Collagen is the largest protein in a human body, made up of thousand amino acids. It builds connective tissues through out the body to support joints, muscles and to rejuvenate the skin.
Some connective tissue diseases and other diseases, mainly because of a weak immune system, can cause the collagen to degenerate. One of them is rheumatoid arthritis which affects the joints, causing pain, swelling and stiffness in the joints.
Collagen is said to stimulate the growth of new cartilage, which is a thin tissue enveloping the joints. However, cartilage is dependent on collagen so when the body lacks collagen, it causes pain, stiffness and instability of the joints.