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.
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.
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.
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.
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.