Collagen is a protein that makes up about 25% of the proteins in the human body. There are 14 different types of collagen, with Type II being the most predominant.
It is important to the structural integrity of connective tissue located throughout most of the body, especially bones, cartilages, tendons, and ligaments.

Collagen for human supplementation may be obtained from different sources and in different forms: marine versions can contain up to 90% pure type II collagen (Collagen HM®), 75-85% type II collagen together with 23-28% chondroitin sulphate and minerals as well (Glycollagen®) or 60-70% collagen plus 35-40% CS (Protein M®).

Bovine versions are also available.

Image credits: Nevit Dilmen [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0/)]