If you’ve ever taken a sleep supplement, you’ve likely tried melatonin, magnesium, valerian, or L-theanine. But there is an amino acid that costs less per dose, is sweet enough to be used as a sugar substitute, and has a sleep mechanism that operates through a unique pathway, but few people know about it.
That amino acid is glycine. This amino acid, the smallest and simplest amino acid in nature, was discovered in 1820 and quickly classified as “non-essential” because the body can synthesize it from serine. This classification has persisted for nearly 200 years, and recent research suggests that the classification may be incomplete.
Suprachiasmatic nucleus mechanism
The story of sleep begins with Ajinomoto’s research team and the Sleep and Circadian Neurobiology Laboratory at Stanford University. In a 2015 paper published in Neuropsychopharmacology, Kawai and colleagues used a rat model to investigate the mechanisms by which glycine may promote sleep.1
• The pathways are specific and well characterized. Oral glycine can cross the blood-brain barrier and reach the suprachiasmatic nucleus (SCN), the brain’s main circadian clock. There, it binds to the glycine co-agonist site on the N-methyl-D-aspartate (NMDA) receptor in the SCN shell.
• This process initiates heat loss to support the onset of sleep. This activates neurons that trigger peripheral vasodilation, a condition in which blood vessels in the hands and feet dilate, releasing heat from the core. When core body temperature drops, non-rapid eye movement (NREM) sleep begins.
• Researchers tested this in a series of experiments. When they completely removed the SCN, glycine’s sleep effects were completely eliminated. Blocking NMDA receptors with an antagonist abolished vasodilation. However, blocking glycine receptors with strychnine had no effect. These findings suggest that this mechanism operates primarily through NMDA receptors in the SCN.
Human sleep experimental evidence
In human trials, taking 3 grams of glycine before bed improved subjective sleep quality and reduced next-day fatigue in sleep-restricted volunteers.2 A previous review from the same group explored glycine as a potential approach to support sleep quality, finding that it lowers core body temperature and improves both subjective and objective sleep quality.3
• Higher doses delivered via collagen peptides improve sleep continuity. A 2024 randomized crossover study of 13 physically active men with sleep disorders found that consuming 15 grams of glycine-rich collagen peptides before bedtime reduced sleep arousal and improved cognitive function the next morning. A study conducted in collaboration with a collagen peptide manufacturer found no effects on sleep volume, latency, or efficiency.4
• Objective sleep measures showed fewer nightly awakenings. This study used polysomnography to record fewer awakenings compared to placebo. This is notable because it suggests that the sleep effects may be dose-dependent and extended and sustained even when glycine is delivered as part of a collagen peptide matrix rather than as free glycine alone.
• Glycine’s mechanism of action is different from other sleep aids. Rather than directly regulating circadian signaling like melatonin or acting on GABA receptors like the GABAergic sedatives, glycine appears to act through thermoregulation, mimicking the natural drop in core body temperature that the body uses to initiate sleep. It also promotes physiological sleep architecture without altering brain wave patterns or causing rebound effects.
A 2015 Kawai paper suggested that glycine’s effects may be primarily mediated through the SCN, the body’s own circadian pacemaker. That means it works with the clock, rather than ignoring it.
glutathione linkage
Glycine’s benefits go beyond sleep. It is the rate-limiting substrate of glutathione synthesis. Glutathione, a tripeptide made of glycine, cysteine, and glutamic acid, is the most abundant intracellular antioxidant in the body. Insufficient glycine levels may result in decreased glutathione production.
This is what Dr. Rajagopal Sekhar’s group at Baylor College of Medicine investigated in a series of studies on glycine conjugated with N-acetylcysteine (GlyNAC), which provides the two rate-limiting precursors for glutathione synthesis.
Baylor GlyNAC Experiment — Addressing Signs of Aging
In a 2023 randomized placebo-controlled clinical trial in 24 older adults, 16 weeks of GlyNAC supplementation was associated with improvements in glutathione levels, markers of oxidative stress, mitochondrial function, inflammation, insulin resistance, endothelial function, gait speed, muscle strength, and several molecular hallmarks of aging.5
• This study examined multiple endpoints simultaneously. This was not a single endpoint study. It simultaneously addressed oxidative stress, mitochondrial dysfunction, inflammation, insulin resistance, endothelial dysfunction, genomic damage, physical function, and body composition.
• A previous 36-week open-label pilot study reported additional results. The study involved eight older and eight younger adults as the primary comparison group.
After taking the supplement for 24 weeks, older adults reported improvements in glutathione levels, mitochondrial fuel oxidation, inflammation, endothelial function, insulin resistance, cognition, muscle strength, exercise capacity, body fat, and waist circumference.6 However, as a small preliminary study, these findings require confirmation in larger controlled trials.
• In a 12-week pilot study, the benefit decreased when the supplement was discontinued. This suggested that sustained intake may be necessary to maintain adequate glycine. This is consistent with the Meléndez-Hevia model, which suggests that deficits are permanent and biochemical, rather than a one-time problem that can be resolved and forgotten.
Independent validation and dose response
A 2021 comprehensive review by Sekhar presented evidence that 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.
Although the primary endpoint was not met in the overall population, the post hoc finding that individuals with high oxidative stress and low glutathione responded significantly to the medium and high doses provides important dose target setting information.8
In a rat study, GlyNAC supplementation was associated with a 24% increase in lifespan.9 A 2023 mouse study showed improvements in brain glutathione, markers of oxidative stress, glucose uptake, cognitive function, and neurotrophic factors in mice.10
Beyond Sleep and Glutathione — Complete Glycine Portfolio
In addition to sleep and glutathione, glycine plays a role in creatine synthesis, heme production, bile salt binding, and direct anti-inflammatory signaling. In addition to these effects, glycine affects several other physiological processes, including:
• Exercise Physiology and Performance — A 2024 review explored the potential of glycine as an exercise supplement, noting evidence that it can improve maximal power output, reduce lactic acid build-up during exercise, and support muscle recovery.11 However, the authors warn that high doses above 500 mg/kg may cause cytotoxic effects.
The ergogenic dimension is particularly interesting because it suggests that the benefits of glycine extend to physically active populations as well as older adults.
• Nervous system regulation and signaling — Glycine acts as an inhibitory neurotransmitter in the spinal cord and brainstem, regulating excitability and reflex responses in motor neurons. Its role as a co-agonist at NMDA receptors throughout the central nervous system means it participates in learning, memory formation, and synaptic plasticity.
• Liver’s ability to detoxify — The 2025 Metabolism Review highlighted that glycine deficiency impairs hepatic binding reactions, the process by which xenobiotics, drug metabolites and endogenous toxins attach to glycine for urinary excretion.12
Depletion of glycine slows detoxification. In an age of increasing exposure to environmental toxins, this means more than just collagen metabolism.
Safety, cost and practicality
The safety profile is noteworthy. Glycine has been used in schizophrenia studies at doses of 30 to 60 grams per day. Chronic high-dose studies in rats showed no neurotoxic effects at any dose or time point for up to 5 months.13 Health Relevance: Glycine in doses of 3 to 10 grams appears to have a favorable safety profile at typical supplemental doses.
Glycine powder is widely available as a dietary supplement due to its relatively low cost. It is a white crystalline powder with a sweet taste. It’s sweet enough to dissolve in water for a bedtime drink.
conclusion
For molecules that support sleep, antioxidant defenses, mitochondrial function, collagen synthesis, detoxification, exercise performance, and aging-related processes, glycine appears to be an underrated nutrient worthy of further research.
Frequently Asked Questions About Glycine
cue: Why is glycine considered so important to overall health?
no way: Glycine supports multiple systems simultaneously, including sleep regulation, antioxidant production, detoxification, and structural processes such as collagen and creatine synthesis. Because glycine participates in so many pathways, changes in glycine availability can affect multiple aspects of health simultaneously.
cue: Why has glycine been overlooked for so long?
no way: Glycine has been classified as a “non-essential” amino acid because the body can produce it from serine. This classification has led to the assumption that dietary intake is unnecessary, even though studies have shown that internal production may not fully meet physiological needs.
cue: How does glycine actually reach and affect the brain’s sleep center?
no way: Studies have shown that glycine crosses the blood-brain barrier and acts directly on receptors in the suprachiasmatic nucleus, the brain’s circadian control center, which helps trigger the physiological changes that initiate sleep.
cue: How does glycine affect physical performance?
no way: Research shows that glycine can improve maximal power output, reduce lactic acid build-up during exercise, and support muscle recovery. This suggests that there may be benefits for physically active individuals as well as those with sleep or age-related issues.
cue: Do I need to take glycine consistently to see benefits?
no way: Studies show that many of the improvements begin to diminish when you stop consuming glycine. This reflects a fundamental problem. Studies have shown that the body’s need for glycine may continue. Internal production may not fully meet that demand, so consistent intake rather than short-term use may be necessary to maintain adequate levels.
These findings come from studies 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 health care provider before making any changes to your health regimen.
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