106 patients, over the age of 40, who met the American college of Rheumatology criteria for knee OA were randomly assigned into 1 of 2 groups: a placebo or a vitamin D supplement group. The purpose was to determine if treatment with vitamin D effectively reduced pain, improved function, and changed levels of relevant biochemical markers in patients with knee OA. The results of the study indicated that after 12 months, knee pain was significantly different between the two groups, in favour of the vitamin D intervention. Knee function also improved significantly in patients who received vitamin D. Significant biochemical changes in serum total calcium, 25(OH)D, and alkaline phosphate levels were found between the groups.