Tier 3 — preclinical

Identification of food-derived collagen peptides in human blood after oral ingestion of gelatin hydrolysates

Koji Iwai, Takanori Hasegawa, Yasuki Taguchi, Fumiki Morimatsu, Kenji Sato, Yasushi Nakamura, Akane Higashi, Yasuhiro Kido, Yukihiro Nakabo, Kozo Ohtsuki

Journal of Agricultural and Food Chemistry 2005 53(16):6531–6536

Bibliography

DOI: 10.1021/jf050206p
PubMed: PMID 16076145
Funding: No external grant funding statement disclosed in the paper. Acknowledgment: "We thank Nitta gelatin for providing porcine type I gelatin hydrolysate (SCP-5000)."
Competing interests: No competing interests statement disclosed in the paper. Three co-authors (Takanori Hasegawa, Yasuki Taguchi, Fumiki Morimatsu) were employees of Nippon Meat Packers Research and Development Center at time of publication — a commercial producer of gelatin hydrolysate products. The porcine hydrolysate was gifted by Nitta Gelatin. Remaining co-authors were affiliated with Kyoto Prefectural University. Substantial industry involvement despite the absence of a formal declaration.

Study snapshot

Design	Open-label, single-dose, two-experiment human bioavailability study
Model	Healthy Japanese adult volunteers
Sample	12 total (Experiment 1: n=5 aged 21–39, 45–80 kg; Experiment 2: n=7 males aged 25–37, 47–67 kg)
Intervention	Single oral dose of gelatin hydrolysate after 12 h fast. Exp 1: 9.4 g porcine skin type I hydrolysate (SCP-5000). Exp 2: 23 g chicken feet type I (C-LAP) or 11 g chicken cartilage type II (C-mucolla) per 60 kg body weight.
Duration	Single-dose kinetics; blood sampling 0–180 min (Exp 1) and 0–270 min with one subject to 24 h (Exp 2)
Endpoints	Peptide-form hydroxyproline plasma concentration and time course; Identification of collagen-derived peptide sequences by RP-HPLC and Edman degradation; Semi-quantitative peptide composition per source; In vitro Pro-Hyp digestibility by human serum peptidase

What the study showed, in plain terms

Collagen is a protein found in skin, bones, tendons and cartilage. When people take a collagen supplement, the collagen is broken down in the gut into much smaller pieces called peptides. For a long time, scientists were not sure whether any of these peptides actually made it into the bloodstream, or whether they were fully digested into single amino acids first. If they made it into the blood intact, they might carry signals to the skin and joints. If not, taking collagen would be no different from eating any other protein.

This 2005 study was the first to clearly answer that question in humans. Twelve healthy volunteers each took a single dose of gelatin hydrolysate (a form of collagen that has already been partly broken down in a factory) on an empty stomach, and the researchers took blood samples over the next several hours. They then used sensitive lab techniques to look for tiny two- and three-amino-acid fragments that could only have come from collagen.

The peptides showed up in the blood within about 30 to 60 minutes, peaked, then slowly cleared over the next few hours. One peptide in particular — called Pro-Hyp — turned out to be the dominant piece. Follow-up experiments showed Pro-Hyp resists being broken down by enzymes in the blood, which explains why it lingers. The paper is the foundational proof that some collagen peptides survive digestion and reach the bloodstream intact, opening the door to every downstream question about whether they then act on skin, joints or bones.

Key findings

Peptide-form hydroxyproline reached maximum plasma concentration 30–60 minutes post-ingestion, at levels of 20–60 nmol/mL, then declined to half of maximum by roughly 4 hours.
The ratio of peptide-form hydroxyproline to free hydroxyproline in plasma was approximately 1:3 across all three gelatin sources tested.
Pro-Hyp dominated the plasma peptide profile: 95% of detected collagen peptides after porcine type I gelatin, 92% after chicken type I, and roughly 70% after chicken type II.
Minor peptides identified included Ala-Hyp-Gly, Pro-Hyp-Gly, Ile-Hyp, Leu-Hyp and Phe-Hyp, each present at low single-digit percentages except after chicken type II ingestion, where Pro-Hyp-Gly reached 19% and Leu-Hyp reached 5%.
Pro-Hyp was resistant to human serum peptidase: after 24 hours of in vitro incubation at 37 °C, only about a quarter of the hydroxyproline in Pro-Hyp had been liberated.
Peptide-form hydroxyproline plasma level returned to baseline by 12 hours post-ingestion in the one subject sampled that long.

What this study can and cannot tell us

Very small sample sizes (n=5 in Experiment 1, n=7 in Experiment 2) — plasma peptide levels showed wide individual variation, and no statistical inference about population means is warranted.
Open-label with no placebo or non-collagen protein control. The paper is descriptive of what appears in blood after collagen ingestion, not comparative.
Single-dose only. No data on whether peptide plasma levels rise, plateau or fall with repeated daily ingestion.
All subjects were Japanese. No inference about inter-ethnic differences in gut peptide transporter expression or peptide absorption kinetics.
Substantial industry involvement — three co-authors were employed by Nippon Meat Packers, a commercial gelatin hydrolysate manufacturer, and the porcine hydrolysate was gifted by Nitta Gelatin. No competing interests statement is provided.
Peptide identification was by semi-quantitative Edman sequencing of RP-HPLC peaks. Absolute quantification requires stable-isotope-labelled internal standards, which were not used.
The study establishes that collagen-derived peptides reach the bloodstream. It does not measure whether they reach skin, joint or bone tissue, and does not measure any biological effect at any site.