If you’ve ever taken a sleep supplement, chances are you’ve tried melatonin, magnesium, or perhaps valerian or L-theanine. But there is an amino acid that costs pennies per dose, tastes sweet enough to use as a sugar substitute, and has a sleep mechanism that works through a distinctive pathway — yet almost nobody knows about it.
That amino acid is glycine. The smallest and simplest amino acid in nature, it was discovered in 1820 and was quickly classified as “non-essential” because the body can synthesize it from serine. That classification stuck for nearly 200 years, and emerging research suggests it may be incomplete.
The Suprachiasmatic Nucleus Mechanism
The sleep story begins with a research team at Ajinomoto and Stanford University’s Sleep and Circadian Neurobiology Laboratory. In a 2015 paper published in Neuropsychopharmacology, Kawai and colleagues used a rat model to investigate a mechanism by which glycine may promote sleep.1
• The pathway is specific and well-characterized — Oral glycine can cross the blood-brain barrier and reach the suprachiasmatic nucleus (SCN), the brain’s master circadian clock. There, it binds to the glycine co-agonist site on N-methyl-D-aspartate (NMDA) receptors in the SCN shell.
• This process initiates heat loss to support sleep onset — It activates neurons that trigger peripheral vasodilation, a condition wherein blood vessels in your hands and feet dilate, radiating heat away from your core. As core body temperature drops, non-rapid eye movement (NREM) sleep onset is initiated.
• The researchers tested this through a series of experiments — When they ablated the SCN entirely, glycine’s sleep effects were completely abolished. When they blocked NMDA receptors with antagonists, the vasodilation stopped. But when they blocked glycine receptors with strychnine, there was no effect. These findings suggest the mechanism operates primarily through NMDA receptors in the SCN.
Human Sleep Trial Evidence
In human trials, 3 grams of glycine taken before bedtime improved subjective sleep quality and reduced next-day fatigue in volunteers with restricted sleep.2 An earlier review from the same group explored glycine as a potential approach to supporting sleep quality, showing it decreased core body temperature and induced improvements in both subjective and objective sleep quality.3
• Higher doses delivered through collagen peptides also improved sleep continuity — A 2024 randomized crossover study involving 13 physically active men with sleep complaints found that 15 grams of glycine-rich collagen peptides before bedtime reduced sleep awakenings and improved cognitive function the next morning. The study, conducted in partnership with a collagen peptide manufacturer, did not find effects on sleep quantity, latency, or efficiency.4
• Objective sleep measurements indicated fewer nighttime awakenings — The study used polysomnography to record fewer awakenings compared to placebo. This is notable because it suggests the sleep effect may scale with dose and persist even when glycine is delivered as part of a collagen peptide matrix rather than as free glycine alone.
• Glycine’s mechanism of action differs from that of other sleep aids — Rather than directly modulating circadian signaling like melatonin or acting on GABA receptors like GABAergic sedatives, glycine appears to work through thermoregulation, mimicking the natural drop in core body temperature that your body uses to initiate sleep. It also promotes physiological sleep architecture without altering brain wave patterns or causing rebound effects.
The 2015 Kawai paper suggested that glycine’s effects may be mediated primarily through the SCN — the body’s own circadian pacemaker — meaning it works with the clock rather than overriding it.
The Glutathione Connection
Glycine’s benefits extend far beyond sleep. It is the rate-limiting substrate for glutathione synthesis. Glutathione — a tripeptide made from glycine, cysteine, and glutamic acid — is the most abundant intracellular antioxidant in the human body. When glycine levels are insufficient, glutathione production may be compromised.
This is what Dr. Rajagopal Sekhar’s group at Baylor College of Medicine has investigated in a series of studies on glycine combined with N-acetylcysteine (GlyNAC), providing the two rate-limiting precursors for glutathione synthesis.
The Baylor GlyNAC Trial — Addressing Aging Hallmarks
In a 2023 randomized, placebo-controlled clinical trial involving 24 older adults, 16 weeks of GlyNAC supplementation was associated with improvements in glutathione levels, oxidative stress markers, mitochondrial function, inflammation, insulin resistance, endothelial function, gait speed, muscle strength, and several molecular hallmarks of aging.5
• The study examined multiple endpoints simultaneously — This was not a single-endpoint study. It addressed oxidative stress, mitochondrial dysfunction, inflammation, insulin resistance, endothelial dysfunction, genomic damage, physical function, and body composition simultaneously.
• An earlier 36-week open-label pilot study reported additional findings — The study involved eight older adults and eight younger adults as a baseline comparison group.
After 24 weeks of supplementation, older adults were reported to show improvements in glutathione levels, mitochondrial fuel oxidation, inflammation, endothelial function, insulin resistance, cognition, muscle strength, exercise capacity, body fat, and waist circumference.6 Though, as a small pilot study, these findings would need confirmation in larger controlled trials.
• When supplementation was withdrawn in the pilot study for 12 weeks, the benefits declined — This suggested that maintaining adequate glycine may require ongoing intake. This is consistent with the Meléndez-Hevia model, which proposes that the deficit is permanent and biochemical, not a one-time problem that can be fixed and forgotten.
Independent Validation and Dose-Response
Sekhar’s comprehensive 2021 review presented evidence suggesting GlyNAC supplementation may support healthy aging.7 An independent 2022 Nestlé trial in 114 healthy older adults confirmed safety and tolerability at multiple dose levels.
While the primary endpoint was not met in the overall population, the post-hoc finding that high-oxidative-stress, low-glutathione individuals responded significantly to medium and high doses provides important dose-targeting information.8
In a mouse study, GlyNAC supplementation was associated with a 24% increase in lifespan,9 and a 2023 mouse study showed improvements in brain glutathione, oxidative stress markers, glucose uptake, cognitive function, and neurotrophic factors in mice.10
Beyond Sleep and Glutathione — The Full Glycine Portfolio
Beyond sleep and glutathione, glycine plays roles in creatine synthesis, heme production, bile salt conjugation, and direct anti-inflammatory signaling. Beyond these effects, glycine influences several other physiological processes, including:
• Exercise physiology and performance — A 2024 review explored glycine’s potential as an ergogenic aid, noting evidence that it may enhance peak power output, reduce lactic acid accumulation during exercise, and support muscle recovery.11 However, the authors caution that high doses above 500 mg/kg of body mass could induce cytotoxic effects.
The ergogenic dimension is particularly interesting because it suggests glycine’s benefits extend to physically active populations, not just the elderly.
• Nervous system regulation and signaling — Glycine functions as an inhibitory neurotransmitter in the spinal cord and brainstem, where it modulates motor neuron excitability and reflex responses. Its role as a co-agonist at NMDA receptors throughout the central nervous system means it participates in learning, memory formation, and synaptic plasticity.
• Detoxification capacity in the liver — A 2025 Metabolism review highlighted that glycine deficiency impairs conjugation reactions in the liver — the process by which xenobiotics, drug metabolites, and endogenous toxins are attached to glycine for urinary excretion.12
When glycine is depleted, detoxification slows. In an era of increasing environmental toxin exposure, this has implications far beyond collagen metabolism.
Safety, Cost, and Practicality
The safety profile is notable. Glycine has been used in schizophrenia research at doses of 30 to 60 grams per day. A chronic high-dose study in rats found no neurotoxic effects at any dose or time point up to 5 months.13 At the 3- to 10-gram doses relevant for health, glycine appears to have a favorable safety profile at typical supplemental doses.
Glycine powder is widely available as a dietary supplement at relatively low cost. It is a white crystalline powder with a sweet taste — sweet enough to dissolve in water as a bedtime drink.
The Bottom Line
For a molecule that supports sleep, antioxidant defense, mitochondrial function, collagen synthesis, detoxification, exercise performance, and aging-related processes — glycine appears to be an underappreciated nutrient worthy of further research.
Frequently Asked Questions (FAQs) About Glycine
Q: Why is glycine considered so important for overall health?
A: Glycine supports multiple systems at once, including sleep regulation, antioxidant production, detoxification, and structural processes like collagen and creatine synthesis. Because it participates in so many pathways, changes in glycine availability can affect several aspects of your health at the same time.
Q: Why has glycine been overlooked for so long?
A: Glycine was classified as a “non-essential” amino acid because your body can produce it from serine. That classification led to the assumption that dietary intake was unnecessary, even though research shows your internal production may not meet your full physiological demand.
Q: How does glycine actually reach and affect the brain’s sleep center?
A: Research suggests glycine can cross the blood-brain barrier and act directly on receptors in the suprachiasmatic nucleus, the brain’s circadian control center, where it helps trigger the physiological changes that initiate sleep.
Q: How does glycine affect physical performance?
A: Research shows that glycine may enhance peak power output, reduce lactic acid buildup during exercise, and support muscle recovery. This suggests it has benefits for physically active individuals, not just for sleep or aging-related concerns.
Q: Do I need to take glycine consistently to see benefits?
A: The research suggests that when glycine intake is stopped, many of the improvements begin to decline. This reflects the underlying issue: Research suggests your body’s glycine demand may be ongoing. Because internal production may not fully meet that demand, maintaining adequate levels may require consistent intake rather than short-term use.
These findings are from research conducted in clinical settings. Results may not apply to all individuals.
This article is for informational purposes only and does not constitute medical advice. Consult a qualified healthcare provider before making changes to your health regimen.
Test Your Knowledge with Today’s Quiz!
Take today’s quiz to see how much you’ve learned from yesterday’s Mercola.com article.
Instead of using glucagon-like peptide-1 (GLP-1) receptor agonist drugs, what may be a more natural way to support GLP-1 levels?
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