary were biochemical markers. At baseline, the two groups were comparable. The patients were followed for 1 year.
Results: At 12 months, knee pain had decreased in the vitamin D group by mean -0.26 (95% CI, -2.82 to -1.43) on VAS and -0.55 (95% CI, -0.07 to 1.02) on the WOMAC, whereas in the placebo group, it increased by mean 0.13 (95% CI, -0.03 to 0.29) on the VAS and 1.16 (95% CI, 0.82 to 1.49) on the WOMAC (effect size = 0.37 and 0.78). Likewise knee function improved in the vitamin D group by mean -1.36 (95% CI, -1.87 to -0.85) over the placebo group which had a mean 0.69 (95% CI, -0.03 to 1.41; effect size = 0.06). There were significant biochemical changes in serum total calcium, 25(OH)D and alkaline phosphatase.
Conclusions: The results above suggest there is a small but statistically significant clinical benefit to vitamin D treatment in patients with knee OA, although we recommend a long-term study to determine whether these changes are clinically important and whether they will be sustained with time. Further studies with long-term radiologic evaluations are needed.