Supplements containing glucosamine, chondroitin sulfate, or a combination of the two have been widely touted as treatments for the pain caused by osteoarthritis of the knees.
In theory, these supplements make sense. Osteoarthritis is caused by progressive wearing away of joint cartilage, which serves as a cushion that keeps the bones in the joint from rubbing painfully against one another. Glucosamine is required for the formation and repair of glycosaminoglycans, critical components of cartilage, while chondroitin is the most abundant component of the glycosaminoglycans. So, the idea is that taking these two components of cartilage by mouth will maintain the integrity of joint cartilage.
In fact, however, no evidence has been found that glucosamine or chondroitin can be absorbed intact from the intestine, can ever reach the joints, or, once there, can be incorporated into cartilage.
Between November 2000 and July 2004, the National Institutes of Health sponsored the Glucosamine/Chondroitin Arthritis Intervention Trial (GAIT). GAIT enrolled 1,229 participants with mild knee pain and 354 subjects with moderate-to-severe pain in 16 U.S. centers. Participants were randomly assigned to take either 1) glucosamine alone, 2) chondroitin sulfate alone, 3) a combination of glucosamine and chondroitin sulfate, 4) the painkiller celecoxib, or 5) a placebo.
After 6 months, the subjects taking celecoxib reported a significant improvement in pain (defined as 20 percent or more reduction in pain compared to that experienced at the start of the study). By contrast, overall pain relief was no greater in participants taking any of the supplements compared with those taking the placebo, especially in those with mild pain.
In the smaller group of participants with moderate-to-severe pain, the combination of glucosamine with chondroitin provided statistically significant pain relief in 79 percent compared with 54 percent in the placebo group. Additional studies are needed to confirm these findings because of the small number of subjects in the group with more than mild pain.
The GAIT trail also sought to determine whether these dietary supplements could reduce the progression of structural damage in the knees. Interested patients were offered the opportunity to continue taking their original treatments for an additional 18 months. After this 2-year treatment period, however, x-rays of 581 knees revealed no differences in the loss of cartilage with any of the 5 forms of treatment.
In summary then, the supplements may offer some relief for those with more severe pain, but they neither help those with mild pain nor slow the deterioration of cartilage in the knees.
Many people with knee osteoarthritis will undoubtedly continue to take these supplements and will feel confident that their pain is improved, just as many in GAIT's placebo group reported significantly less pain. The good news is that no significant adverse effects were reported from taking these supplements—other than their costs.
