Glycine — Supplements
Simplest amino acid with PSG-confirmed sleep quality improvement, glycemic benefits, and collagen synthesis support at 3 g before bed.
Overview
Glycine is the simplest amino acid and a conditionally essential neurotransmitter, serving as both an inhibitory neurotransmitter (glycine receptors in the spinal cord and brainstem) and a co-agonist at NMDA glutamate receptors. As a supplement (3 g taken 1 hour before bed), glycine has demonstrated significant sleep quality improvement in multiple Japanese RCTs using polysomnography (PSG) — the gold standard for sleep assessment. Glycine reduces core body temperature through peripheral vasodilation (a mechanism shared with melatonin), accelerates slow-wave sleep (SWS) onset, reduces sleep onset latency, and improves next-day alertness and fatigue on validated scales. A 2025 narrative review in Nutrition Reviews confirmed glycine and L-theanine as the two amino acids with the most promising sleep-promoting properties based on PSG-confirmed evidence. Beyond sleep, glycine is a critical substrate for collagen synthesis (every third residue in collagen triple helix), glutathione production, creatine biosynthesis, and heme synthesis. Recent evidence also suggests glycine improves insulin sensitivity and reduces glycine deficiency common in metabolic syndrome and T2DM.
Indications
- Sleep quality improvement and sleep onset latency reduction
- Daytime fatigue and performance after poor sleep
- Collagen synthesis support (joint, skin, connective tissue)
- Glycine deficiency in metabolic syndrome and type 2 diabetes
- Adjunctive support for schizophrenia (high-dose, co-treatment with antipsychotics)
Mechanism of Action
Glycine acts on NMDA receptors and glycine receptors in the hypothalamus and spinal cord, inducing peripheral vasodilation that accelerates distal heat loss — the primary physiological trigger for sleep onset (core temperature drop)
Dosing
| Compound | Dose | Frequency | Notes |
|---|---|---|---|
| Glycine (free-form amino acid) | 3 g | Once, 1 hour before bed | Dose used in all PSG-confirmed sleep RCTs; pleasant sweet taste makes compliance high |
| Glycine (collagen support) | 5–10 g | Once daily, any time | Higher doses for collagen synthesis; often obtained via collagen peptides (3g glycine per 10g collagen) |
Safety & Contraindications
- Excellent safety profile — no adverse effects reported in clinical trials at 3–15 g/day
- Mild GI discomfort possible at high doses (>15 g/day) — nausea, soft stools
- High-dose glycine (>30 g/day) used adjunctively in schizophrenia was well tolerated in trials
- No known drug interactions at supplement doses
- Not a CNS depressant — does not cause sedation or cognitive impairment (unlike benzodiazepines); alertness improved in morning after use
- Safe for long-term use; endogenous production ~3 g/day from serine, choline, threonine, hydroxyproline