Story
Glycine
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In one pass Glycine (abbreviated Gly or G) is the smallest of the 20 amino acids that make up proteins: its side chain is a single hydrogen atom.
Educational content, not medical advice — consult a clinician.
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Chapter 1
Does the body make enough?
Glycine (abbreviated Gly or G) is the smallest of the 20 amino acids that make up proteins: its side chain is a single hydrogen atom. Because it is so small, it fits where other amino acids cannot, such as the tightest center of the collagen triple helix.
Textbooks list it as non-essential, meaning the body can make it. The question is whether it makes enough. Meléndez-Hevia 2009 (J Biosci) added up the published figures for glycine production and use item by item and estimated that for a 70 kg adult, what the body makes plus what an ordinary diet supplies may fall about 10 g a day short of all its uses. This is an estimate assembled from literature data, not a shortfall measured directly in people.
On that basis, some researchers argue that glycine should count as conditionally essential: the body can make some, but under certain conditions not enough, so food has to make up the rest. Glutamine, arginine, cysteine and tyrosine belong to the same group, a third case outside the textbook split between essential and non-essential.
Textbooks list it as non-essential, meaning the body can make it. The question is whether it makes enough. Meléndez-Hevia 2009 (J Biosci) added up the published figures for glycine production and use item by item and estimated that for a 70 kg adult, what the body makes plus what an ordinary diet supplies may fall about 10 g a day short of all its uses. This is an estimate assembled from literature data, not a shortfall measured directly in people.
On that basis, some researchers argue that glycine should count as conditionally essential: the body can make some, but under certain conditions not enough, so food has to make up the rest. Glutamine, arginine, cysteine and tyrosine belong to the same group, a third case outside the textbook split between essential and non-essential.
In practice · Which foods supply glycine
Glycine in the diet (per 100 g of protein):Gelatin, collagen and bone broth: about 25–30 g, far ahead of everything else. In collagen, 1 amino acid in every 3 is glycine (about 33% by count)Egg white: about 3 gChicken breast, red meat and fish: about 3–5 g (mostly from the collagen in connective tissue and the membranes around muscle)Soy and other beans: about 4–5 gWhey protein: about 1.5–2 g, very little glycineGrains and vegetables: about 3–4 g
What this means for eating:
1. If you eat only lean meat, chicken breast and whey protein, your glycine intake can stay low even when your total protein is very high (common in fitness diets)
2. Eating the whole animal, connective tissue included (traditional cooking, whole chicken, bone broth, tripe, chicken feet, fish skin) supplies far more glycine
3. Strict vegans who get their protein from soy or pea protein powders usually have a low glycine intake too
In the kitchen: eating a whole chicken (skin, bones and broth) gives you clearly more glycine than eating only the breast. You can deliberately add collagen sources to your diet: gelatin stirred into water (5–15 g), bone broth, fish skin, chicken wings, tendon. Or take plain glycine powder, one of the cheapest amino acids among supplements, and much cheaper per gram of glycine than collagen peptides.
Note: this is not a muscle-building supplement. People take it for collagen, glutathione and sleep; the only ones tested in human trials are sleep (a few small trials) and raising glutathione in combination with (one small trial).
Numbers · How the shortfall was estimated
The body can indeed make its own glycine. It starts from serine, and an enzyme called SHMT (serine hydroxymethyltransferase) converts it, handing a one-carbon unit on to one-carbon metabolism as it does. So whether it can be made was never the dispute. The dispute is whether enough is made.Lay out both sides of the ledger (the estimate in Meléndez-Hevia 2009):
Made by the body (the SHMT pathway from serine): about 2.5–3 g a dayUsed by collagen, glutathione (GSH), creatine, heme and neurotransmitters together: about 10–15 g a dayA typical Western diet adds 1.5–3 g a day (eggs, meat or beans, gelatin), still not enough to close the gap of about 10 g a day
That is as far as the paper goes. It did not find a new use for glycine; it added up the known uses one by one and found that the supply side does not match. It is an estimate, its figures depend on how each use is estimated, and other researchers estimate the body's own synthesis differently. The conditionally essential category exists because an amino acid can be both makeable and not enough, and the split between essential and non-essential has no box for that case.
Chapter 2
Five jobs for one amino acid
Your body needs glycine for five jobs every day, and there is only one pool for all of them: whatever one job takes, the others lose.
1. Skin, tendon and cartilage use it to build collagen. Every third position in collagen has to be glycine; no other amino acid fits there.
2. Almost every cell uses it to assemble glutathione (GSH), the body's own main antioxidant.
3. The kidney and liver pass it along between them to make creatine, which muscle stores as a reserve of energy for bursts of effort.
4. Bone marrow uses it to build the ring of heme, the part of the red blood cell that holds on to oxygen.
5. The spinal cord and brainstem use it as a brake signal that quiets motor neurons; in the brain, it is also the partner that must be present before the NMDA receptor (a kind of excitatory receptor) will open.
So if glycine really does run short (itself still a hypothesis), the mechanism predicts that the effect would not fall on one pathway alone but would squeeze several at once. It is one of the few amino acids that serves structure (collagen), metabolism (glutathione, creatine, heme) and signaling (neurotransmitters) all at once.
1. Skin, tendon and cartilage use it to build collagen. Every third position in collagen has to be glycine; no other amino acid fits there.
2. Almost every cell uses it to assemble glutathione (GSH), the body's own main antioxidant.
3. The kidney and liver pass it along between them to make creatine, which muscle stores as a reserve of energy for bursts of effort.
4. Bone marrow uses it to build the ring of heme, the part of the red blood cell that holds on to oxygen.
5. The spinal cord and brainstem use it as a brake signal that quiets motor neurons; in the brain, it is also the partner that must be present before the NMDA receptor (a kind of excitatory receptor) will open.
So if glycine really does run short (itself still a hypothesis), the mechanism predicts that the effect would not fall on one pathway alone but would squeeze several at once. It is one of the few amino acids that serves structure (collagen), metabolism (glutathione, creatine, heme) and signaling (neurotransmitters) all at once.
Mechanism · Why teach it as a hub
Nutrition textbooks usually sort amino acids into essential and non-essential, then describe them one at a time. That approach misses the metabolic links between them: a few amino acids work like transport hubs, feeding several pathways at once.Glycine: feeds five pathways, plus a nerve signalCysteine (Cys): glutathione, taurine, coenzyme A, and the disulfide bonds that hold protein structures togetherGlutamate and glutamine (Glu, Gln): neurotransmitters, purine synthesis, nitrogen balance, glutathioneMethionine (Met): S-adenosylmethionine (, the body's general-purpose methyl donor), conversion to cysteine, carnitine synthesisTryptophan (Trp): serotonin (, a neurotransmitter), niacin, melatonin
By the mechanism, a long-term shortage of any of these hub amino acids would affect several systems at once. Yet when textbooks reach nutrition, they usually just list these amino acids in a table and do not lay out how one hub connects to several pathways.
Seeing amino acids as a metabolic network, rather than 20 unrelated entries, makes it easier to understand why one ordinary-looking amino acid turns up in stories about skin, blood, muscle and sleep all at once.
Mechanism · Enzymes and reactions on five paths
Collagen synthesis (the largest consumer)The triple helix is a repeat of Gly-X-Y, with glycine at every third position, so by count about 33% of collagen is glycine. By Meléndez-Hevia's estimate, adults make 10–20 g of collagen a day, using 3–7 g of glycine. The Collagen peptides story explains why collagen is so rich in glycine; seen from the other side, collagen synthesis keeps drawing on the glycine pool.
Glutathione (GSH) synthesis
GSH is γ-glutamyl-cysteinyl-glycine (γ-Glu-Cys-Gly), with glycine as the third amino acid. Glutathione synthetase (GSS) joins γ-Glu-Cys and glycine into GSH. In the story, the rate-limiting raw material is cysteine; by the mechanism, if glycine runs short for a long time, it could become a secondary bottleneck.
Creatine synthesis
Creatine is made in two steps:
AGAT (in the kidney): glycine + arginine → guanidinoacetate (GAA) + ornithineGAMT (in the liver): GAA + → creatine + S-adenosylhomocysteine (SAH)
Glycine provides creatine's carbon backbone. Vegetarians have lower creatine levels mainly because they get none of the creatine found in meat; taking creatine bypasses the body's own synthesis.
Heme synthesis
The first step in building the porphyrin ring (also covered in the heme-making chapter of the iron story) is the mitochondrial enzyme ALAS joining glycine and succinyl-CoA into δ-aminolevulinic acid () and CO₂. Each porphyrin ring uses 8 glycines. The body makes about 2 million new red blood cells every second, steadily drawing glycine into the heme production line.
An inhibitory neurotransmitter, and the NMDA receptor's partner
In the spinal cord and brainstem, glycine is a classic inhibitory neurotransmitter (acting much like , a signal that quiets neurons). It binds the glycine receptor (GlyR), a chloride channel, and inhibits motor neurons. Tetanus toxin causes muscle rigidity precisely by blocking glycine release. In the brain, glycine is also an obligatory co-agonist of the NMDA receptor (it must be present together with glutamate before the channel opens), which takes part in learning, memory and neural plasticity. In rat experiments, the route by which glycine taken at bedtime helps sleep is the second one, NMDA receptors in the suprachiasmatic nucleus, not the inhibitory glycine receptor (the chapter on taking it before bed has the details).
Glycine is one of the few amino acids that takes part in structure (collagen), metabolism (glutathione, creatine, heme) and signaling (neurotransmitters). By the mechanism, a shortage would not stay confined to one pathway.
Chapter 3
How it helps sleep
Glycine's most promoted use is to help sleep. The human evidence comes from a few small crossover trials by the same group in Japan (each person took glycine and a placebo in turn, acting as their own control), and the authors include researchers from Ajinomoto, a company that makes amino acids.
The key one is Yamadera 2007. Eleven people who had long felt they slept badly took 3 g of glycine before bed. Compared with placebo, they rated their sleep quality better. (an all-night recording of brain waves, eye movements and muscle activity) showed that they fell asleep faster and reached deep sleep sooner, with no change in the structure of their sleep, and they felt less sleepy the next morning. An earlier trial in 19 women who slept badly found less fatigue the next morning.
It works differently from the usual sleep aids: it is not a sedative and not melatonin. Rat experiments suggest that it acts on the suprachiasmatic nucleus (, the body's rhythm center) in the hypothalamus, widening skin blood vessels and lowering core body temperature, and falling asleep normally comes with a drop in body temperature. That step has not yet been shown directly in people.
The key one is Yamadera 2007. Eleven people who had long felt they slept badly took 3 g of glycine before bed. Compared with placebo, they rated their sleep quality better. (an all-night recording of brain waves, eye movements and muscle activity) showed that they fell asleep faster and reached deep sleep sooner, with no change in the structure of their sleep, and they felt less sleepy the next morning. An earlier trial in 19 women who slept badly found less fatigue the next morning.
It works differently from the usual sleep aids: it is not a sedative and not melatonin. Rat experiments suggest that it acts on the suprachiasmatic nucleus (, the body's rhythm center) in the hypothalamus, widening skin blood vessels and lowering core body temperature, and falling asleep normally comes with a drop in body temperature. That step has not yet been shown directly in people.
In practice · How to use it, what not to expect
How to take it (following the trials):3 g of glycine powder, 30–60 minutes before bedStir it straight into water (glycine dissolves easily, tastes slightly sweet and needs no flavoring)Or eat more glycine-rich foods and have a cup of bone broth (5–15 g of gelatin contains about 1.5–5 g of glycine)Use it for 2–4 weeks and see whether you notice a difference; the trials themselves measured only one night or a few
What not to expect:
It does not knock you out. It improves sleep quality; it is not a strong sedativeIt will not make you sleep 12 hours: people fell asleep faster, but no longer total sleep time was reportedInsomnia driven by anxiety or depression, and long-term chronic insomnia, need professional treatment. The first-line treatment for chronic insomnia is cognitive behavioral therapy for insomnia (); see the Insomnia storyIt does not replace the basics: dim light before bed, no alcohol, a cool bedroom and regular sleep times
Cautions:
Chronic kidney disease: be careful with high protein and large amino-acid loads, and ask your doctor firstTaking clozapine or other antipsychotics: glycine acts on NMDA receptors and may interact with the drug, so ask your doctor firstPregnancy and breastfeeding: there are no dedicated data. Glycine from food is fine; avoid large supplement doses
Evidence · What the glycine sleep trials measured
The full results of Yamadera 2007 (Sleep and Biological Rhythms; randomized, single-blind, crossover, 11 people with long-standing poor sleep):Self-rated: more satisfied with their sleep, less difficulty falling asleep, and better sleep efficiency (the share of time in bed actually spent asleep), measured with the St. Mary's Hospital Sleep Questionnaire: sleep-onset latency (the time from lights out to falling asleep) was shorter, and slow-wave (deep) sleep arrived sooner; sleep architecture (the proportions of the sleep stages) did not changeThe next day: less sleepiness in the morning, and better performance on a memory-recognition test
Earlier and related trials by the same group (as summarized in the Bannai 2012 review): Inagawa 2006 was a randomized, double-blind crossover trial in which 19 women with poor sleep took 3 g and felt less fatigued the next morning. An open trial gave 9 g during the day to 12 people with normal sleep; it caused no sleepiness and no adverse effects. In an earlier study, 31 g a day produced no serious side effects either.
Details of the cooling route (Bannai 2012, rat experiments): 30 minutes after a large oral dose of 2 g per kilogram of body weight, plasma glycine rose to 13 times the control level and cerebrospinal-fluid glycine to 6 times. Glycine acts on NMDA receptors in the suprachiasmatic nucleus, widening skin blood vessels and lowering core body temperature. Blocking NMDA receptors stopped this effect; blocking the inhibitory glycine receptor did not. So the inhibitory route that quiets motor neurons is not the main explanation for how oral glycine helps sleep. How much blood glycine rises after 3 g in a person, and whether the same route works in people, has not been measured directly.
How to read these results:
The samples are all small (11 people, 19 people), all from the same research group, and the authors include researchers from a company that makes amino acids. Larger, independent trials are needed to repeat them.The trials looked at one night or a few, so tolerance, dependence and rebound after stopping have not been measured.Not feeling sleepy the next day was seen both in Yamadera 2007 and in the 9 g safety trial.
Set alongside other sleep aids (the types of evidence differ, so do not compare size alone):
Melatonin: its best-supported use is jet lag, usually at small doses such as 0.3–0.5 mg (see the Melatonin story); for general insomnia the effect is smallGlycine 3 g: a few small crossover trials, showing effects on self-rated sleep quality and sleep-onset latencyTheanine 200 mg: some small trials on feeling relaxed; weak objective sleep dataMagnesium 200–400 mg: more likely to help people who are short of magnesium; a weak signal in everyone elseCognitive behavioral therapy for insomnia (): the first-line treatment for chronic insomnia
Glycine is cheap and has a good safety record, but the line its sleep evidence is firmer than most sleep supplements' says too much. Its evidence is a few small trials, not large studies.
Chapter 4
Collagen and glutathione compete
Connect the two most glycine-hungry exits back to the source, and you can see how they drag on each other.
Loop 1, collagen: your tendons, skin and cartilage are taking down old collagen and building new every day. Building uses glycine, and what is taken down returns glycine to the pool. Training, aging and injury all speed up this round trip, so the pool is drawn down harder over the same period. The core hypothesis of Meléndez-Hevia 2009 is that athletes' chronic joint pain, older people's thinning skin and wounds that are slow to heal may partly reflect a pool that cannot keep up with repair. It is a hypothesis and has not been tested directly in people.
Loop 2, glutathione (GSH): the cell's main antioxidant, whose last building block is glycine. Usually the bottleneck is cysteine. By the mechanism, once cysteine is sufficient but glycine has been short for a long time, the slow step would switch to glycine.
The whole picture looks like this: what you eat, plus the little the body makes itself (about 3 g a day), forms one glycine pool, and five exits (collagen, glutathione, creatine, heme and neurotransmitters) compete for it at the same time. That is why Meléndez-Hevia calls it a weak link in metabolism: not because it is especially important, but because by their estimate demand exceeds supply and there is no backup.
Loop 1, collagen: your tendons, skin and cartilage are taking down old collagen and building new every day. Building uses glycine, and what is taken down returns glycine to the pool. Training, aging and injury all speed up this round trip, so the pool is drawn down harder over the same period. The core hypothesis of Meléndez-Hevia 2009 is that athletes' chronic joint pain, older people's thinning skin and wounds that are slow to heal may partly reflect a pool that cannot keep up with repair. It is a hypothesis and has not been tested directly in people.
Loop 2, glutathione (GSH): the cell's main antioxidant, whose last building block is glycine. Usually the bottleneck is cysteine. By the mechanism, once cysteine is sufficient but glycine has been short for a long time, the slow step would switch to glycine.
The whole picture looks like this: what you eat, plus the little the body makes itself (about 3 g a day), forms one glycine pool, and five exits (collagen, glutathione, creatine, heme and neurotransmitters) compete for it at the same time. That is why Meléndez-Hevia calls it a weak link in metabolism: not because it is especially important, but because by their estimate demand exceeds supply and there is no backup.
Mechanism · The creatine and heme exits
One molecule, five exits: the creatine and heme routes also need to be spelled out.The creatine loop
Creatine is made in two steps. AGAT, in the kidney, joins glycine and arginine into GAA (guanidinoacetate); GAMT, in the liver, joins GAA and into creatine. The second step uses a large number of methyl groups, about 40–70% of the body's SAM use. The body makes about 1.5–2 g of creatine a day, using about 0.5 g of glycine, about 1 g of arginine and a large amount of methyl.
Vegans and vegetarians have lower creatine levels mainly because they eat no meat (meat is the main food source of creatine) and rely entirely on their own synthesis. Taking creatine (3–5 g a day) bypasses that synthesis, and by the mechanism it would also free some glycine for other pathways. Some researchers suspect that people who eat no meat may gain more from creatine, but this is not settled.
The heme loop
In the mitochondria, ALAS joins glycine and succinyl-CoA into . Eight ALA molecules assemble one porphyrin ring, and adding one Fe²⁺ gives heme. Red blood cells live about 120 days, and about 1% are replaced each day, steadily drawing glycine into this production line. By the mechanism, blood loss, menstruation and pregnancy speed up blood-making and so raise the demand for glycine. Whether a low glycine intake can make blood-making fall behind (even when iron is sufficient) has not been measured directly in people.
The neurotransmitter loop
Inhibitory: glycine receptors (chloride channels) in the spinal cord and brainstem. Tetanus toxin blocks glycine release; with the inhibition gone, nerves keep firing and muscles lock rigidExcitatory partner: an obligatory co-agonist of the NMDA receptor (glycine and glutamate must both be present), taking part in learning, memory and long-term potentiation (LTP, the lasting strengthening of a synaptic connection)Sleep: in rat experiments, oral glycine lowers core body temperature through NMDA receptors in the suprachiasmatic nucleus, which helps sleep onset
Glycine connects to protein, iron, , creatine, collagen and the nervous system, which is why it is worth treating on its own: filed under miscellaneous amino acids, these connections disappear from view.
In practice · Reactions and amounts on both loops
Loop 1: glycine and collagenCollagen synthesis uses glycine (3–7 g a day, by Meléndez-Hevia's estimate)Collagen breakdown returns glycine, proline (Pro) and hydroxyproline (Hyp) to the amino-acid poolTraining, aging and injury speed up collagen turnover and raise the demand on glycine
In practice: if you already follow the Shaw 2017 routine described in the Collagen peptides story, taking 5–15 g of gelatin plus 50 mg of vitamin C before training, you are also getting a good amount of glycine (5–15 g of gelatin contains about 1.5–5 g). Whether plain glycine powder plus vitamin C can stand in for gelatin has not been compared in a trial. Collagen peptides also carry a hypothesis that the Gly-Pro-Hyp tripeptide acts as a signal, so the two cannot simply be treated as equal.
Loop 2: glycine and glutathione
GSH is γ-Glu-Cys-Gly; the third amino acid is glycineThe enzyme GSS joins γ-Glu-Cys and glycine into GSHWhen cysteine is sufficient and glycine is short, the mechanism predicts that glycine will hold back the rate of GSH synthesis (although the main rate-limiting raw material is cysteine)A review by Pérez-Torres 2017 proposes that in older people and in those with diabetes or chronic inflammation, lower GSH synthesis may partly reflect a shortage of glycine
In practice: if you already take (to raise cysteine), adding glycine might, by the mechanism, raise the ceiling on GSH synthesis a little further. It is a secondary bottleneck, and in most cases NAC alone is enough. The glycine-plus-NAC combination (GlyNAC) has one small randomized trial: Kumar 2023 (J Gerontol A) gave it to older adults, 12 per group, for 16 weeks, and markers such as glutathione deficiency and oxidative stress improved. It is an emerging line of research with a very small sample, and it needs larger trials.
Put the two loops side by side and you see they draw on the same account. Someone who is training hard (fast collagen turnover) while living with chronic inflammation (heavy GSH use) has both paths reaching into the pool at once, and the pool does not grow because of it.
Chapter 5
Who should take it, and how
Glycine is a shared building block of collagen, glutathione, creatine and heme. People whose total protein is adequate but who eat only lean meat and whey often get too little of it. Vegetarians may get less glycine from food, and they rely entirely on their own synthesis for creatine. Taken before bed for sleep, it works, according to rat experiments, through temperature regulation, and the human evidence is only a few small trials.
It is cheap and has a good safety record, with no marketing buzz, which is also why few people notice it. Do not use magnesium glycinate as a way to get glycine: it is a magnesium product with little glycine in it.
It is cheap and has a good safety record, with no marketing buzz, which is also why few people notice it. Do not use magnesium glycinate as a way to get glycine: it is a magnesium product with little glycine in it.
In practice · Who might consider it
Do you need to supplement glycine? The six situations below are the ones most worth considering, but the evidence behind each differs in strength.People for whom it may make sense:
1. People who eat only lean meat, chicken breast and whey: enough total protein, too little glycine. You could take 3–5 g of glycine powder a day, a little more on training days. This advice comes from adding up the diet; no trial has measured its effect
2. People who sleep poorly or fall asleep slowly: 3 g before bed (Yamadera 2007, a few small crossover trials)
3. Vegans and vegetarians: low glycine intake and complete reliance on their own creatine synthesis, so taking both glycine and creatine is worth considering
4. People with joint pain from years of training, or older adults whose tissues repair slowly: 3–10 g a day, tried for 2–3 months. This comes from reasoning about the collagen loop and has not been tested directly in human trials
5. Chronic inflammation, diabetes or metabolic syndrome: glycine plus (GlyNAC) is an emerging direction, with only one small trial of 12 people per group so far
6. During menstruation or after giving birth: by the mechanism, demand may rise, so eat more glycine-rich food first. Pregnancy and breastfeeding lack dedicated data, so do not take large supplement doses on your own
Doses:
For sleep: 3 g before bedEveryday top-up: 5 g a day, at any timeTraining and repair: 5–10 g a day, 2–3 g after training and the other 2–5 g spread over mealsGlyNAC (older adults, antioxidant): the Kumar 2023 trial dosed by body weight, 100 mg/kg of glycine a day (about 7–10 g) plus NAC also dosed by body weight. It has been used only in small trials, so do not copy it on your own
Safety:
Glycine is an amino acid that is already in food. In an early study cited by Bannai 2012, 31 g a day caused no serious side effects, and a 9 g safety trial found no adverse effectsIn the 16-week GlyNAC trial, the weight-based doses were safe and well toleratedIf you have chronic kidney disease, take antipsychotics, or are pregnant or breastfeeding, ask your doctor first
In practice · Other inexpensive amino acids
The supplement shelf holds a few other cheap, overlooked amino acids that most shoppers have never heard of. Cheap is not the same as effective, so look at the evidence behind each:Glycine (Gly): a hub molecule, linked to collagen, glutathione, creatine, heme and sleep; its human evidence is mainly a few small sleep trialsTaurine: strictly an amino-acid-like molecule (it carries -SO₃H, not -COOH), involved in cardiovascular function, osmotic balance, bile-acid conjugation and antioxidant protection in the retina. A common amount is 1–3 g a day; there are some small trials, and their conclusions are not yet consistentLysine (Lys): an essential amino acid, a raw material used by the enzymes that cross-link collagen, and the one most easily short in diets built on grains and rice. It is rarely taken on its own; diet is the main sourceArginine (Arg): a semi-essential amino acid, a raw material for the nitric oxide () pathway and a precursor of creatine and ornithine. To raise nitric oxide, citrulline is usually the more practical choice (it has its own story)Methionine (Met): an essential amino acid at the center of methylation, but too much of it raises (Hcy), so do not add it on your ownTryptophan (Trp): an essential amino acid and the precursor of serotonin (), niacin and melatonin. Eating tryptophan-rich foods in the evening (turkey, milk) is the safer route; taking tryptophan on its own, especially together with antidepressants, carries a risk of serotonin syndrome
How to combine them:
Getting started: 5 g of glycine a day plus the basics (protein, fruit and vegetables, training, sleep), and see whether anything changes over 4–6 weeksOne step further: glycine 5 g, 600 mg and creatine 5 g, three hub molecules together, still at a modest monthly costFor sleep: 3 g of glycine before bedFor antioxidant support: NAC plus glycine (GlyNAC)For exercise performance: creatine plus glycine, with enough total protein
When you see an ad for a revolutionary new molecule at a steep monthly price, think of these cheap old molecules first, then decide.
In practice · Which form to buy and what it costs
Glycine gets little attention. It is cheap, has a good safety record and a clear mechanism, but it has no marketing buzz, because it is too cheap to support a brand premium. To be clear, though, its sleep evidence is a few small trials and cannot be called robust clinical evidence.Price:
Glycine powder: one of the cheapest amino acids among supplements; 5 g a day costs very littleCollagen peptides: about one third glycine (by count), and several times more expensive than glycine powder per gram of glycineWhey protein: only 1.5–2% glycine, the most expensive way to get it
Being cheap does not prove that something works; it only means that no miracle molecule story is pushing the price up.
The form to buy:
Pure glycine powder (food grade): the best valueDo not buy magnesium glycinate to get glycine: it is a magnesium supplement, and although it contains some glycine, the amount is small and the price is highDo not buy capsules: each one holds too little to be worth itDo not buy mixed amino-acid blends: the dose of each ingredient is unclear, and you pay a marketing premium
If you want to try a low-risk supplement, 3 g before bed or 5 g a day to fill a dietary gap are both reasonable starting points. If you have chronic kidney disease, take antipsychotics, or are pregnant or breastfeeding, ask your doctor first.
References · 8
- Meléndez-Hevia, E., De Paz-Lugo, P., Cornish-Bowden, A., & Cárdenas, M. L. (2009). A weak link in metabolism: the metabolic capacity for glycine biosynthesis does not satisfy the need for collagen synthesis. Journal of Biosciences, 34(6), 853-872. 10.1007/s12038-009-0100-9
- Razak, M. A., Begum, P. S., Viswanath, B., & Rajagopal, S. (2017). Multifarious beneficial effect of nonessential amino acid, glycine: a review. Oxidative Medicine and Cellular Longevity, 2017, 1716701. 10.1155/2017/1716701
- Bannai, M., & Kawai, N. (2012). New therapeutic strategy for amino acid medicine: glycine improves the quality of sleep. Journal of Pharmacological Sciences, 118(2), 145-148. 10.1254/jphs.11R04FM
- Yamadera, W., Inagawa, K., Chiba, S., Bannai, M., Takahashi, M., & Nakayama, K. (2007). Glycine ingestion improves subjective sleep quality in human volunteers, correlating with polysomnographic changes. Sleep and Biological Rhythms, 5(2), 126-131. 10.1111/j.1479-8425.2007.00262.x
- Pérez-Torres, I., Zúñiga-Muñoz, A. M., & Guarner-Lans, V. (2017). Beneficial effects of the amino acid glycine. Mini-Reviews in Medicinal Chemistry, 17(1), 15-32. 10.2174/1389557516666160609081602
- Shaw, G., Lee-Barthel, A., Ross, M. L. R., Wang, B., & Baar, K. (2017). Vitamin C-enriched gelatin supplementation before intermittent activity augments collagen synthesis. The American Journal of Clinical Nutrition, 105(1), 136-143. 8 healthy men, randomized double-blind crossover: 5 g or 15 g vitamin C-enriched gelatin or placebo 1 h before 6 min of rope-skipping, 3 times a day for 3 days. Blood glycine, proline, hydroxyproline and hydroxylysine peaked 1 h after the drink; with 15 g gelatin, blood amino-terminal propeptide of collagen I (PINP) doubled; serum drawn after gelatin raised collagen content of engineered ligaments in vitro. A collagen-synthesis marker; no injury or recovery outcome was measured (abstract, PMID 27852613). 10.3945/ajcn.116.138594
- Kumar, P., Liu, C., Suliburk, J., Hsu, J. W., Muthupillai, R., Jahoor, F., Minard, C. G., Taffet, G. E., & Sekhar, R. V. (2023). Supplementing glycine and N-acetylcysteine (GlyNAC) in older adults improves glutathione deficiency, oxidative stress, mitochondrial dysfunction, inflammation, physical function, and aging hallmarks: A randomized clinical trial. The Journals of Gerontology: Series A, 78(1), 75-89. 10.1093/gerona/glac135
- Forbes, S. C., Cordingley, D. M., Cornish, S. M., et al. (2022). Effects of creatine supplementation on brain function and health. Nutrients, 14(5), 921. 10.3390/nu14050921