TUESDAY, Sept. 30 (HealthDay News) -- The popular supplements glucosamine and chondroitin are no better than a placebo at preventing cartilage loss in knees of people with the form of arthritis caused by wear and tear, a new study found.

Still, the researcher who led the study said glucosamine may help some people with osteoarthritis.

The researcher, Dr. Allen D. Sawitzke, an associate professor of internal medicine at the University of Utah School of Medicine, also acknowledged that the trial wasn't conclusive because of the small number of participants and the relatively short duration -- two years.

Sawitzke said that what struck him as possibly significant was the lower rate of joint loss for participants taking only glucosamine -- 0.013 millimeters, about one-tenth as much as found in those taking either other supplements or a placebo.

"That is not statistically significant, but it hints to me that there might be something going on," he said.

"It was a null study that didn't show a difference," Sawitzke admitted, before adding: "That's not the same as saying there is no difference. The result was influenced by the slow rate of progression for everybody. The study actually says more about what we need to do for the next investigation than for what patients should do."

The new findings, published in the October issue of the journal Arthritis & Rheumatism,, was a continuation of the earlier Glucosamine/chondroitin Arthritis Intervention Trial (GAIT), led by University of Utah researchers.

Arthritis sufferers take glucosamine either to reduce pain or to slow progression of the condition, Sawitzke said. "Controls pain -- this study says nothing about it," he said. "Slows progression -- the study says we weren't able to show that."

For the new study, GAIT participants were given the chance to continue their original study treatment for an additional 18 months, for a total of two years -- 500 milligrams of glucosamine three times a day; 400 milligrams of chondroitin sulfate three times a day; or a combination of the two supplements; 200 milligrams of the pain killer celecoxib (Celebrex) daily; or a placebo.

X-rays were taken at the start of the study and again at one and two years. Joint space width was measured on 581 knees from 357 patients. None of the trial groups showed significant improvement. But the group taking glucosamine had the least change in joint space width, followed by the groups taking chondroitin, celecoxib, a placebo, and the combination of both supplements, the study found.

If someone with arthritis asked his advice about taking glucosamine, Sawitzke said, "I would ask you why you want to. If it is pain, I would try it for a month and, if you felt better, continue. If it is to slow progression, I would say there is insufficient data. It might be years before you know if there is benefit or no benefit."

Andrew Shao, vice president for science and regulatory affairs at the Council for Responsible Nutrition, the supplement industry trade group, said the study "has some severe limitations, because the decline in joint space was much less than the researchers expected."

"The message for consumers," Shao added, "is that this study doesn't provide us with any meaningful insight whatever, and people should continue to use their products."

Previous studies have not been favorable for glucosamine. A Dutch report earlier this year said the supplement didn't help people with arthritis of the hip. And a 2007 review of 15 studies found no convincing evidence that glucosamine works against arthritis.

The picture remains unclear, Sawitzke said.

"I'd hate to give up on something that might have benefit across the board, but at the same time, we don't have evidence that it's there yet," he said.

More information

Learn more about osteoarthritis and its treatment from the U.S. National Library of Medicine.