What is collagen?

In one line

Collagen is the protein that forms the framework of skin, tendons and bones, making tough fibers that hold tissues together and help them withstand pulling.

What is collagen?
The name on skin and joint supplement tubs
On powders and drinks sold for skin or joints, you often see the word 'collagen'. Collagen is actually the name of the most common protein in our own bodies. This post explains, step by step, what collagen is, what it does in the body, and what happens when you eat it.
In one line
The protein that holds the body's framework together
Collagen is the protein that makes up the framework of the body, such as skin, tendons and bones. It forms tough fibers that link and hold different parts of the body together. That is why skin and tendons can be pulled without tearing easily.
First, what is protein?
A chain of pieces called amino acids
Protein is a long chain of small pieces called 'amino acids'. There are 20 kinds of amino acids, and which ones are linked, and in what order, decides which protein you get. Collagen is one of the proteins built by linking amino acids this way.
Where is it in the body?
About 1/3 of the body's protein
Collagen makes up about 1/3 of all the protein in the human body, so it is the body's most common protein. It is the main part of skin, and it is also found in tendons, ligaments, cartilage, bones and blood vessels.
What it looks like
A rope made of three twisted strands
In collagen, three chains of amino acids twist around each other to form one cord. For the three strands to pack tightly, every third spot in each chain must be an amino acid called 'glycine'. Many of these cords then group together into thick, tough fibers.
How the body makes it
Vitamin C is a must
The body builds collagen itself, using amino acids from food as the raw material. Vitamin C is required for this. When vitamin C runs short, wounds heal slowly and gums become inflamed, and a very severe shortage is called 'scurvy'.
Collagen in food
Tough meat and fish skin; boil it and you get gelatin
In food, collagen is found only in animal foods, such as meat with lots of tough tissue and fish bones and skin. Gelatin is what you get when animal bones, cartilage and skin are boiled for a long time and then cooled until they set. When a bone broth cools and turns jelly-like, that is because of this gelatin.
Collagen in supplements
Broken-down 'collagen peptides'
Collagen in supplements is usually a powder of collagen broken into small pieces, called 'hydrolyzed collagen' or 'collagen peptides'. Hydrolyzed means broken into small pieces with the help of water, and a peptide is a short piece made of only a few amino acids linked together. Studies usually used 2.5–15 g a day.
As a protein
An 'incomplete protein' missing tryptophan
9 of the amino acids cannot be made by the body and must come from food; these are called 'essential amino acids'. Collagen contains none of one of them, 'tryptophan'. So by the standard used to grade protein quality, it is classed as an 'incomplete protein'.
Common misconception
Does the collagen you eat go straight to your skin?
No. Like other proteins, collagen is broken down during digestion into amino acids and short pieces of two or three amino acids, and then absorbed. Being absorbed means passing through the gut into the blood. The body uses these as raw material wherever protein is most needed at the time, and the collagen you eat does not travel to the skin and attach there in its original form.
Summary
The most common protein, holding the body's framework together
Collagen is the body's most common protein; it forms the framework of skin, tendons and bones and holds tissues together with tough fibers. The collagen you eat is broken down into amino acids and short pieces before it is absorbed, and it does not attach to the skin in its original form. Related terms: protein, amino acids, vitamin C.