Origin: Chondroitin is a component of human connective tissues found in cartilage and bone. In supplements, chondroitin sulfate usually comes from animal cartilage.

Claims: Reduces pain and inflammation, improves joint function and slows progression of osteoarthritis (OA).

What we know: Believed to enhance the shock-absorbing properties of collagen and block enzymes that break down cartilage. Helps cartilage retain water and may reverse cartilage loss when used with glucosamine.

Studies: The largest study to date, the 2006 Glucosamine/chondroitin Arthritis Intervention Trial (GAIT) looked at 1,600 people with knee OA. The first phase found that a small subset of patients with moderate-to-severe arthritis experienced significant pain relief from combined glucosamine and chondroitin. The 2008 phase found that glucosamine and chondroitin, together or alone, did not slow joint damage. And in the two-year-long 2010 phase, glucosamine and chondroitin were found as effective for knee OA as celecoxib (Celebrex).

But a 2010 meta-analysis of 10 trials involving more than 3,000 patients published in BMJ found no benefit from chondroitin, glucosamine or both.

A separate 2011 study showed a significant improvement in pain and function in patients with hand OA using chondroitin alone. Benefits of chondroitin and glucosamine remain controversial, but the supplements appear extremely safe.

Dosage: Capsules, tablets and powder; 800 mg to 1,200 mg daily in two to four divided doses. Often combined with glucosamine. Allow up to one month to notice effect.

Some chondroitin tablets may contain high levels of manganese, which could be problematic with long-term use. Because chondroitin is made from bovine products, there is the remote possibility of contamination associated with mad cow disease. Chondroitin taken with blood-thinning medication like NSAIDs may increase the risk of bleeding. If you are allergic to sulfonamides, start with a low dose of chondroitin sulfate and watch for any side effects. Other side effects include diarrhea, constipation and abdominal pain.