Two popular supplements used against arthritis and joint pain, glucosamine and chondroitin sulfate, proved to be as efficient as placebo in slowing the progress of the disease, a two-year study released on Monday showed.

But in spite of the findings, which have been published on the Web site of the journal Arthritis & Rheumatism, researchers said further study had to be conducted to eliminate any doubt. "I'm most worried about throwing out something that may possibly be a benefit," said study author Dr. Allen D. Sawitzke, associate professor of internal medicine at the University of Utah School of Medicine.

However, Dr. Sawitzke said he would neither hearten nor dishearten people from taking the supplements. "We didn't run into safety issues, so if a patient wants to try them, I don't see a reason to say no. But I can't recommend it; there's no supportive data that says it works," he stated.

The two-year study is a follow-up to a large 2006 study sponsored by the National Institutes of Health which aimed at establishing if the supplements performed better than sugar pills or the drug Celebrex in easing pain in people suffering from osteoarthritis. The findings proved they didn’t.

The later study was carried out at nine sites and sponsored by the National Center for Complementary and Alternative Medicine at the National Institutes of Health. Patients with the same problems were given the supplements, sugar pills or Celebrex, an anti-inflammatory medication used in the treatment of osteoarthritis, rheumatoid arthritis and acute pain. Sawitzke and his colleagues tried to find whether the space between their knee joints became smaller, a measure demonstrating if the cartilage was breaking down. Overall, the supplements didn’t work better than the placebo to slow the loss of knee cartilage in osteoarthritis.

As the Nutrition Business Journal reported, the combination glucosamine chondroitin is the sixth-top-selling dietary supplement in the United States. Its sales toped $831 million in 2007 only.

When hearing the news, some admitted to have been disappointed. Greg Gardner, a rheumatologist at the University of Washington in Seattle, advised patients in the past to at least try the dietary supplements because they were safe and not expensive. But currently he doesn’t think like that anymore. "I probably won't tout it any more as potentially disease-modifying," Gardner said.

More than 21 million American people suffer from osteoarthritis, the most common form of arthritis, and many of them either take one or both supplements. According to Dr. Stephen Katz, head of the NIH's National Institute of Arthritis and Musculoskeletal and Skin Diseases, the factors that play a role in the development of osteoarthritis are age, gender, obesity, genetics and joint injuries.

572 volunteers participated in the trial that lasted a year and a half. Sawitzke’s team found that the supplements (400 mg of chondroitin sulfate three times a day, 500 mg of glucosamine three times a day, a mixture of both, 200 mg of celecoxib once a day or a placebo) didn’t show the slowing of the loss of cartilage. The disease aggravated in 24 percent of patients who took the supplements, the percentage being similar to those who took placebo.