With more than 46 million Americans diagnosed with arthritis, the market for joint pain supplements is enormous.
Two supplements lead the pack in terms of popularity: glucosamine and chondroitin, both natural components of joint tissue. The compounds come in various forms, with studies suggesting that some work better than others.
The first study hinting that glucosamine and chondroitin in any form might help relieve the pain of inflamed joints was published in 1969. But that and many other early studies were small, short or used supplements of inconsistent type and quality.
More recently, large-scale, well-designed studies have examined two supplements, usually in people with knee osteoarthritis, one of the most common forms of arthritis.
Results have been mixed.
In 2006, researchers at the University of Utah published results of the Glucosamine/Chondroitin Arthritis Intervention Trial, a study of more than 1,500 adults with knee osteoarthritis, randomized to take either glucosamine, a form of chondroitin called chondroitin sulfate, both, a prescription anti-inflammatory drug or a placebo daily for six months.
Neither glucosamine nor chondroitin sulfate -- taken alone or together -- worked much better than the placebo, the researchers found. But for the combination of glucosamine plus chondroitin sulfate, 79% of people with severe pain experienced relief compared with just over half of the placebo group. Overall, the prescription drug provided the most relief -- and did so faster than the supplements or placebo.
Last year, Dr. Thomas Vangsness, professor of orthopedic surgery and chief of sports medicine at the USC Keck School of Medicine, and colleagues published a review of the most rigorous studies. They found that the bulk of studies show that glucosamine (in the various forms that have been studied) and chondroitin sulfate do reduce knee osteoarthritis pain when taken together, although results are inconsistent, with some studies showing no effect.
Another review, by a group of U.S. and Canadian researchers, was published last year by the Cochrane Collaboration, a nonprofit organization that reviews the science on health topics. Analyzing data from the 25 top studies on glucosamine alone for arthritis, they found that, on average, the supplements result in a 22% reduction in pain, but, again, in some studies the supplements worked no better than a placebo.
The review also noted that glucosamine seemed to work best to reduce knee pain in studies that used a standardized, prescription form of glucosamine sulfate sold in Europe, made by the German company Rottapharm.
The findings on Rottapharm's glucosamine sulfate constitute the best evidence in favor of the compound to date, says study author Dr. Marc Hochberg, professor of medicine and head of the division of rheumatology and clinical immunology at the University of Maryland School of Medicine.
It's not altogether surprising that some supplements would do better than others. In the U.S., supplements are regulated less stringently than prescription drugs. As a result, different brands may contain slightly different amounts or different forms of the promised compound. "It's a problem," Vangsness says.
The problem is complicated by the fact that glucosamine comes in several forms (including glucosamine, glucosamine sulfate and glucosamine hydrochloride) but only glucosamine sulfate has shown the potential to reduce pain. Most evidence seems to support the use of chondroitin sulfate over other chondroitin forms.
The daily doses used in most studies are 1,500 milligrams of glucosamine and 1,200 mg of chondroitin. Based on existing evidence, taking both appears more likely to reduce joint pain than taking either one alone.
But the mixed results have led to a divide among doctors. Vangsness, for example, says he recommends glucosamine sulfate and chondroitin to every one of his arthritis patients, but Hochberg says he doesn't.
If there's one good piece of news for people with arthritis pain, it's this: Side effects of both supplements are rare to nonexistent. So at least they're safe for those who want to give them a try.