Cartilage repairs not seen in studies

Question: I recently read online that the supplement I take for my knee pain probably doesn't work. I use a chondroitin sulfate glucosamine mixture from my local health-food store. I thought it helped but now I wonder if I should keep taking the supplement.

Answer: The original idea was deceptively simple and had a certain elegant logic: Our joints are cushioned and protected by cartilage, which can get worn down over time, so eating powdered cartilage should help replenish our natural cartilage. Furthermore, cartilage is pretty much the same from one source to another. It can be obtained from the most abundant, cheapest source -- usually shark cartilage.

The concept's flaw is that it does not take into account cartilage metabolism. Cartilage contains chondroitin sulfate, a large protein that gives cartilage its elasticity. It also contains glucosamine, a complex sugar known as a mucopolysaccharide. Glucosamine causes cartilage to retain water, a good thing. It simulates production of a joint lubricant, has an anti-inflammatory property and can speed healing of damaged cartilage. Complex metabolic pathways produce both, however. The fallacy comes in thinking that all we have to do is eat cartilage and somehow it will reach our damaged joints and repair them.

While chondroitin and glucosamine supplements may be sold separately, most joint supplements include both. Consumers spend more than $800 million a year on these supplements alone to treat arthritis. Dietary supplements are regulated as foods, not drugs, and do not have to meet strict requirements for safety and effectiveness demanded by the Food and Drug Administration.

A recent article in The Annals of Internal Medicine reported on an evaluation of 20 studies focusing on the effectiveness of chondroitin in treating arthritis. Of these, only three were considered sufficiently well-designed to yield valid conclusions. These did not support the use of chondroitin for relieving the pain of osteoarthritis, the most common form of arthritis older adults experience. One reason may be that chondroitin is poorly absorbed through the gastrointestinal tract when taken by mouth. Studies show that only about 5 percent of the chondroitin you take by mouth is absorbed and available to have any effect.

In contrast, when glucosamine is taken in by mouth, 89 percent is absorbed in the GI tract and more than 25 percent is available in the first pass as it circulates through the body. Studies in which researchers label glucosamine with a radioactive isotope -- and administer it orally -- show a significant amount of the labeled material turns up in joint cartilage and in surrounding ligaments and tendons, making it at least available to have some beneficial effect.

Because pain relief is difficult to measure, some patients undoubtedly benefit from the placebo effect. It would be better if measurable regeneration of damaged or worn cartilage could be demonstrated in conjunction with pain relief, but so far such studies are lacking.

Until more is known, there is probably no harm, and some possible good, derived from taking a joint supplement. However, it appears the real active ingredient is the glucosamine, not the chondroitin. The usual recommended dose of glucosamine is 1,500 milligrams per day.

As with all supplements, try to find one that is stamped "USP." This means it meets standards for potency and availability by the United States Pharmacopoeia.