Part of a large protein molecule (proteoglycan) that gives cartilage elasticity. It is commonly obtained from cartilage extracts, mainly bovine. It can also be obtained from sea cucumber, green lipped mussels and shark cartilage. Useful in the treatment of osteoarthritis, it attracts water into joints, which act as a shock absorber as well as a nutrient transport system. Chondroitin is closely related to glucosamine and is usually combined with it for additional benefit.