Tier 2 — strong

Glycine Bioavailability and Sleep-Related Outcomes Following Oral Glycine and Collagen Supplementation-A Scoping Review

Fan Z, Nelson JM, Wallace TC
Journal of dietary supplements 2026 23(5):602-622

Bibliography

PubMed
PMID 42687500
DOI
10.1080/19390211.2026.2726197
Funding
Funding was not specified in the indexed abstract; the full funding disclosure has not been verified.
Competing interests
The accessible abstract does not establish the authors' competing interests; absence of a statement is not evidence of no conflicts.

Study snapshot

DesignScoping review of human supplement trials
ModelHuman studies
Sample21 records describing 22 unique trials
InterventionOral glycine, collagen and other glycine-containing supplements; no new intervention
DurationLiterature searched through 9 July 2026
EndpointsCirculating glycine availability; Sleep outcomes; Fatigue and recovery

What the study showed, in plain terms

This 2026 review maps human exposure and sleep studies. It separates free glycine from collagen and asks whether glycine could explain collagen-related findings. It does not demonstrate that glycine mediates those effects.

Key findings

  • Three trials examined supplemental glycine and sleep-related outcomes.
  • Fourteen trials examined pharmacokinetic availability; five collagen-related trials were reported across four records.
  • At least one outcome favored glycine in each sleep trial, but collagen comparisons were mixed.

What this study can and cannot tell us

A scoping review does not provide a pooled efficacy effect or independently solve bias in the underlying studies.

Higher blood glycine after collagen is not proof that collagen and isolated glycine have identical sleep effects.

Related papers in the corpus

Tier 2
Subjective effects of glycine ingestion before bedtime on sleep quality
Inagawa K et al. · Sleep and Biological Rhythms · 2006
Tier 2
Glycine ingestion improves subjective sleep quality in human volunteers, correlating with polysomnographic changes
Yamadera W et al. · Sleep and Biological Rhythms · 2007
Tier 2
The effects of glycine on subjective daytime performance in partially sleep-restricted healthy volunteers
Bannai M et al. · Frontiers in neurology · 2012
Tier 4
New therapeutic strategy for amino acid medicine: glycine improves the quality of sleep
Bannai M et al. · Journal of pharmacological sciences · 2012
Tier 3
The sleep-promoting and hypothermic effects of glycine are mediated by NMDA receptors in the suprachiasmatic nucleus
Kawai N et al. · Neuropsychopharmacology : official publication of the American College of Neuropsychopharmacology · 2015
Tier 2
The effect of glycine administration on the characteristics of physiological systems in human adults: A systematic review
Soh J et al. · GeroScience · 2024

Editorial review

Reviewed by the Biohack Blueprint research team

Last verified

Dr. Khaled Mahmoud, MBBChCritical Care Medicine, Longevity Science & Editorial Direction