Glucosamine

A substance found naturally in healthy cartilage. Evidence from some studies suggests that supplements containing glucosamine may help relieve the symptoms of osteoarthritis (OA). As a supplement, glucosamine is often taken in combination with chondroitin, another substance found naturally in cartilage. There are two main preparations of glucosamine found in supplements: glucosamine hydrochloride and glucosamine sulfate. Glucosamine sulfate has been studied more closely in clinical trials.

Cartilage is the tough, smooth tissue that lines the ends of bones where they meet to form a joint. Cartilage helps the joint move easily and absorb the stresses of regular use. In people with OA, cartilage grows brittle and wears away, allowing bones to rub against each other and causing pain and stiffness in the joint. Some researchers theorize that because glucosamine plays an important role in keeping cartilage healthy, glucosamine supplements can help rejuvenate cartilage and thereby relieve the symptoms of OA.

However, the effectiveness of glucosamine remains uncertain. There have been more than 20 controlled clinical trials of glucosamine (mostly glucosamine sulfate). Some have shown that glucosamine can relieve pain and slow cartilage breakdown; many others have found that glucosamine has no significant effect.

The largest clinical study of the effects of glucosamine on OA was the Glucosamine/Chondroitin Arthritis Intervention Trial (GAIT), sponsored by the National Institutes of Health. GAIT enrolled 1,583 people aged 40 and older who had knee pain and x-ray evidence of OA. Of these, 78% had mild knee pain and 22% had moderate-to-severe knee pain. The participants were split into five groups, with each group getting one of the following treatments: glucosamine hydrochloride alone; chondroitin alone; glucosamine and chondroitin in combination; celecoxib (Celebrex), a prescription anti-inflammatory drug; or an inactive treatment (placebo). All participants were followed for about six months and were evaluated periodically.

The study found that, for most people, neither glucosamine nor chondroitin relieved OA symptoms more than placebo. However, for a small subset of participants — those with moderate-to-severe pain — glucosamine combined with chondroitin provided statistically significant pain relief compared with placebo. Because the study was not designed to look at subsets separately, however, the study’s researchers consider these results preliminary and not conclusive.

A two-year continuation of the GAIT study found that neither glucosamine nor chondroitin, either alone or in combination, slowed the rate of cartilage loss as seen on x-rays more than placebo. However, the cartilage loss in participants taking placebo was less than expected, complicating the results and pointing to the need for further study.

Glucosamine is considered safe and has few major side effects when taken in standard doses. However, people should be sure to tell their doctors before they take it and never use it in place of their arthritis medicines. (Talking to your doctor is especially important in the case of glucosamine–chondroitin combinations, which may enhance the effects of some blood thinners.) The standard dose of glucosamine is 1,500 milligrams (mg) daily, whether or not it is taken with chondroitin.

People who take glucosamine, however, should note that not all glucosamine is created equal. Most is derived from crab, lobster, or shrimp shells, although there are shellfish-free formulations that may be helpful for people with shellfish allergies. Because regulations for dietary supplements are not stringent, some glucosamine supplements may not have the advertised amounts of active ingredients. A study by Consumerlab.com found that many glucosamine–chondroitin combination products contain less chondroitin than the amount listed on their label. When buying supplements, be sure to look for reputable brands or those carrying the United States Pharmacopeia (USP) seal or a symbol from NSF International or ConsumerLab.com.

Robert S. Dinsmoor is a medical writer and editor based in Massachusetts.

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