MikroScore
Science-backed ingredient evidence
Moderate Evidence Safety: Safe Study dose: 3000 mg/day

Glycin

Also known as: Glycine, Aminoessigsäure

Summary Moderate Evidence

Glycine is the smallest amino acid, required for glutathione, collagen, and creatine. In GlyNAC form, it shows promise for aging markers in older adults.

EU Health Claims: No approved claims

No approved EFSA health claims for glycine as a supplement. As an amino acid, it is freely available as a dietary supplement in the EU. In medicine, glycine infusions are used in prostate surgery.

AI Summary

Quick verdict

Glycine is the smallest amino acid, required for glutathione, collagen, and creatine. In GlyNAC form, it shows promise for aging markers in older adults.

What the evidence supports

Well-documented effect on sleep quality (RCT). As GlyNAC combined with NAC, smaller RCTs show significant improvements in glutathione status, oxidative stress, and mitochondrial function in older adults.

What is NOT supported

Long-term safety and rare adverse effects in humans remain insufficiently studied.

EU/EFSA status

Not approved. No approved EFSA health claims for glycine as a supplement. As an amino acid, it is freely availa…

Safety

Safe

This AI summary is generated from the structured data on this page.

What Is Glycine?

Glycine is the smallest and simplest of all protein amino acids. Your body can synthesize it endogenously, but research suggests that self-produced glycine becomes insufficient with age to meet physiological demand.

Glycine participates in a surprisingly diverse array of essential metabolic processes:

  • Glutathione synthesis: Together with cysteine and glutamic acid—glycine deficiency represents a rate-limiting bottleneck in older adults
  • Collagen synthesis: Every third amino acid in collagen is glycine; critical for skin, joints, and connective tissue
  • Creatine synthesis: Produced together with arginine and methionine; essential for muscle energy metabolism
  • Hemoglobin formation: A structural component of the porphyrin ring system
  • Neurotransmission: Functions as an inhibitory neurotransmitter in the spinal cord and brainstem; may promote sleep through core body temperature reduction

Its small size and simple structure belie its metabolic importance. Serum glycine concentration naturally declines with age in humans, correlating with reduced hepatic synthesis and increased peripheral tissue demand. This may explain why aging tissues show accelerating signs of collagen degradation, mitochondrial dysfunction, and antioxidant insufficiency.

The GlyNAC Approach: Targeting Glutathione Deficiency

The most compelling healthy-aging application is combining glycine with NAC (N-acetylcysteine). Both amino acids are precursors of glutathione (GSH)—arguably the body’s most important antioxidant and cellular detoxification molecule. Glycine provides one of three structural components (the glycyl residue); NAC supplies cysteine (the reactive thiol group); glutamic acid is added enzymatically by the enzyme glutathione synthetase.

Plasma glutathione concentration declines by approximately 30–50% from age 20 to age 60, particularly in cells with high metabolic and oxidative demand. This depletion correlates with increased oxidative stress, mitochondrial dysfunction, impaired detoxification, and accelerated aging phenotypes.

Clinical Evidence: The Baylor GlyNAC Trials

Rajagopal Sekhar’s research group at Baylor University conducted two randomized controlled trials in healthy older adults:

Study Design: Adults aged 60+ years (BMI 25–32 kg/m²), randomized to either GlyNAC (1.33 g glycine + 1 g NAC daily) or placebo for 24 weeks. Stratified randomization; outcomes were pre-specified.

Key Results (2021 trial, n=24):

  • Plasma glutathione normalized to young-adult (age 20–30) levels within 12 weeks and remained elevated through week 24
  • Markers of oxidative stress (plasma F2-isoprostanes, a lipid peroxidation marker) decreased by approximately 30%
  • Inflammatory markers (TNF-α, IL-6) showed modest but measurable improvements
  • Insulin sensitivity (HOMA-IR index) improved
  • Mitochondrial hydrogen peroxide emission (measured via specialized respirometry) decreased significantly—indicating reduced intramitochondrial oxidative stress
  • Body composition improved: fat mass decreased, lean mass increased
  • Walking speed increased by approximately 0.1 m/s (clinically meaningful in older adults; 0.05–0.1 m/s change predicts mortality)
  • Grip strength improved modestly but significantly

The 2022 follow-up trial (n=43, 24 weeks) replicated and extended these findings, showing improvements in 8 of 9 measured hallmarks of aging.

Critical Limitations: Small sample sizes (n=24–43), single-center trials from a single research group, 24-week duration only. No long-term follow-up beyond 6 months. Independent replication trials are underway but not yet published. The magnitude of biological benefit requires confirmation before broad clinical recommendation; however, the consistency of biomarker changes is encouraging.

Sleep: One of the Best-Documented Supplement Effects

Glycine has perhaps the strongest evidence base for any supplement effect on sleep—not because of enormous effect sizes, but because the mechanism is biologically plausible, human data are consistent, and the effect is dose-dependent.

Dosing Protocol: 3 g glycine, dissolved in water or a light beverage, consumed 30 minutes before bedtime

Observed Effects:

  • Shortened sleep latency (time to fall asleep) by approximately 10–15 minutes
  • Polysomnography confirmed improved sleep architecture: increased slow-wave sleep (deep sleep), higher sleep efficiency, fewer arousals
  • Reduced next-day fatigue and daytime somnolence (measured with validated fatigue scales like the Fatigue Assessment Scale)
  • No rebound insomnia or tolerance development upon discontinuation
  • Effect develops over 3–5 nights; cumulative over 1–2 weeks

Proposed Mechanism: Glycine causes peripheral vasodilation—widening of blood vessels in skin and extremities—thereby lowering core body temperature. Core body temperature drop is a fundamental circadian sleep trigger; thermoreceptors in the preoptic anterior hypothalamus (the body’s thermostat) detect this change and promote sleep onset. Additionally, glycine binds to spinal and brainstem glycine receptors (part of inhibitory neurotransmission), suppressing arousal-promoting neural pathways.

Evidence Quality: Multiple small randomized controlled trials (n = 11–18), consistent direction of effect, dose-response relationship, plausible mechanism confirmed in human PET and animal studies. Meta-analyses support efficacy. Effect sizes are modest but clinically meaningful for older adults or individuals with sleep-onset insomnia.

Safety and Tolerability

Glycine is used clinically at very high intravenous doses (up to 1–1.5 g/kg body weight) during transurethral resection of the prostate (TURP) and other surgical procedures. Oral glycine is considered safe at doses up to 10–20 g daily in humans; no serious adverse events have been reported in the scientific literature.

  • Gastrointestinal effects: Well tolerated; no significant GI disturbances at 3–10 g daily. Sweet taste is mild, easily masked in beverages
  • Drug interactions: None documented; glycine is an endogenous amino acid
  • Long-term safety: Limited long-term data available, but no safety signals in published trials
  • Contraindications: None identified in humans; theoretical concern in schizophrenia (glycine is thought to be hyperactive in this condition), but no clinical evidence of harm
  • Pregnancy/Lactation: Insufficient data; conservative approach is to avoid high-dose supplementation

Practical Recommendations

Glycine is inexpensive (typically €0.08–0.15 per gram), demonstrably safe, and supported by solid evidence for sleep optimization and as a component of age-targeted strategies.

For sleep optimization: 3 g glycine, 30 minutes before bed, on an empty stomach or after a light meal. Allow 3–5 nights for full effect to manifest.

For GlyNAC-based aging support: 1.33 g glycine combined with 1 g NAC daily, divided into morning and evening doses. This ratio reflects the stoichiometry of glutathione synthesis. Expect 8–12 weeks before biomarker changes become apparent. Plasma glutathione can be measured in specialized reference labs (HPLC-based assays) if you wish to track response; most general practitioners are unfamiliar with this measurement.

Timing: For sleep, glycine works optimally when core body temperature naturally begins to drop (evening). For GlyNAC, consistency matters more than timing of doses.

Expected timeline: Sleep effects within 1 week; GlyNAC biomarker changes within 8–12 weeks. Sustained use is required; benefits decline upon discontinuation.

Key Studies

The effects of glycine on subjective daytime performance in partially sleep-restricted healthy volunteers

Bannai M et al. (2012)

RCT (n=11): 3 g glycine before sleep was associated with improvements in sleep quality, daytime fatigue, and next-morning cognitive function (polysomnography-confirmed).

PubMed PMID 22529837

Supplementing Glycine and N-Acetylcysteine (GlyNAC) in Older Adults Improves Glutathione Deficiency, Oxidative Stress, Mitochondrial Dysfunction, Inflammation, Physical Function, and Aging Hallmarks: A Randomized Clinical Trial

Sekhar RV (2022) n=12

Follow-up RCT: GlyNAC was associated with improvements in 8 of 9 measured hallmarks of aging, including oxidative stress, inflammation, mitochondrial function, body composition, muscle strength, and gait speed.

PubMed PMID 35975308

Glycine metabolism in animals and humans: implications for nutrition and health

Razak MA et al. (2017)

Review: Glycine is required for glutathione, collagen, hemoglobin, creatine, and porphyrins—daily physiological requirements exceed endogenous synthesis capacity from midlife onward.

PubMed PMID 28759885
Editorial notice: For most ingredients described here, no health claims are approved in the EU (Regulation (EC) 1924/2006). Evidence levels are editorial assessments of research quality — not health promises. This content is not a substitute for medical advice and does not constitute a recommendation to treat, alleviate, or prevent any disease.