An Update of the Promise of Glycine Supplementation for Enhancing Physical Performance and Recovery.
Level 5 - mechanism / opinion, no new human data
Narrative literature review summarizing preclinical and limited clinical evidence
PubMed 39453231 · doi:10.3390/sports12100265
What was done
This narrative literature review evaluated preclinical (cell, in vitro, animal) and human studies examining glycine supplementation for muscle metabolism, protection against muscle wasting, peak power output, lactic acid accumulation, endurance exercise performance, and sleep quality.
What was found
The abstract reports no quantitative data or effect sizes. It qualitatively reports that glycine activates anabolic pathways, inhibits proteolytic gene expression, and may enhance peak power output, reduce lactic acid accumulation, and improve sleep and recovery. It notes that high doses (>500 mg/kg of body mass) could cause cytotoxic effects and contribute to acute glutamate toxicity.
Why it matters
Glycine is widely available and biologically relevant to muscle metabolism, but evidence for performance enhancement remains largely mechanistic. This paper identifies potential therapeutic targets while underscoring the lack of established nutritional recommendations for athletes.
Limits
As a narrative review, it lacks systematic search methodology, quality assessment, and pooled data. Much of the underlying evidence relies on in vitro and animal models rather than well-controlled human randomized trials.
Cited by
- partial Magnesium L-threonate, L-theanine, chamomile extract, and glycine are clinically supported ingredients that can improve sleep latency, sleep maintenance, and morning refreshment.