Adults with osteoarthritis in the knees who take vitamin D supplements did not show an improvement in pain relief or cartilage loss, according to a new study published in JAMA.

The study was a two year randomized trial consisting of patients with symptomatic knee osteoarthritis.

The authors explain in background information:

“Knee osteoarthritis (OA) is a common age-related musculoskeletal disorder that has significant functional impact and has considerable societal costs through work loss, early retirement, and arthroplasty. Despite its impact, there are no medical treatments established to influence the course of the disease. Some studies have suggested that vitamin D may protect against structural progression.”

The clinical trial conducted by Timothy McAlindon, D.M., M.P.H., of Tufts Medical Center, Boston, and his co-workers, analyzed whether taking vitamin D supplements is linked with a decrease in symptomatic and structural advancement of osteoarthritis (OA).

The placebo-controlled clinical trial was made up of 146 patients with symptomatic knee OA who were on average 62 years of age; 61 percent of them were women. The subjects were enrolled in the study between March 2006 and June 2009.

Study volunteers received either a placebo or oral cholecalciferol, 2,000 IU/day, with dosage increase to up serum levels to over 36 ng/mL. Just 85 percent of the subjects finished the study.

The principal outcomes for the study were cartilage volume loss which was calculated by magnetic resonance imaging (MRI), and the extent of their knee pain, calculated by the Western Ontario and McMaster Universities pain scale: 0-20; 0, no pain and 20 the most pain imaginable.

Other secondary outcomes monitored include the following:

  • radiographic joint space width
  • cartilage thickness
  • bone marrow lesions
  • knee function (WOMAC function scale 0-68; 0, no difficulty, 68 extreme difficulty)
  • physical function

Vitamin D levels rose by an average of 16.1 ng/mL within the group receiving treatment and an average of 2.1 ng/mL in the placebo group. Knee pain at the start of the study was worse in the group receiving treatment (6.9) than in the placebo group (5.8). Knee function at the start was much worse in the vitamin D group (22.7) compared with the placebo group (18.5).

In the subset assessments for the WOMAC pain outcome, the results were similar, but not noteworthy. Findings showed that knee pain was reduced in both groups by an average of -2.31 in the vitamin D group and -1.46 in the placebo group, with no important variations at any time. Percentage of cartilage volume was reduced by the same amount in both groups, around 4 percent.

There were no significant variations in any of the secondary outcomes. Also experienced were 31 major adverse events in the vitamin D group and 23 in the placebo group, however the number of participants who had these effects in each group was just 16.

The authors conclude:

“Additional results from epidemiological studies that emerged during the course of this study have been mixed demonstrating positive and negative associations. Two studies appeared to show strong associations of bone density with the development of knee OA, but some of those investigators later published concerns about the possibility of such associations arising as a result of contingent confounding. Therefore, together with the results of this clinical trial, the overall data suggest that vitamin D supplementation at a dose sufficient to elevate 25-hydroxyvitamin D levels to more than 36 ng/mL does not have major effects on clinical or structural outcomes in knee OA, at least in a U.S. sample.”

A previous study from 2010 linked rheumatoid arthritis (RA) and vitamin D deficiency. The authors pointed out the risk for RA was higher in northern regions where there is less sunlight, suggesting a link between the illness and the deficiency.

Written by Kelly Fitzgerald