Collagen is made from amino acids, primarily glycine, proline, and hydroxyproline, arranged in a unique triple-helix structure that gives your skin, bones, and connective tissues their strength. In supplements, collagen comes from animal tissues like cow hides, pig skin, fish scales, and bones, which are broken down into smaller peptides your body can absorb. The answer depends on whether you’re asking about what your body uses to build collagen naturally or what goes into the powder you stir into your coffee.
What Collagen Looks Like at the Molecular Level
Collagen has a structure unlike any other protein in your body. Three individual protein strands wind around each other to form a rope-like triple helix. Every third amino acid in each strand is glycine, the smallest amino acid, which tucks neatly into the center of the helix because its tiny side chain doesn’t crowd the other strands. This repeating pattern (glycine every third position) is what allows the three strands to wrap tightly together.
The strands are offset from each other by one amino acid, which lines up glycine on one strand directly across from a neighboring amino acid on the adjacent strand. This alignment creates hydrogen bonds running sideways across the helix, essentially stitching the three strands together. These lateral bonds are what give collagen its remarkable tensile strength, making it resistant to stretching in the same way a braided rope is stronger than three loose strings.
A chemical modification called hydroxylation is critical to the whole structure. Certain proline amino acids get an added oxygen-hydrogen group after the protein chain is assembled. This modification increases the thermal stability of the helix, meaning it holds its shape at body temperature instead of unraveling. Without it, collagen falls apart. This is exactly why vitamin C deficiency causes scurvy: vitamin C is required for that hydroxylation step, and without it, your body produces unstable collagen that can’t do its job.
The Three Main Types in Your Body
Your body contains at least 28 types of collagen, but three account for the vast majority.
- Type I is the most abundant protein in the human body. It forms densely packed fibers that provide structure to skin, bones, tendons, and ligaments.
- Type II is found in elastic cartilage, where it provides cushioning and joint support.
- Type III is present in muscles, arteries, and organs, often alongside Type I but in softer, more flexible tissues.
These types differ in how their triple helices are assembled and cross-linked, which determines whether the resulting tissue is rigid like bone or stretchy like skin.
What Your Body Needs to Make Collagen
Your cells build collagen from amino acids obtained through digestion of any protein-rich food. The process starts inside specialized cells (fibroblasts in skin, osteoblasts in bone) that assemble long chains of amino acids into a precursor molecule. That precursor gets chemically modified, folded into the triple helix, and then exported outside the cell, where enzymes trim it and cross-link it into mature collagen fibers.
Several nutrients are essential cofactors in this process. Vitamin C is the most important: it’s required for the hydroxylation step that stabilizes the triple helix. Zinc is needed for the enzymes that produce Type I and Type III collagen and for the cross-linking that gives collagen its durability. Copper also plays a role in cross-linking collagen fibers together. Without adequate levels of these nutrients, your body’s collagen production slows or produces weaker fibers, regardless of how much protein you eat.
Where Supplement Collagen Comes From
Commercial collagen supplements are sourced from animal connective tissues. The primary sources are calf skin and bone (bovine collagen), pig skin (porcine collagen), and fish skin and scales (marine collagen). These tissues are rich in collagen because that’s what connective tissue is largely made of.
Bovine collagen is the most widely used in the supplement industry. It comes from cattle hides, bones, and tendons, often as a byproduct of the meat industry. Marine collagen, typically from fish skin or scales, has gained popularity partly because it avoids beef and pork for people with dietary restrictions. Porcine collagen is more common in medical and food-industry applications than in consumer supplements, though it appears in both.
There is no plant-based collagen. Plants don’t produce collagen. Products marketed as “vegan collagen” typically contain the amino acid building blocks and cofactors (like vitamin C and zinc) that support your body’s own collagen production, but they don’t contain actual collagen protein.
How Raw Tissue Becomes a Supplement
Native collagen from animal tissue is a massive, tightly wound molecule that your digestive system can’t absorb efficiently. Manufacturers break it down through a process called hydrolysis, using enzymes or acid to cut the long collagen chains into much smaller fragments called peptides.
The goal is to produce peptides small enough to pass through the intestinal wall. Research on enzymatic hydrolysis has produced collagen fragments ranging from roughly 500 to 2,100 daltons, which is small enough for efficient absorption. Multiple enzymes are often used in combination to achieve the smallest possible peptide size. The result is hydrolyzed collagen (also labeled “collagen peptides”), a powder that dissolves easily in liquid because the molecules are far smaller than intact collagen.
Gelatin is a middle step in this process. It’s partially hydrolyzed collagen: the triple helix has been broken apart, but the chains haven’t been cut into small peptides. That’s why gelatin dissolves only in hot water and gels when it cools, while collagen peptides dissolve in cold water and don’t gel.
How Your Body Absorbs Collagen Peptides
When you consume hydrolyzed collagen, your digestive enzymes break most of it into individual amino acids and very small peptides (two or three amino acids linked together). These small peptides are absorbed in the small intestine through a specific transporter called PepT1, which pulls them into intestinal cells along with hydrogen ions.
Once inside the intestinal cells, most of these peptides are broken down further into individual amino acids before entering the bloodstream. Only a very small number of intact peptides make it into blood. This means your body isn’t absorbing collagen and depositing it directly into your skin or joints. Instead, it’s receiving amino acids, particularly glycine, proline, and hydroxyproline, that it can use as raw materials to build new collagen wherever it’s needed.
Some research suggests that certain small peptides, especially those containing hydroxyproline, may survive digestion intact and signal fibroblasts to ramp up collagen production. This signaling effect, rather than direct incorporation, is one proposed explanation for the skin and joint benefits observed in clinical trials of collagen supplements.
Purity and Contamination Concerns
Because collagen is derived from animal bones and skin, there’s inherent concern about heavy metal contamination. Bones accumulate metals like lead and cadmium over an animal’s lifetime, and these can carry over into collagen products. Industry specifications for collagen supplements typically set limits at 0.50 parts per million or lower for lead, 0.10 ppm for cadmium, 0.02 ppm for mercury, and 0.70 ppm for arsenic.
Quality varies across brands. Third-party testing from organizations like NSF International or ConsumerLab can verify whether a product meets these thresholds. Marine collagen from fish may carry different contamination profiles than bovine collagen, depending on the water source and species. If purity matters to you, look for products that publish their certificate of analysis or carry a third-party testing seal.