Study: Among patients with symptomatic knee osteoarthritis and low serum 25-hydroxyvitamin D levels, vitamin D supplementation, compared with placebo, did not result in significant differences in change in MRI-measured tibial cartilage volume or WOMAC knee pain score over 2 years. These findings do not support the use of vitamin D supplementation for preventing tibial cartilage loss or improving WOMAC knee pain in patients with knee osteoarthritis.

http://jama.jamanetwork.com/article.aspx?articleid=2499277