Glycine
Evidence Fact Sheet
Glycine is the simplest amino acid, acting as an inhibitory neurotransmitter and NMDA-receptor co-agonist, a glutathione-synthesis precursor, and a major collagen building block. It is a permitted dietary-supplement amino acid (FDA GRAS, EU 2002/46/EC, ANVISA, China GB 2760) with no ingredient-specific authorized health claims; human evidence is emerging, with the strongest aging signal coming from glycine+NAC combinations rather than glycine alone.
Also known as: Glycine · Aminoacetic acid · L-Glycine · Gly
Overview
Glycine is the smallest amino acid and is conditionally essential in humans. Mechanistically it works as an inhibitory neurotransmitter and a co-agonist at the NMDA receptor's glycine site (linked in research to core-temperature drop and sleep onset), as a rate-contributing precursor for glutathione synthesis, and as a substrate making up roughly one third of collagen residues. Research doses typically span about 3 g/day before bed in sleep studies and 3-5 g/day in metabolic studies, with aging-focused trials using glycine combined with N-acetylcysteine (GlyNAC) at higher weight-based amounts; the US market median is around 1000 mg/day. Regulatory status is that of a permitted amino-acid food/supplement ingredient (FDA GRAS under 21 CFR 172.320, EU Directive 2002/46/EC Annex I, ANVISA RDC 243/2018, China GB 2760) with structure/function language only and zero glycine-specific authorized functional claims. This page reports research findings in studied populations and is educational, not a dosing recommendation or medical advice.
Mechanism of Action
Inhibitory neurotransmitter + NMDA co-agonist (linked to core-body-temperature drop and sleep onset in research) · Glutathione synthesis precursor amino acid · Collagen synthesis substrate (~1/3 of collagen residues)
Body systems: Sleep-Wake System · Neurological & Cognitive · Mitochondrial & Cellular Energy · Skin & Connective Tissue
Evidence-Based Benefits
Each benefit below is anchored to a specific PubMed-indexed study. Effect sizes, sample sizes, and p-values are reported as published; no values are inferred. Honest negatives and null results are kept alongside the positive findings, and disease-research populations are described as such — Glycine is not characterized as a treatment for any disease.
Sleep & Nervous System (Research Overview)
Meta-analysis supported- 18 + 34 studieshealthy + diseased cohorts
- up to 14 days / 4 monthsdurations · healthy / diseased
- high risk of biassleep evidence caveat
A 2024 systematic review summarizing glycine administration across eleven physiological systems in adult humans found the nervous system showed the most positive effects, and longer-term glycine improved sleep in healthy populations. Importantly, the authors flagged that these sleep studies had small sample sizes with a high risk of bias, and called for larger, more robust trials.
Reported effect: Glycine administered to healthy and diseased populations (18 and 34 studies) for up to 14 days and 4 months respectively; nervous system showed the most positive effects; sleep improved in healthy populations but with small samples and high risk of bias.
“Glycine was administered to healthy and diseased populations (18 and 34 studies) for up to 14 days and 4 months, respectively. The nervous system demonstrated the most positive effects, including improved psychiatric symptoms from longer-term glycine administration in psychiatric populations. While longer-term glycine administration improved sleep in healthy populations, these studies had small sample sizes with a high risk of bias.”
Source: PMID 37851316 · Soh 2024 · GeroScience
Memory & Attention (Cognition RCT)
RCT supported- improved retrievalepisodic memory · both groups
In a double-blind, randomized, crossover study, a bioactive glycine form (Bioglycin) significantly improved retrieval from episodic memory in both young and middle-aged adults. Honest partial negative: it did not affect focused or divided attention, and had no stimulant or mood effects — it primarily improved memory rather than attention.
Reported effect: Bioglycin significantly improved retrieval from episodic memory in both the young and the middle-aged groups, but it did not affect focused or divided attention; middle-aged men benefited in the sustained-attention task.
“Bioglycin significantly improved retrieval from episodic memory in both the young and the middle-aged groups, but it did not affect focused or divided attention. However, the middle-aged men significantly benefited from Bioglycin in the sustained-attention task.”
Source: PMID 10587285 · File 1999 · J Clin Psychopharmacol
Glutathione & Healthy-Aging (GlyNAC Combination)
RCT supported- 24 older + 12 youngadults studied
- 16 weekssupplementation · older adults
- N=12 vs N=12GlyNAC vs placebo
A placebo-controlled randomized clinical trial gave older adults GlyNAC (glycine combined with N-acetylcysteine) for 16 weeks. GlyNAC, and not placebo, improved or corrected glutathione deficiency, oxidative stress, mitochondrial dysfunction, inflammation, insulin resistance, physical function and several aging hallmarks. Key caveat: this is the glycine+NAC combination, not glycine alone, in a small sample.
Reported effect: Twenty-four older adults and 12 young adults studied; older adults randomized to GlyNAC (N=12) or isonitrogenous alanine placebo (N=12) for 16 weeks; GlyNAC (and not placebo) improved/corrected the measured defects.
“Twenty-four OA and 12 young adults (YA) were studied. OA was randomized to receive either GlyNAC (N = 12) or isonitrogenous alanine placebo (N = 12) for 16-weeks... GlyNAC (and not placebo) supplementation in OA improved/corrected these defects.”
Source: PMID 35975308 · Kumar 2023 · J Gerontol A Biol Sci Med Sci
Coronary Heart Disease & Type 2 Diabetes (Mendelian Randomization)
Null / no benefit Meta-analysis supported- 80,003 participantsGWAS meta-analysis
- 27 genetic loci22 newly reported
- weaker for T2Ddiabetes association
A genome-wide meta-analysis in 80,003 participants used genetic approaches to test whether glycine causally lowers cardio-metabolic risk. It found glycine genetically associated with lower coronary heart disease risk (possibly partly via blood pressure). Honest negative: evidence for a genetic association with type 2 diabetes was weaker, and the glycine-T2D link appeared driven by insulin resistance lowering glycine rather than the reverse.
Reported effect: Meta-analysis of GWAS for glycine in 80,003 participants; 27 genetic loci (22 newly reported); glycine genetically associated with lower CHD risk, partly via blood pressure; evidence for genetic association with T2D was weaker.
“We present a meta-analysis of genome-wide association studies for glycine in 80,003 participants... We identify 27 genetic loci, of which 22 have not previously been reported for glycine. We show that glycine is genetically associated with lower CHD risk and find that this may be partly driven by blood pressure. Evidence for a genetic association of glycine with T2D is weaker, but we find a strong inverse genetic effect of hyperinsulinaemia on glycine.”
Source: PMID 30837465 · Wittemans 2019 · Nat Commun
Metabolic Markers in Severe Obesity (Clinical Study)
RCT supported- 19 participantssevere obesity
- 100 mg/kg/day · 2 weeksglycine dose
In a clinical study, 19 participants with severe obesity took dietary glycine at 100 mg/kg/day for two weeks. There were no changes in body weight, but significant reductions in plasma triglyceride and aminotransferases (liver enzymes), alongside increased plasma glycine. Effect-size magnitudes were not reported numerically in the abstract, so this is a directional finding in a small sample.
Effect size: this study reports the direction of the finding but does not state a specific numeric effect size, so none is given here rather than estimated.
“19 participants with severe obesity (BMI 38.3 ± 5.3 kg/m²) were treated with dietary glycine (100 mg/kg/day) for two weeks... There were no changes in body weight but significant reductions in plasma triglyceride and aminotransferases.”
Source: PMID 41107432 · Tan 2025 · Sci Rep
Dosage (research context · not a recommendation)
3 g/day before bed in sleep research; 3-5 g/day in metabolic studies; GlyNAC aging research used ~100 mg/kg/day glycine combined with NAC. US market median ~1000 mg/day. Educational reference, not a dosing recommendation.
Regulatory Status · 4 Markets
- US · FDA
- GRAS by direct listing under 21 CFR 172.320 (amino acids added to foods); pre-1994 Old Dietary Ingredient under DSHEA; marketed as a dietary supplement with structure/function claims only
- EU · EFSA
- Authorized food-supplement amino acid under Directive 2002/46/EC Annex I; 0 glycine-specific authorized health claims (general structure/function language only)
- CN · China
- China: amino-acid nutritional fortifier / food additive under GB 2760, usable in health-food and general-food formulas; no glycine-specific health-food functional claim approved.
- BR · ANVISA
- Permitted dietary-supplement amino-acid raw material (RDC 243/2018 / IN 28/2018); no glycine-specific Anexo V functional claim
Safety
Well tolerated at 3-5 g/day in human studies; schizophrenia research used up to 60 g/day without serious adverse events; no official upper limit. High doses over 10 g occasionally linked to mild GI discomfort or drowsiness. Caution with clozapine (possible reduced efficacy); inadequate pregnancy/lactation data. Educational, not medical advice.
Related
Goals: cognitive-support · longevity-stack
Lifestyles: high-stress
References
PubMed-indexed citations anchoring the benefit findings above. Effect sizes are reported as published.
- PMID 37851316 · Soh 2024 · GeroScience — Sleep & Nervous System (Research Overview)
- PMID 10587285 · File 1999 · J Clin Psychopharmacol — Memory & Attention (Cognition RCT)
- PMID 35975308 · Kumar 2023 · J Gerontol A Biol Sci Med Sci — Glutathione & Healthy-Aging (GlyNAC Combination)
- PMID 30837465 · Wittemans 2019 · Nat Commun — Coronary Heart Disease & Type 2 Diabetes (Mendelian Randomization)
- PMID 41107432 · Tan 2025 · Sci Rep — Metabolic Markers in Severe Obesity (Clinical Study)
Frequently Asked Questions
1. What is glycine and how is it thought to work?
Glycine is the simplest amino acid and is conditionally essential. Research describes three main mechanisms: it acts as an inhibitory neurotransmitter and a co-agonist at the NMDA receptor's glycine site (linked to core-temperature drop and sleep onset), it serves as a precursor for glutathione synthesis, and it is a substrate making up roughly one third of collagen residues. This page reports research findings in studied populations and is not medical advice.
2. Does glycine actually improve sleep or memory in humans?
The human evidence is emerging rather than settled. A 2024 GeroScience systematic review (Soh 2024) found the nervous system showed the most positive effects and that longer-term glycine improved sleep in healthy populations, but cautioned those sleep studies had small samples and a high risk of bias. For cognition, a randomized crossover trial (File 1999) found glycine significantly improved episodic-memory retrieval but did not affect focused or divided attention.
3. Is the anti-aging evidence about glycine alone or glycine plus NAC?
The strongest aging signal comes from GlyNAC — glycine combined with N-acetylcysteine — not glycine on its own. In a randomized clinical trial (Kumar 2023), 24 older adults plus 12 young adults were studied and 16 weeks of GlyNAC (not placebo) improved glutathione, oxidative stress, mitochondrial function, inflammation and physical function. Because this is a combination in a small sample, single-ingredient glycine evidence remains thinner.
4. What does the research say about glycine and heart or metabolic health?
A genome-wide meta-analysis in 80,003 participants (Wittemans 2019) found glycine genetically associated with lower coronary heart disease risk, possibly partly via blood pressure, while the association with type 2 diabetes was weaker. In a separate small clinical study of 19 people with severe obesity (Tan 2025), glycine at 100 mg/kg/day for two weeks produced no weight change but significant reductions in plasma triglyceride and aminotransferases.
Last evidence review: 2026-06-13