Glycine

Your intake

What each level of glycine does

Approximate dose-response bands. Individual response varies — these are starting points, not prescriptions.

1. Severely lowYOU ARE HERE

   0 g – 0.99 g

   Well below target. Risk of deficiency symptoms tied to sleep · collagen.

2. Insufficient

   0.99 g – 3 g

   Below the recommended daily target. Long-term adequacy not assured.

3. Adequate

   3 g – 4.5 g

   Daily target met. Standard nutritional support for sleep · collagen.

4. Therapeutic

   4.5 g – 6 g

   Common for specific health goals. Check the evidence for your situation before sustaining this level.

5. Diminishing returns

   6 g – +

   Past the point where extra intake typically helps. Evidence for further benefit is thin.

Overview

Smallest amino acid; conditionally essential — endogenous synthesis is meaningful but not always sufficient. Substrate for glutathione, creatine, heme, and collagen synthesis. Inhibitory neurotransmitter at glycine receptors and co-agonist at NMDA receptors. Popular evening supplement for sleep quality.

Functions

• ●Substrate for glutathione (GSH) synthesis (with cysteine and glutamate)
• ●Major component of collagen (~33% of residues)
• ●Substrate for creatine, heme, and purine synthesis
• ●Inhibitory neurotransmitter (spinal cord, brainstem)
• ●NMDA receptor co-agonist (glutamate signalling)
• ●Conjugated to bile acids and xenobiotics for excretion

Mechanism

Activates glycine receptors (chloride channels) producing inhibitory postsynaptic potentials, similar to GABA. At NMDA receptors, glycine and D-serine occupy a co-agonist site required for glutamate to activate the channel. In the periphery, glycine lowers core body temperature via thermoregulatory vasodilation — likely the mechanism behind its sleep-onset and sleep-quality benefit.

Benefits

• ●Improves subjective and objective sleep quality at 3 g before bed (small trials)
• ●Modestly raises endogenous glutathione synthesis with cysteine pairing
• ●Improves insulin sensitivity in some metabolic-syndrome studies
• ●Reduces psychotic symptoms when added to antipsychotics in some schizophrenia trials

Deficiency

Frank deficiency is rare but functional shortfall may occur in protein-restricted diets, severe stress, or chronic illness where glycine is consumed faster than synthesised.

Excess

Well-tolerated up to ~30 g/day in studies. No established UL. High oral doses produce only mild GI distress.

Forms

• Plain L-glycine powder
  Cheapest; dissolves easily; mildly sweet — the standard form
• Glycine capsules
  Convenient but pill burden at gram doses
• Magnesium glycinate
  Two-for-one if you want both

Food sources

• Bone broth · 1 cup0.5–2 g
• Pork rinds · 1 oz1.5 g
• Chicken skin (cooked) · 1 oz1.2 g
• Gelatin powder · 1 tbsp2 g
• Cooked salmon · 3 oz1 g
• Beef (cooked) · 3 oz1.2 g

Supplement forms

Plain L-glycine powder is cheap, dissolves easily, and tastes mildly sweet. 3 g 30–60 minutes before bed is the canonical sleep-quality dose. 10–15 g/day in divided doses for glutathione support or metabolic protocols.

Bioavailability

Absorbed efficiently via active transport in small intestine; rapidly available. Taking with food slows absorption modestly. For sleep, the on-empty-stomach taste is mild enough that timing flexibility is high.

Longevity relevance

Glycine adequacy supports glutathione synthesis and connective tissue integrity — both relevant to aging. Recent interest in glycine-NAC combinations (GlyNAC) showing improved markers of mitochondrial function and oxidative stress in older adults; healthspan endpoints pending.

Relationships

References

• Examine — Glycinereview
• Yamadera — glycine improves sleep (Sleep Biol Rhythms 2007)study
• Kumar — GlyNAC supplementation in older adults (J Gerontol 2023)study

About Glycine

Inhibitory neurotransmitter; collagen synthesis, sleep depth, glutathione precursor. Common dose 3 g before bed.

Role

Sleep · collagen

Daily target

3 g (TR)

Also called

glycine, l-glycine