Your body uses glucosamine, a natural compound, to create one of the main building blocks of joint cartilage -- proteoglycans. As you age, the amount of glucosamine created by the body decreases. This causes cartilage and bones to scrape against each other. Joints become damaged, and the lubricating synovial fluid in joint spaces becomes thin and watery. Supplementing your diet with glucosamine may help to replenish these fluids.