Once-daily supplementation with vitamin D—at doses sufficient to raise plasma levels of 25-hydroxyvitamin D to >36 ng/ml—for 2 years did not reduce the symptoms or progression of knee osteoarthritis (OA) in a randomized, placebo-controlled trial in 146 patients with symptomatic knee OA. Knee pain severity and cartilage volume loss were similar in the treatment and control groups, and no differences were seen in functional outcomes between the two groups.