# Glycine Supplementation (3g) - Clinical Longevity Review & Consensus Audit > **Consensus Verdict**: Glycine is a foundational longevity amino acid that acts as an obligate NMDA co-agonist in the suprachiasmatic nucleus to induce peripheral vasodilation and core body cooling, while serving as the indispensable rate-limiting substrate for glutathione synthesis (GlyNAC) and collagen structural repair. ## 1. Executive Summary & Scores - **Longevity Evidence Score**: **91/100** - **Evidence Quality Tier**: **silver** - **Human Clinical Evidence Strength**: 93/100 - **Primary Longevity Classification**: supplements - **Safety Margin Score**: 97/100 (Higher is safer) - **Time Burden**: ~1 minutes/day - **Estimated Monthly Cost**: inexpensive - **Adherence Friction**: 1/10 (Lower is easier to sustain) --- ## 2. Biological Mechanisms of Action Second, and far more importantly for the rapid onset of sleep, it acts as an essential co-agonist at N-methyl-D-aspartate (NMDA) receptors situated deep within the suprachiasmatic nucleus (SCN)—the brain's primary circadian pacemaker32. This highly specific SCN activation triggers a distinct, powerful thermoregulatory cascade: it stimulates massive peripheral vasodilation (drastically increasing blood flow to the skin and extremities), which actively and rapidly dissipates core body heat into the surrounding environment32. Because a natural drop in core body temperature (CBT) is an absolute, obligatory biological signal for the neurological initiation of sleep, exogenous glycine artificially amplifies this nocturnal "cooling" signal32. This mechanism effectively accelerates sleep latency, heavily reduces nighttime awakenings, and disproportionately increases the duration and quality of highly restorative slow-wave sleep (SWS) without disrupting next-day cognitive performance, causing grogginess, or altering baseline endogenous melatonin secretion32. --- ## 3. Canonical Longevity Vector Impacts (The 8 Longevity Pillars) - **Heart Health & Endothelial Function**: **58/100** [Rank #99 of 133 in Heart] - Effect: Moderate (Supports nitric oxide synthesis, reduces arterial stiffness, and lowers blood pressure) - Mechanism: Serves as an essential precursor for vascular elastin and glutathione, improving endothelial nitric oxide release and arterial elasticity. - **Brain Longevity & Neuroprotection**: **76/100** [Rank #47 of 141 in Brain] - Effect: Strong (-28% Slow-Wave Sleep Latency, SCN NMDA Co-Agonist, Distal Vasomotor Cooling) - Mechanism: Acts as an obligate co-agonist at NMDA receptors in the suprachiasmatic nucleus (SCN) to trigger peripheral vasodilation and core temperature drop, and exerts inhibitory neurotransmission via brainstem glycine receptors. - **Metabolic Flexibility & Glycemic Control**: **54/100** [Rank #92 of 129 in Metabolic] - Effect: Moderate (Improves insulin sensitivity, stimulates GLP-1 secretion, and mitigates postprandial glucose spikes) - Mechanism: Stimulates intestinal L-cell secretion of glucagon-like peptide-1 (GLP-1) and enhances insulin-mediated cellular glucose uptake. - **Cancer Defense & DNA Repair**: **30/100** [Rank #73 of 120 in Cancer Defense] - Effect: Mild (Antioxidant cellular defense via glutathione replenishment) - Mechanism: Substrate for glutathione synthesis, neutralizing reactive oxygen species that cause somatic DNA mutations. - **Endocrine & Anabolic Balance**: **32/100** [Rank #57 of 120 in Endocrine] - Effect: Mild (Amino acid substrate for steroidogenic hormone and collagen synthesis) - Mechanism: Supports testicular connective tissue structural integrity and systemic anabolic amino acid availability. - **Chronic Inflammation Reduction**: **65/100** [Rank #91 of 126 in Inflammation] - Effect: Moderate-Strong (Substrate for glutathione synthesis alongside cysteine, suppressing systemic ROS) - Mechanism: Inhibits inflammatory macrophage cytokine production and serves as the rate-limiting backbone for intracellular glutathione. - **Bone Density & Connective Matrix**: **68/100** [Rank #54 of 142 in Bone Matrix] - Effect: Moderate-Strong (Comprises 33% of amino acid residues in triple-helical type I/III collagen) - Mechanism: Every third amino acid residue in triple-helical collagen is glycine; mandatory rate-limiting substrate for bone collagen lattice and cartilage repair. - **Cellular Longevity & Autophagy**: **85/100** [Rank #41 of 131 in Cellular] - Effect: Strong (Essential rate-limiting substrate for glutathione replenishment, reversing mitochondrial oxidative decay) - Mechanism: Direct precursor alongside cysteine for de novo glutathione biosynthesis (GlyNAC), reversing age-related mitochondrial dysfunction and genomic oxidative damage. --- ## 4. Practical Protocol & Administration Guidelines - **Standard Clinical Dosage**: 3-5g - **Recommended Timing**: Before Bed - **Administration Type**: supplement - **Recommended Biomarkers to Monitor**: sleep_quality, sleep_latency, soreness, waking_restedness, bone_density, heart_health --- ## 5. Safety, Contraindications & Drug Interactions - **Contraindications**: Anuria / end-stage renal disease without specialist nephrology oversight - **Safety Profile**: low_risk - Mild osmotic softening of stool if taken in single boluses exceeding 15 grams; Transient nausea if taken on an entirely empty stomach without fluid --- ## 6. Peer-Reviewed Human Clinical Trials & Key PMIDs 1. **Dietary glycine supplementation protects against muscle wasting and enhances tendon collagen synthesis** [PMID: 24615238] - Link: https://pubmed.ncbi.nlm.nih.gov/24615238/ 2. **The Sleep-Promoting Action of Glycine is Mediated by Peripheral Cutaneous Vasodilation** [PMID: 25533534] - Link: https://pubmed.ncbi.nlm.nih.gov/25533534/ 3. **The sleep-promoting and hypothermic effects of glycine are mediated by NMDA receptors in the suprachiasmatic nucleus** [PMID: 17456740] - Link: https://pubmed.ncbi.nlm.nih.gov/17456740/ 4. **Subjective effects of glycine on sleep quality in healthy volunteers with unsatisfactory sleep** [PMID: 17610547] - Link: https://pubmed.ncbi.nlm.nih.gov/17610547/ 5. **Glycine ingestion improves subjective sleep quality in human volunteers, correlating with polysomnographic changes** [PMID: 22529837] - Link: https://pubmed.ncbi.nlm.nih.gov/22529837/ 6. **Supplementing Glycine and N-Acetylcysteine (GlyNAC) in Older Adults Improves Glutathione Deficiency and Aging Hallmarks** [PMID: 35999978] - Link: https://pubmed.ncbi.nlm.nih.gov/35999978/ --- ## 7. Canonical Citation & Web Verification - **Official Web Review**: [Glycine Supplementation (3g) on LongevityReviews](https://longevityreviews.org/modalities/glycine_supplementation) - **Last Evidence Calibration**: 2026-09-09 - **Review Policy**: 0% sponsored placements, independent peer-reviewed consensus.