Glycine

Glycine is the simplest amino acid — its “side chain” is just a single hydrogen atom. It’s classed as non-essential because the body makes it, mainly from serine. But glycine is needed in large amounts, above all for collagen: one in every three amino acids in collagen is glycine, making it the most abundant amino acid in the body’s most abundant protein. An influential 2009 analysis estimated that the body’s own production (around 3g a day) plus typical dietary intake may fall short of total needs, and proposed that glycine should be considered conditionally essential. That’s an interesting hypothesis rather than an established fact — but it has fueled interest in glycine and collagen-rich foods, which modern diets tend to include less of. Glycine also has a surprising second life as a calming neurotransmitter, and small studies suggest it may improve sleep quality.

Classification

• Type: Non-essential amino acid — made by the body, mainly from serine; some researchers argue it may be conditionally essential when needs are high
• Structure: The simplest amino acid, with only a hydrogen atom as its side chain. It’s the only standard amino acid without left- and right-handed forms, so — unlike the others — it has no “L-” form, and its tiny size lets it fit into tight spaces in protein structures where no other amino acid could
• Metabolism: Glucogenic — glycine can be converted into serine and then pyruvate, or broken down by the glycine cleavage system, which supplies single-carbon units to the folate cycle

What Glycine Does

Collagen — the main event:

Collagen chains follow a repeating pattern in which glycine occupies every third position, with proline and hydroxyproline filling many of the other positions. When three chains wind together into the triple helix, glycine sits at the very center, where there’s room only for the smallest amino acid. The importance of this is shown by osteogenesis imperfecta (brittle bone disease): in its most severe forms, a single glycine in type I collagen is replaced by a different amino acid, disrupting the helix and making bones fragile.

Tendons, ligaments, cartilage, bone, and skin all depend on collagen. Traditional diets that used the whole animal — bone broth, skin, slow-cooked joints, and offal — provided more glycine than diets built on lean, boneless, skinless cuts. Whether this leaves most people meaningfully short of glycine hasn’t been established.

Calming neurotransmitter and sleep:

Glycine is the main inhibitory neurotransmitter in the spinal cord and brainstem, acting on glycine receptors to calm nerve activity — the poison strychnine causes violent muscle spasms by blocking these receptors. Glycine also helps activate NMDA receptors in the brain, alongside D-serine (see our serine page).

Several small trials, mostly from Japan, found that 3g of glycine taken before bed:

• Improved subjective sleep quality
• Shortened the time taken to fall asleep and reach deep sleep, in one sleep-lab study
• Reduced daytime sleepiness and fatigue, including after short-term sleep restriction

In animal studies, glycine acted on the brain’s body clock to widen blood vessels in the skin, lowering core body temperature — one of the body’s natural signals for sleep. The evidence is promising but limited: the trials were small and short, and several were carried out or funded by a glycine manufacturer. With that caveat, glycine is cheap, well tolerated, and a reasonable thing to try for mild sleep problems.

Creatine production:

The body makes creatine from glycine, arginine, and methionine, with glycine forming the creatine backbone. Creatine supplements reduce the body’s own creatine production, which in theory frees up some glycine for other uses.

Glutathione:

Glycine is one of the three building blocks of glutathione, the main antioxidant inside cells, along with cysteine and glutamate. Cysteine is usually the limiting building block, but in older adults, glycine may also run short: small trials of glycine combined with N-acetylcysteine (known as GlyNAC) raised glutathione levels and improved several markers of oxidative stress in older people. Larger trials are needed.

Digestion:

The liver attaches glycine (or taurine) to bile acids, forming bile salts such as glycocholic acid, which help digest and absorb dietary fat and fat-soluble vitamins.

Recommended Intake

There’s no RDA for glycine. A typical diet provides roughly 3–5g a day, and the body makes more. The 2009 analysis mentioned above estimated total needs at around 10g a day, but that figure is theoretical.

Practical uses studied in research:

• Sleep: 3g before bed
• Connective tissue: about 15g of gelatin or collagen (which is roughly a fifth glycine) with vitamin C before training — see below

Found In (per 100g)

Gelatin and collagen are by far the richest sources: USDA data show about 19g of glycine per 100g of unflavored gelatin powder, and about 12g per 100g of plain pork skins (pork rinds). Per gram of protein, gelatin provides about four to five times as much glycine as muscle meat. Sesame seeds provide about 1.2g per 100g.

Among everyday foods, ground beef — which includes more connective tissue — has a higher share of glycine than lean chicken breast, and nuts and seeds are also good sources. Dairy is notably low: casein, the main milk protein, is rich in proline but poor in glycine. Bone broth provides glycine from simmered bones and connective tissue, but analyses show the amounts are low and highly variable.

Helps With

• Collagen production for tendons, ligaments, cartilage, skin, and bone
• Possibly sleep quality — 3g before bed in small studies
• Calming nerve signalling in the spinal cord and brainstem
• Creatine production
• Glutathione production for antioxidant defense
• Bile salt production for fat digestion
• Wound healing and tissue repair, through collagen

Glycine for Athletes and Active People

Connective tissue under load: heavy lifting, running, and jumping place repeated stress on tendons and ligaments, which have a limited blood supply and adapt over months and years rather than days. Adequate protein, energy, and vitamin C are the nutritional foundation, and well-planned increases in training load matter most — injury risk is highest when volume rises quickly.

The gelatin and vitamin C protocol: taking about 15g of gelatin with roughly 50mg of vitamin C about an hour before a short bout of loading exercise doubled a blood marker of collagen production in a 2017 study. Gelatin is about a fifth glycine, so there’s no need to add extra glycine powder. Long-term evidence for tendon strength and injury prevention is still limited. See our vitamin C and proline pages for details.

Sleep and recovery: for athletes whose sleep is suffering during hard training blocks, 3g of glycine before bed is a cheap, low-risk option with some supporting evidence. It’s no substitute for the basics — a consistent schedule, enough time in bed, and a dark, cool room.

Oxidative stress: hard training increases oxidative stress, and glutathione is part of the defense. In younger athletes eating enough protein, cysteine rather than glycine is usually the limiting building block, and there’s no evidence that glycine supplements improve recovery. High-dose antioxidant supplements may even blunt some training adaptations.

Older athletes: collagen turnover and glutathione levels both decline with age, and older athletes are more prone to tendon problems. That makes collagen-rich foods or supplements and the gelatin protocol more appealing for masters athletes, although the evidence is still emerging.

Glycine Deficiency

There’s no recognized dietary glycine deficiency. Lower blood glycine levels have been linked with obesity, type 2 diabetes, and fatty liver disease, but it isn’t clear whether low glycine contributes to these conditions or simply reflects them. Common problems such as slow injury recovery, tendon pain, or poor sleep have many causes and aren’t reliable signs of low glycine.

Inherited glycine disorders: in glycine encephalopathy (nonketotic hyperglycinemia), the glycine cleavage system doesn’t work, so glycine builds up in the brain, causing severe seizures and developmental problems from birth. It’s managed with sodium benzoate, which helps remove glycine, and medicines that dampen NMDA receptor overactivity. In hyperekplexia (“startle disease”), faulty glycine receptors cause exaggerated startle reactions and stiffness.

Excessive Glycine

No formal upper limit has been set. At typical supplement doses of 3–5g a day, glycine is very well tolerated. Much higher doses — around 60g a day, used in trials in schizophrenia — have been tolerated in research settings, but with side effects such as nausea and vomiting in some people.

Clozapine: in a trial in people with schizophrenia, adding high-dose glycine to the antipsychotic clozapine didn’t help, and may have worsened symptoms. Anyone taking clozapine should check with their doctor before taking glycine supplements.

Types and Forms

• Glycine powder: inexpensive, mildly sweet, and dissolves easily in water or protein shakes. It’s sometimes labelled “L-glycine,” but since glycine has no left- or right-handed forms, it’s simply glycine.
• Collagen peptides: collagen broken into small peptides that dissolve easily; about a fifth glycine, along with proline and hydroxyproline.
• Gelatin: collagen that has been partly broken down by cooking; the same amino acid profile as collagen peptides, but it gels and needs warm liquid to dissolve. It was the form used in the gelatin and vitamin C study.
• Bone broth: a food source of glycine, but the amounts are low and vary widely.
• Mineral glycinates: magnesium glycinate, zinc glycinate, and similar supplements use glycine as the partner molecule for the mineral. They provide only small amounts of glycine.

Which form for your goal:

How to Take Glycine

For sleep: 3g dissolved in water, about an hour before bed. Its mild sweetness makes it easy to take.

For connective tissue: use gelatin or collagen rather than glycine powder — about 15g with roughly 50mg of vitamin C, an hour before training that loads the target tissue, alongside a structured loading program.

Bone broth: broth made from collagen-rich parts (chicken feet, knuckle bones, oxtail, or pig trotters) and simmered for many hours will gel when cooled — a sign that gelatin has been extracted. It’s a nice food, but don’t rely on it for consistent doses.

If you take clozapine: talk to your doctor before taking glycine supplements.

Interactions

Vitamin C is needed to convert proline into hydroxyproline in new collagen, without which collagen is unstable. Proline is collagen’s other main amino acid, and collagen products provide both together. Serine and glycine are converted back and forth by the enzyme SHMT, which needs vitamin B6 — serine is the body’s main source of glycine. High-dose glycine may interact with clozapine.

Synergy

• Works with proline and hydroxyproline in collagen — together, the three make up more than half of collagen’s amino acids.
• Works with vitamin C, which stabilizes collagen by forming hydroxyproline.
• Works with cysteine and glutamate to make glutathione.
• Works with arginine and methionine to make creatine.
• Works with serine, its main precursor, and with the folate cycle, through the glycine cleavage system.

Antagonistic Interactions

• Strychnine blocks glycine receptors, removing glycine’s calming effect on nerves — a poisoning mechanism, not a dietary concern.
• High-dose glycine may worsen symptoms in people taking clozapine.

Food values: USDA FoodData Central, SR Legacy — pumpkin and squash seed kernels, dried (FDC ID 170556)*; ground beef, 80% lean, cooked (171797); peanuts, raw (172430)*; chicken breast, roasted (171477); almonds (170567)*; turkey breast, roasted (174516); yellowfin tuna, cooked (172006); pork top loin chop, broiled (167841); sardines, canned in oil (175139); Atlantic salmon, farmed, cooked (175168); tofu, firm, calcium-set (172475); oats, dry (173904); parmesan, hard (170848); egg, hard-boiled (173424); chickpeas, cooked (173757); lentils, cooked (172421); black beans, cooked (173735); cottage cheese, low-fat, 2% (172182)*; white rice, cooked (168878). * SR Legacy values used as fill-ins for the Foundation Foods entries for pumpkin seeds (2515380), peanuts (2515376), almonds (2346393), and cottage cheese (328841), whose amino acid data aren’t included in our tracker. Glycine as % of protein is calculated from the same USDA records; the gelatin, pork skin, and sesame figures are from USDA SR Legacy data.