Taking collagen is not the same as building collagen. This distinction, which seems obvious once the biology is understood, is key to understanding why oral collagen works—when it does—and why not all collagen supplements produce the same effects. The mechanism goes far beyond "you eat it and it turns into skin."
From collagen to peptide: what happens during digestion
When hydrolyzed collagen is ingested, the peptide chains pass through the stomach—where the acidic pH and gastric proteases partially fragment them—and reach the small intestine, where the action of pancreatic and intestinal peptidases reduces them to smaller fragments. Most of the ingested collagen is digested into free amino acids (glycine, proline, hydroxyproline), which pass into the blood like any other dietary amino acid.
But a fraction—the most biologically interesting—is absorbed as intact peptides: di- and tripeptides that the intestine can transport through active transport systems (especially the PepT1 transporter). It is this fraction that has signaling activity on fibroblasts, and it is what distinguishes a quality hydrolyzed collagen from a simple source of glycine and proline.
Di- and tripeptides: the forms the body recognizes as a signal
The most relevant studies on the mechanism of action of oral collagen have identified two specific dipeptides as the most active signals on dermal fibroblasts: Pro-Hyp (prolyl-hydroxyproline) and Hyp-Gly (hydroxyprolyl-glycine). These peptides are detected in blood plasma after ingestion of hydrolyzed collagen, and have been shown in vitro to stimulate fibroblast proliferation, increase type I procollagen synthesis, and stimulate hyaluronic acid production by synovial and dermal fibroblasts.
Shigemura et al. and Liu et al. have published studies documenting the presence of Pro-Hyp in human plasma after ingestion of hydrolyzed gelatin and hydrolyzed collagen, and its mitogenic activity on fibroblasts in culture. These are the mechanisms that provide scientific basis for the effects observed in clinical trials with Peptan® and other reference hydrolysates.
Fibroblasts and endogenous synthesis: the real mechanism of action
Dermal fibroblasts are the cells responsible for synthesizing collagen, elastin, and hyaluronic acid in the dermis. When they receive the signal from circulating bioactive peptides—especially Pro-Hyp—through receptors on their membrane, they respond by increasing the expression of genes encoding type I procollagen and activating the synthesis pathways of the extracellular matrix. This mechanism is analogous to what occurs after tissue damage: the body interprets collagen peptides as a signal that the extracellular matrix needs renewal.
This is the mechanism that explains why "dose" matters so much: a sufficient plasma concentration of bioactive peptides is needed to consistently activate fibroblasts. Insufficient doses produce subthreshold signals that do not generate the documented synthesis response in studies.
Peptan® and studies on specific collagen peptides
Peptan® by Rousselot is the marine collagen hydrolysate with the largest number of published studies on its content of specific bioactive peptides. Its low molecular weight profile (mostly <3,000 daltons) ensures efficient generation of di- and tripeptides after digestion. Studies with Peptan® have documented its presence in human plasma and its activity on fibroblasts in in vitro and in vivo models, providing the mechanistic basis that supports the observed clinical results.
Why the molecular weight of the hydrolysate determines the type of response
High molecular weight hydrolysates—fragments >10,000 daltons—are digested into free amino acids more efficiently and produce fewer intact bioactive peptides. Low molecular weight hydrolysates—<3,000 daltons—generate a higher proportion of absorbable di- and tripeptides. This is not a difference in degree: it is a difference in mechanism. A well-characterized low molecular weight hydrolysate is functionally different from a high molecular weight one, even though both are called "hydrolyzed collagen" on the label.
What this implies for formulation
The mechanism of bioactive peptides implies that what matters in a collagen supplement is not the gross amount of "collagen" on the label, but rather: the molecular weight of the hydrolysate (which determines the generation of bioactive peptides), the source and hydrolysis process (which determine the peptide profile), the dose (which determines the plasma concentration of the signal), and cofactors (which determine whether fibroblasts can respond to the signal). LEVIAL was designed with all these factors in mind. That's the difference between a formula with logic and a list of ingredients.
