Glycine
Research Reliability -
A simple amino acid with outsized effects on sleep quality, glutathione production, and core body temperature.
Appetite
Mood
Sleep
Glycine
Description
Glycine is the smallest amino acid but a major substrate for glutathione (the body's master antioxidant) and collagen synthesis, while also acting as an inhibitory neurotransmitter in the spinal cord and brainstem. Taken before bed, clinical studies show it lowers core body temperature slightly and improves subjective sleep quality and next-day cognitive performance, likely via this neurotransmitter action combined with peripheral vasodilation. It is also a popular addition to longevity stacks as a counterbalance to methionine-heavy diets, since glycine consumes one-carbon units in a way that may offset some pro-aging methionine signaling.
Effects
First night
calmer, cooler, easier sleep onset for many
Same night
Weeks
How It Feels
Taken before bed, many feel a genuinely easier, more restful sleep and wake less groggy, partly because glycine gently lowers core body temperature. It tastes pleasantly sweet and mixes easily. The longer-term collagen and metabolic benefits are quiet and slow.
Evidence
Evidence Strength
Preliminary (limited / small human data)
Caveats
Sleep-quality evidence comes from a small number of modestly sized trials, several from the same research group.
Usage
Commonly Referenced Starting Amount
1 g/day
Commonly Referenced Amount
3 g before bed is the dose used in most sleep-quality research; some studies go to 15–30 g
Referenced Upper Limit
No upper limit has been established
Onset
Same night (sleep); weeks (collagen/methylation)
Biomarkers to Track
Subjective
(Daily)
Sleep onset time and quality
Morning grogginess
Skin and joint comfort
Objective
(Quarterly)
Sleep tracker deep sleep percentage
Plasma glycine level (specialty)
hs-CRP
Very safe and well tolerated, with a pleasant sweet taste.
Almost no one, though those on clozapine should note an interaction.
Underdosing it for sleep, when 3 grams before bed is the studied amount.
Disclaimer
This information is for educational purposes only and is not medical advice. It is not intended to diagnose, treat, cure, or prevent any disease. Consult a qualified healthcare provider before starting any new supplement, especially if you are pregnant, nursing, taking medication, or managing a health condition.
Kawai N et al. (2015). Frontiers in Neurology. Review (glycine and sleep quality). PMID: 26557105.
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