Nutritional Supplements and Osteoarthritis
Arthritis is a general term that describes inflammation in joints. Osteoarthritis, also called degenerative joint disease, is the most common type of arthritis. It is associated with a breakdown of cartilage in joints and commonly occurs in the hips, knees, and spine. It also often affects the finger joints, the joint at the base of the thumb, and the joint at the base of the big toe.
Common treatment methods don't change the progression of osteoarthritis. However, two nutritional supplements -- glucosamine and chondroitin sulfates -- are being studied to determine if they can relieve pain or perhaps slow the breakdown of cartilage, which is a significant part of osteoarthritis.
What Is Cartilage?
Cartilage is a firm, rubbery material that covers the ends of bones in normal joints (See Figure 1). Its main function is to reduce friction in the joints and serve as a "shock absorber." The shock-absorbing quality of normal cartilage comes from its ability to change shape when compressed.
Cartilage can change shape because it is more than 70% water, which can be redistributed with movement. For example, when force is applied to a knee, as in standing or walking, some water from cartilage enters the joint and coats the cartilage. When the force is no longer present, such as when you sit down, the water is reabsorbed and the cartilage regains its normal shape. Because cartilage does not contain nerves, you do not feel pain when these changes in shape occur.
Osteoarthritis causes the cartilage in a joint to become stiff and lose its elasticity, making it more susceptible to damage. Over time, the cartilage may wear away in some areas, greatly decreasing its ability to act as a shock absorber. As the cartilage wears away, tendons and ligaments stretch, causing pain. If the condition worsens, the bones could rub against each other.
Cartilage is made up of four substances: collagen, proteoglycans, water, and chondrocytes (see Figure 2).
In addition to being a key component of cartilage, the protein collagen is also found in the skin and tendons. Collagen provides cartilage with its strength, and creates a framework that houses the other components of cartilage.
This substance is a combination of protein and sugar. Proteoglycans are woven around and through collagen, allowing cartilage to change shape when compressed. Proteoglycans trap water in cartilage, which is redistributed with movement.
Healthy cartilage contains more than 70% water. In addition to functioning as the shock absorber in cartilage, it lubricates and nourishes the cartilage.
These cells produce new collagen and proteoglycans in cartilage. Chondrocytes also release enzymes which help break down and dispose of aging collagen and proteoglycans.