Glycine
The simplest amino acid with profound effects on sleep quality, collagen synthesis, and metabolic health
Also known as: L-Glycine • Aminoacetic Acid • Gly
Overview
Glycine is the smallest and simplest amino acid, yet it plays remarkably diverse roles in the body. It's a building block of collagen (33% of collagen is glycine), a precursor to glutathione (the master antioxidant), an inhibitory neurotransmitter that promotes sleep, and a key player in one-carbon metabolism. Clinical research has shown that 3g of glycine before bed significantly improves sleep quality by lowering core body temperature — a critical signal for sleep onset. Glycine is also conditionally essential: the body can synthesize it, but production (3g/day) falls far short of total needs (10-15g/day), creating a chronic deficit that may accelerate aging. Recent research suggests glycine supplementation may extend lifespan by supporting glutathione synthesis and reducing oxidative stress.
Key Benefits
Sleep Quality Improvement
3g glycine before bed significantly improves subjective sleep quality, reduces time to fall asleep, and enhances next-day cognitive performance. The mechanism involves glycine lowering core body temperature by dilating peripheral blood vessels — a key physiological trigger for sleep onset. Unlike sedative sleep aids, glycine doesn't cause morning grogginess.
Collagen Synthesis
Glycine is the most abundant amino acid in collagen, comprising every third residue. Supplemental glycine supports collagen production for skin, joints, tendons, and gut lining. Combined with proline and vitamin C, glycine is a key substrate for collagen synthesis.
Glutathione Production
Glycine is one of three amino acids in glutathione (glycine + cysteine + glutamate). Glycine availability is often the limiting factor in glutathione synthesis, especially in aging. A landmark study found glycine + N-acetylcysteine (GlyNAC) supplementation restored glutathione levels and reversed multiple aging markers in older adults.
Metabolic Health
Glycine improves insulin sensitivity, reduces fasting glucose, and may protect against metabolic syndrome. It's involved in bile acid conjugation (supporting fat digestion) and one-carbon metabolism. Lower plasma glycine levels are consistently associated with type 2 diabetes risk.
Dosage & How to Take
For sleep: 3g before bed. For collagen/glutathione support: 5-10g daily. Glycine has a mildly sweet taste and dissolves easily in water. It's one of the safest amino acids with no known toxicity at supplemental doses.
| Purpose | Dose | Notes |
|---|---|---|
| Sleep improvement | 3 g before bed | 30-60 minutes before sleep. Based on clinical trials. |
| Collagen support | 5-10 g/day | Often combined with vitamin C and proline |
| Glutathione support (GlyNAC) | 1.33 mg/kg/day glycine + NAC | Based on the GlyNAC aging study |
| General health/longevity | 3-5 g/day | Addresses the chronic glycine deficit |
Best Time to Take
For sleep: 30-60 minutes before bed. For other purposes: any time, with or without food.
With or Without Food
Can be taken with or without food. For sleep, take on a relatively empty stomach for faster absorption.
Forms & Bioavailability
| Form | Absorption | Best For | Notes |
|---|---|---|---|
| Free-Form Glycine Powder | High | Flexible dosing, sleep | Mildly sweet taste. Dissolves easily in water. Very affordable. |
| Glycine Capsules | High | Convenience | 3g requires 4-6 capsules. Less convenient than powder for higher doses. |
| Collagen Peptides | High | Glycine + other collagen aminos | Collagen is ~33% glycine. 10g collagen provides ~3.3g glycine plus proline and hydroxyproline. |
Side Effects & Safety
Common
- Very well tolerated
- Mild GI upset at very high doses (>15g)
- Soft stools
Rare
- No significant adverse effects reported in clinical trials
Contraindications
- No known contraindications
- Theoretically, caution with clozapine (glycine may affect NMDA receptor activity)
Interactions
Glycine modulates NMDA receptors; may interact with antipsychotic medications that affect glutamate signaling
Synergistic for glutathione production — the GlyNAC combination restored glutathione and reversed aging markers
Magnesium glycinate provides both glycine and magnesium; complementary for sleep
Scientific Research
Glycine and Sleep Quality
3g glycine before bed improved subjective sleep quality, reduced sleep onset latency, and enhanced next-day cognitive performance without daytime drowsiness
GlyNAC and Aging
Glycine + NAC supplementation for 24 weeks in older adults restored glutathione levels, reduced oxidative stress, and improved mitochondrial function, inflammation, insulin resistance, and physical function
Glycine Thermoregulation
Glycine improves sleep by activating NMDA receptors in the suprachiasmatic nucleus, causing peripheral vasodilation and core body temperature reduction
Food Sources
Frequently Asked Questions
Medical Disclaimer
This content is for educational and informational purposes only and is not intended as medical advice. Always consult with a qualified healthcare professional before starting any supplement regimen, especially if you have pre-existing health conditions or are taking medications. The statements on this page have not been evaluated by the Food and Drug Administration.