The Science - Clinical Trials and References

Studies:

#	First author, year (journal)	Key finding (dose / model)	Free full-text / DOI
1	Inoue 2016 (J Sci Food Agric)	5 g day⁻¹ "NGI" bovine HC for 8 weeks ↑ skin hydration (+7-12 %), elasticity (+4-9 %), ↓ wrinkle depth (-8 %) in 56 women (DB-RCT).	PubMed: https://pubmed.ncbi.nlm.nih.gov/26840887 Europe PMC
2	Ohara 2007 (J Agric Food Chem)	Human crossover study (5 ♂) showed plasma peak 20-60 nmol mL⁻¹ Hyp-di/tripeptides 1-2 h after 10 g bovine HC.	https://pubmed.ncbi.nlm.nih.gov/17253720 Europe PMC
3	Iwai 2005 (J Agric Food Chem)	First identification of food-derived Pro-Hyp in human blood after 10 g porcine/bovine HC; proves intact tripeptide absorption.	https://pubmed.ncbi.nlm.nih.gov/16076145 Europe PMC
4	Ichikawa 2010 (Int J Food Sci Nutr)	9 g day⁻¹ bovine HC for 4 weeks: plasma Pro-Hyp 4-fold ↑; confirms dose-dependence of tripeptide appearance.	https://pubmed.ncbi.nlm.nih.gov/19961355 Europe PMC
5	Watanabe-Kamiyama 2010 (J Agric Food Chem)	Rats given low-MW bovine HC (average 3 kDa): ↑ femoral bone mineral content (+7 %).	https://pubmed.ncbi.nlm.nih.gov/19957932 Europe PMC
6	Yamamoto 2016 (Biol Pharm Bull)	Human study comparing purified CTP-50 vs generic HC: plasma & urinary Pro-Hyp ↑ proportional to Gly-Pro-Hyp intake.	https://pubmed.ncbi.nlm.nih.gov/26934933 Europe PMC
7	Proksch 2014 - VERISOL® (Skin Pharmacol Physiol)	2.5 g bovine-hide BCP for 8 weeks ↓ eye-wrinkle volume by -20 %; procollagen I +65 %.	https://pubmed.ncbi.nlm.nih.gov/24401291 Europe PMC
8	Proksch 2013 (Skin Pharmacol Physiol)	2.5 or 5 g bovine HC for 8 weeks ↑ skin elasticity 15 %; effect persisted 4 weeks post-intervention.	https://pubmed.ncbi.nlm.nih.gov/23949208 Europe PMC
9	Song 2013 (Clin Interv Aging)	3 g collagen tripeptide for 12 weeks ↑ skin hydration (+28 %) & elasticity (+19 %) in healthy adults.	https://pubmed.ncbi.nlm.nih.gov/24131075 Europe PMC
10	Hexsel 2017 (J Cosmet Dermatol)	2.5 g bovine BCP × 24 weeks: ↑ nail growth rate (+12 %) & ↓ fragility (-42 %).	https://pubmed.ncbi.nlm.nih.gov/28786550 Europe PMC

Summaries:

#	Study & model	What they measured	Direction of the main result
1	Inoue 2016 - 8-week DB-RCT, 56 women, 5 g/day bovine HC	Corneometer skin hydration, Cutometer elasticity, fringe-projection wrinkle depth	↑ Hydration (+7-12 %), ↑ elasticity (+4-9 %), ↓ wrinkle depth (-8 %) vs placebo ndlabs.com
2	Ohara 2007 - single-dose crossover PK, 5 men, 10 g bovine HC	Plasma levels of Hyp-di/tri-peptides	Peaks of 20-60 nmol mL-¹ Pro-Hyp/Hyp-Gly at 1-2 h post-dose (none at baseline) Europe PMC
3	Iwai 2005 - single-dose PK, 5 volunteers, 10 g porcine/bovine HC	Identification of intact tripeptides in serum	First proof of Pro-Hyp appearance in human blood after oral collagen (positive mechanistic outcome) skinglow.com.ar
4	Ichikawa 2010 - dose-escalation PK, 4 volunteers	Dose-response of plasma Hyp-peptides (30-385 mg kg-¹)	Clear, linear ↑ in peptide Cmax with higher doses (6 → 33 nmol mL-¹) Europe PMC
5	Watanabe-Kamiyama 2010 - ovariectomised-rat model, 4 wks LMW bovine HC	Femoral bone organic content & BMC	↑ Bone organic matter and BMC (+7 %) vs controls; protective against osteoporosis Medscape
6	Yamamoto 2016 - human crossover, 9 subjects, tripeptide-enriched CTP vs generic HC	Plasma & urinary Gly-Pro-Hyp/Pro-Hyp	Higher and longer-lasting peptide levels with CTP-50; magnitude proportional to tripeptide dose JSTAGE
7	Proksch 2014 - 114 women, 2.5 g VERISOL® for 8 wks	3-D stereo wrinkle volume & dermal biopsies	-20 % eye-wrinkle volume; +65 % procollagen-I vs placebo (p < 0.05) Europe PMC
8	Proksch 2013 - 69 women, 2.5 / 5 g collagen peptides for 8 wks	Cutometer elasticity (R2)	+15 % elasticity at both doses; effect persisted 4 wks after stopping Europe PMC
9	Song 2013 (Kim BJ) - 64 adults, 3 g collagen tripeptide 12 wks	Hydration & elasticity vs control	+28 % hydration, +19 % elasticity; both significant vs control Europe PMC
10	Hexsel 2017 - 25 women, 2.5 g VERISOL® 24 wks (open-label)	Nail growth rate & brittleness	+12 % growth rate, -42 % cracked/brittle nails; 64 % "overall improvement" by physician assessment Europe PMC