Despite their effectiveness for reducing the pain of knee osteoarthritis, the dietary supplements glucosamine and chondroitin sulfate appear to be no better than placebo at slowing the progression of the cartilage-depleting disease.

In 572 patients with moderate to severe knee OA, researchers from the multicenter GAIT (Glucosamine/chondroitin Arthritis Intervention Trial) study group found that mean cartilage loss after two years was not significantly different in those who took glucosamine, chondroitin, both, or the COX−2 inhibitor celecoxib than in those who took placebo. Cartilage loss was assessed in terms of joint space width, the space visible on an x−ray between the tibia and femur, which shrinks over time in patients with knee OA as the cartilage that normally provides a cushion between those two bones dissipates.

Surprisingly, the patients who experienced the greatest JSW losses were those taking a combination of glucosamine and chondroitin...

"At two years, no treatment showed what we determined to be a clinically important reduction in joint space width loss," said Allen D. Sawitzke, MD, an associate professor of medicine at the University of Utah and first author of the study, which was published in the October issue of Arthritis & Rheumatism.

However, the authors noted that the joint space width (JSW) loss rates seen in the placebo group were much lower than expected, likely because the rates reported in the literature at the time the GAIT study was being designed were based on x−ray measurement techniques that have since become much more precise. This limited the statistical power of the GAIT data for determining significant differences between treatment groups.

That said, the study did identify two trends that are likely to be explored in future trials. Evidence of treatment effectiveness relative to placebo tended to be seen in patients with x−ray evidence of moderate osteoarthritis (grade 2 on the Kellgren−Lawrence scale of OA severity). Of the patients with severe OA (grade 3), conversely, those in active treatment groups tended to have more JSW loss at two years than those in the placebo group.

Surprisingly, the patients who experienced the greatest JSW losses were those taking a combination of glucosamine and chondroitin, even though the two supplements are often marketed in combination. Other pharmacologic studies have suggested that glucosamine may be absorbed less effectively in the presence of chondroitin sulfate. However, the combination treatment group in the GAIT study also included more grade 3 patients than the groups taking either supplement alone, which might have affected the results. Grade 2 patients taking glucosamine alone experienced the least amount of JSW loss at two years.