Benefits
Improved Sleep Quality
Glycine may enhance sleep by reducing core body temperature and calming the nervous system. Studies suggest 3 grams taken before bed can improve sleep onset and quality, reducing daytime fatigue.
Cognitive and Mood Support
Glycine acts as a neurotransmitter and may improve memory, attention, and mood. It’s involved in NMDA receptor function, which supports learning and memory. Some evidence links glycine to reduced symptoms of depression and anxiety.
Collagen and Joint Health
Glycine is a key component of collagen, supporting skin, joint, and connective tissue health. Supplementation may aid tissue repair and reduce joint pain, particularly in conditions like osteoarthritis.
Metabolic Health
Glycine may improve insulin sensitivity and reduce inflammation, potentially lowering the risk of metabolic disorders. It’s been studied for its role in managing blood sugar and protecting against oxidative stress.
Liver Protection
Glycine may support liver function by aiding detoxification and reducing damage from alcohol or toxins. It’s shown promise in animal studies for protecting against liver injury.
Muscle Preservation
Glycine may help prevent muscle wasting, especially in conditions like sarcopenia or during caloric restriction, by supporting protein synthesis.
Mechanism of action
Neurotransmitter Role
Glycine is an inhibitory neurotransmitter in the central nervous system, acting on glycine receptors to hyperpolarize neurons, reducing neuronal excitability and promoting calmness.
Thermoregulation
Glycine lowers core body temperature by increasing cutaneous blood flow, facilitating sleep onset. It interacts with NMDA receptors in the suprachiasmatic nucleus (regulating circadian rhythms).
NMDA Receptor Modulation
Glycine is a co-agonist at NMDA receptors, enhancing glutamatergic signaling critical for synaptic plasticity, learning, and memory.
GABAergic Effects
Its inhibitory action on glycine receptors reduces overexcitation, potentially alleviating anxiety and depression symptoms.
Collagen Synthesis
Glycine is a primary amino acid in collagen (about 33% of collagen’s structure), providing structural support for connective tissues, skin, and joints.
Anti-inflammatory Effects
Glycine inhibits pro-inflammatory cytokines (e.g., TNF-α, IL-6), reducing joint inflammation and supporting tissue repair.
Insulin Sensitivity
Glycine enhances insulin signaling, possibly by improving glutathione synthesis, which reduces oxidative stress and supports glucose uptake.
Anti-inflammatory
It inhibits NF-κB activation, reducing systemic inflammation linked to metabolic disorders.
Detoxification
Glycine is a precursor to glutathione, a key antioxidant that neutralizes reactive oxygen species and supports liver detoxification.
Cytoprotection
It reduces oxidative damage and inflammation in hepatocytes, protecting against alcohol- or toxin-induced liver injury.
Protein Synthesis
Glycine supports mTOR signaling and provides building blocks for muscle protein synthesis, counteracting muscle breakdown.
Anti-catabolic
It reduces muscle degradation by inhibiting inflammatory pathways and oxidative stress.
Clinical trials
Randomized, placebo-controlled trial in 24 older adults (mean age 65) and 12 young adults receiving GlyNAC (glycine 1.33 mmol/kg/day + NAC 0.81 mmol/kg/day) for 16 weeks. Outcomes: glutathione, oxidative stress, mitochondrial dysfunction markers, body composition, multi-system function. (Nutrients)
24 older adults + 12 young adult comparators. 16-week intervention.
GlyNAC improved or normalized: glutathione levels, oxidative stress markers, mitochondrial dysfunction, inflammation, insulin resistance, endothelial function, gait speed, cognition, body composition. Multiple aging hallmarks improved. Note: small sample, single research group (Sekhar lab at Baylor); independent replication needed. Promising but preliminary evidence for an emerging anti-aging intervention.
Open-label, controlled trial in 56 patients with severe COVID-19 requiring mechanical ventilation receiving enteral glycine vs standard care. Outcomes: clinical recovery, ICU outcomes, mortality. (2024 Mexican trial)
56 severe COVID-19 ICU patients.
Primary endpoint negative: enteral glycine did not improve major clinical outcomes (mortality, ventilator-free days, ICU LOS) in severe COVID-19. Negative finding important — extrapolating GlyNAC anti-aging signals to acute critical illness was not supported.
Randomized controlled trial in 114 healthy older adults (mean age 65) receiving GlyNAC at low (2.4 g/day), medium (4.8 g/day), or high (7.2 g/day) doses for 12 weeks. Outcomes: glutathione, biomarkers, tolerability. (2022)
114 healthy older adults. 12-week dose-finding.
Dose-dependent glutathione elevation; higher doses produced more robust biomarker improvements. Generally well-tolerated across doses. Adds dose-response data to the GlyNAC research program.
Pilot clinical trial in children with cystic fibrosis receiving oral glycine vs placebo for 8 weeks. Outcomes: clinical status, spirometry (FEV1), inflammatory markers. (2017)
Children with CF (small pilot).
Modest improvements in inflammatory markers vs placebo; minimal effect on lung function. Pilot study; not established CF intervention. Modern CF management has been transformed by CFTR modulators (elexacaftor-tezacaftor-ivacaftor / Trikafta®) — supplemental glycine should not be considered comparable.
Double-blind, placebo-controlled crossover trial in 22 patients with treatment-resistant schizophrenia receiving high-dose glycine (0.4-0.8 g/kg/day, ~30-60 g for 75 kg adult) as adjuvant to antipsychotics. Outcomes: PANSS, negative symptoms. (Heresco-, Biol Psychiatry — or related work)
22 treatment-resistant schizophrenia patients. Crossover.
High-dose glycine reduced negative symptoms (avolition, blunted affect) vs placebo. Mechanism: NMDA glycine modulatory site agonism. Critical context: this finding has been replicated with mixed results; large definitive Phase 3 trials of glycinergic agents (sarcosine, glycine) for schizophrenia have been less impressive. CATIE-style trials of D-cycloserine (related mechanism) were negative. Modern schizophrenia treatment has not adopted high-dose glycine. Doses required are very large (30-60 g/day) — challenging for compliance.
3-year observational study in 127 volunteers prone to frequent viral infections. 85 received glycine 10 g/day; 42 controls. Outcomes: infection frequency. (2020 observational)
127 volunteers, observational design.
Glycine group reported fewer viral infections than controls. Critical caveat: not a randomized trial — observational; selection effects and recall bias likely. Evidence is weak. Should not be cited as established viral prevention.
Animal study in rats with colorectal liver metastasis evaluating glycine alone or with FOLFOX chemotherapy. Outcomes: tumor volume, vascularization. (2020)
Rats — animal model, not clinical trial.
Glycine reduced tumor volume and vascularization in this animal model. Critical caveat: animal research — does not establish clinical relevance. Many cancer-relevant findings in animal models have not translated to human cancer treatment. Cancer patients should consult their oncologist before any supplementation; some supplements interfere with chemotherapy.