The supplements glucosamine and chondroitin sulfate, taken together or alone, failed to show a clear advantage over placebo as a treatment to slow the progression of osteoarthritis of the knee.
There was a suggestion that taking glucosamine alone might be beneficial, lead researcher Allen D. Sawitzke, MD, of the University of Utah School of Medicine, tells WebMD. But the two-year study was not large enough or long enough to show this.
"I would definitely not want the message from this study to be that these supplements don't work at all," he says. "That would be a disservice because they might prove valuable in future studies."
Glucosamine, Chondroitin Used by Millions
The latest findings are an extension of the National Institutes of Health-funded Glucosamine/chondroitin Arthritis Intervention Trial (GAIT).
In 2006, GAIT researchers reported that the supplements were not much better than placebo for reducing knee pain associated with osteoarthritis. Researchers followed close to 1,600 patients who took one or both of the supplements, the painkiller Celebrex, or placebo for six months.
Some benefit was seen in patients with moderate to severe pain who took both glucosamine and chondroitin, but the finding was not conclusive because only a small number of patients in the study had pain that was considered moderate to severe.
In an effort to determine if the supplements help slow the destruction of knee cartilage, 572 of the original GAIT participants continued to take their original study treatment for an additional 18 months. All these patients had moderate to severe osteoarthritis.
The researchers used a specific X-ray protocol to determine the rate of osteoarthritis progression over time.
After two years, there was no significant difference between treatment and placebo groups.
"While we found a trend toward improvement among those with milder osteoarthritis of the knee in those taking glucosamine alone, we were not able to draw any definite conclusions," Sawitzke says.
Interpretation of the results was also complicated by the fact that the placebo group had less arthritis progression during the two-year study than the researchers had predicted.
The X-ray protocol used to measure osteoarthritis progression also proved to be less than optimal, says Josephine Briggs, MD, who directs the NIH's National Center for Complementary and Alternative Medicine, which co-sponsored the study.
Briggs tells WebMD that better ways of measuring osteoarthritis progression may be on the horizon, including the use of MRI.
"To really understand the promise of these interventions our measures must be maximally sensitive," she says.
The latest GAIT findings appear in the October issue of the journal Arthritis & Rheumatism.
What Should Patients Do?
Roughly 21 million American have osteoarthritis. While many patients end up having surgery to replace worn-out knees, Sawitzke says there are few nonsurgical treatments that address disease progression.
"Right now we essentially have nothing to offer," he says.
He recommends that people who want to try one of the supplements use glucosamine alone rather than glucosamine and chondroitin because there is some evidence that glucosamine absorption is compromised with the combination treatment.
"I tell my patients who want to take it for pain to try it for a few weeks or a month," he says. "That should be long enough to tell if it is working for you."
The GAIT study and others suggest that glucosamine and chondroitin are safe supplements, but Briggs says patients who take them or any supplement should always discuss it with their doctor.
She says more than two out of three adults in the U.S. use some type of complementary or alternative medicine, but only about one in three tell their physicians about it.
"It is important to discuss any medication you take with your doctor, including complementary and alternative medicines," she says.