Study finds vitamin D supplement does not reduce knee osteoarthritis progression

Adding vitamin D as a supplement does not appear to lessen the symptoms, or slow the progression, of knee osteoarthritis, according to research presented this week at the American College of Rheumatology Annual Scientific Meeting in Atlanta.

Osteoarthritis, or OA as it is commonly called, is the most common joint disease affecting middle-age and older people. It is characterized by progressive damage to the joint cartilage—the cushioning material at the end of long bones—and causes changes in the structures around the joint. These changes can include fluid accumulation, bony overgrowth, and loosening and weakness of muscles and tendons, all of which may limit movement and cause pain and swelling.

Vitamin D promotes the absorption of calcium and phosphorus needed for bone mineralization, growth and repair. Sources of vitamin D are available to a lesser extent from dietary sources typically found in fortified margarine, oily fish, liver, fortified breakfast cereals and dairy products. Sun exposure helps vitamin D to become active.

Previous studies have suggested that vitamin D may reduce the structural progression of knee OA, and researchers recently studied 146 people who showed symptoms of knee OA to determine if taking vitamin D would be an effective way of treating the disease. The participants were predominately Caucasian women with an average age of just over 62 years. Their average body mass index was 30.7, their average vitamin D level was 22.3 ng/ml-1, and their average femoral neck bone mineral density was .92 gcm-2. Additionally, 56 percent of the participants were taking supplements.

The researchers divided participants evenly into two groups. The first group was assigned to take placebo, and the second group was assigned to take vitamin D throughout the course of the study. Participants were not told which group they had been placed in. Those in the vitamin D group started by taking 2,000 IU of vitamin D daily, and this was raised as necessary over the course of the study in 2,000 IU increments to help each participant achieve a vitamin D level higher than 30 ng/ml.

The researchers also performed physical function tests and X-rays on each participant at the beginning of the study and again at 12 months. And, they computed the knee cartilage volume and thickness, bone marrow lesion volume from the MRIs taken at the beginning of the study and again at 12 months to determine if any changes had occurred.

At the end of the study, the participants in the vitamin D group had an average vitamin D level increase of 15 ng/ml (compared to only 1.8 ng/ml in the placebo group), but researchers found no substantial differences between the two groups in the areas studied - leading them to believe that those taking vitamin D did not benefit more than those who were not.

"This study tested whether vitamin D supplementation, given over a two-year period, could influence the rate of progression of joint damage in people with knee osteoarthritis," explains Timothy McAlindon, MD, MPH; associate professor of medicine, division of rheumatology, Tufts New England Medical Center and lead investigator in the study. "The vitamin D doses were increased as necessary to elevate participants' serum levels to over 30 ng/ml. The study found no difference compared to a placebo (inert) treatment."

Patients should talk to their rheumatologists to determine their best course of treatment.