What is L-Glycine (L-Glycine)?
L-Glycine is the simplest amino acid (its side chain consists of a single hydrogen atom). It is a 'conditionally essential' amino acid that can be synthesized in the body. It constitutes about one-third of collagen, serves as a precursor in the synthesis of glutathione and creatine, and functions as an inhibitory neurotransmitter in the central nervous system.
- CAS number: 56-40-6
- Molecular formula: C₂H₅NO₂
What is L-Glycine Used For? Why is it Used?
Due to its central role in collagen and glutathione synthesis, L-Glycine is preferred in formulations focused on connective tissue, recovery, and sleep. Although small randomized studies show promise for sleep quality and glutathione status, evidence for a direct effect on sports performance is currently limited.
Usage as a Sports Nutrition Product
The following information is based on sports nutrition research (ISSN position stands, randomized controlled trials, and meta-analyses); the level of evidence is clearly stated for each item.
- Collagen synthesis and connective tissue: Glycine is the primary amino acid of collagen; studies have reported that intake of glycine-rich collagen peptide (15 g, before bed) reduces sleep fragmentation and may contribute to tendon/joint health in physically active men (evidence is emerging).
- Sleep and recovery: Good sleep is fundamental to recovery; 3 g of glycine may improve subjective sleep quality and reduce daytime fatigue. Direct performance RCTs in athletes are limited — honestly, the evidence is not yet mature.
- Antioxidant (glutathione) support: Intense exercise increases oxidative stress; glycine contributes to antioxidant defense as a glutathione substrate. More human RCTs are needed to demonstrate performance benefits.
Forms and Differences
L-Glycine is available in different forms; the choice of form depends on bioavailability, stability, and intended use:
- Glycine (free form): Glycine is the simplest amino acid without a chiral center; therefore, it has no 'L' and 'D' isomers (single form). Food and supplement-grade glycine is produced via fermentation or chemical synthesis, is highly soluble in water, and has a slightly sweet taste.
- Sodium glycinate (E640 sodium salt): The sodium salt of glycine; used in food as an acidity regulator/buffer and flavor enhancer.
Usage in Dietary Supplements
- Sleep quality support: Small human studies show that 3 g of glycine taken before bed improves subjective sleep quality and shortens the time to fall asleep/deep sleep (Yamadera 2007).
- Glutathione precursor: Glycine is one of the three amino acids in glutathione synthesis; randomized studies have reported that GlyNAC (glycine combined with N-acetylcysteine) improves glutathione levels and mitochondrial function in older adults.
Usage in the Food Industry
- Flavor enhancer and sweetener (E640): Glycine and its sodium salt are approved in the EU under the additive number E640 as flavor enhancers and mild sweeteners; they mask bitter/unwanted taste notes and are used in beverages, processed meats, soups, and sauces.
- Buffer and pH regulator: Sodium glycinate is used as an acidity regulator/buffer to ensure stable pH in products.
Effects on Health
- Collagen building block: Glycine is every third residue in the collagen triple helix; it is structurally essential for skin, tendon, cartilage, and bone matrix (established physiology).
- Glutathione and creatine synthesis: It serves as a precursor in the synthesis of cellular antioxidant glutathione and creatine for muscle energy.
- Inhibitory neurotransmitter: It functions as an inhibitory neurotransmitter in the spinal cord and brainstem; it is an NMDA receptor co-agonist.
Status of Health Claims (EFSA) — Transparent Information
Glycine (E640) is considered safe when used as a food additive within permitted amounts. However, there is no authorized specific health claim in the EU Register of Nutrition and Health Claims (Reg. 1924/2006) for glycine regarding sleep, recovery, or performance. The statements here are not claims but information based on established physiology and small RCTs.
Usage Limits and Safety
- Typical usage dose: 3 g/day (before bed) in sleep studies; 3-5 g is common in general supplementation
- Upper Limit (UL): No established UL; low doses are well tolerated. Very high doses should be avoided (honestly: no definitive human UL exists).
- Turkish legislation (Sports Foods / TETGK): E640 is approved as a food additive in the Turkish Food Codex; it is also used as a supplement amino acid. I could not verify a specific numerical upper limit for glycine supplements — the number is NOT FABRICATED.
Consult a physician during pregnancy/breastfeeding and in individuals using neurological medications.
Technical Specifications
| Parameter | Value |
|---|---|
| Moisture | ≤5.0 % |
| Total Heavy Metals | ≤10 ppm |
| E. Coli | Negative in 10 g |
| Salmonella | Negative in 25 g |
| Solubility | Soluble in Water |
Scientific Studies
The following independent researches relate to the sports performance, bioavailability, and effects of this compound (study types are specified):
- PubMed 22529837 — Effects of glycine on subjective daytime performance in healthy volunteers with partial sleep restriction
- PubMed 37874350 — Collagen peptide supplementation before bed reduces sleep fragmentation and improves cognitive function in physically active men with sleep complaints
Technical Documents and Supply — Asuka Kimya
You can contact Asuka Kimya for SDS, TDS, CoA, and supply conditions for L-Glycine.
References
The usage, sports nutrition, and health information on this page are compiled from official legislation/institution sources (EFSA, NIH ODS, ISSN, Turkish Food Codex Sports Foods / Dietary Supplements Regulation) and independent scientific publications (PubMed). The product is a food supplement/sports nutrition raw material; it does not claim to diagnose or treat diseases.