Glycine is an amino acid, one of the basic building blocks of proteins, which may have a variety of health benefits. What does the science say?
What is Glycine?
Glycine is one of many amino acids that are used to produce proteins. It is the smallest of all amino acids and is incredibly important for the synthesis of other amino acids, glutathione, creatine, heme, RNA/DNA, and it can also help with the absorption of calcium in the body [1, 2].
Glycine is sometimes called a semi-essential nutrient because it is made by the body, but not in sufficient quantities to supply various tissues (including bone, muscle, and skin) with what they need. Therefore, we need to get quite a bit of glycine from our diets to stay healthy.
The average person usually can make roughly 3g of glycine, and usually consume 1.5 – 3.0 g from food, making their daily intake from roughly 4.5 – 6g .
Some researchers believe that the amount of glycine available in humans might not be enough to meet metabolic needs and that a dietary supplement is appropriate .
One study suggests that humans may fall significantly short of the amount needed for all metabolic uses – by about 10 g per day for a 70 kg (154 lbs) human .
Benefits of Glycine
Despite the presence of glycine in most protein-containing foods, glycine supplements have not been approved by the FDA for medical use and generally lack solid clinical research. Regulations set manufacturing standards for them but don’t guarantee that they’re safe or effective. Speak with your doctor before supplementing.
Possibly Effective For
1) Skin Health
Collagen peptide, which contains a lot of glycine, suppressed UV-B induced skin damage and photoaging .
Women taking 2.5g of collagen peptide for 4 weeks significantly reduced eye wrinkles by 20%, with positive effects lasting after the study ended .
At 8 weeks, collagen significantly improved skin content of procollagen type I by 65%, and elastin by 18%.
Glycine nearly doubles the speed at which skin ulcers heal in 89 diabetic patients across 23 long term care facilities .
Glycine enhanced wound healing in diabetic animal models as well .
Glycine in combination with l-cysteine and dl-threonine topically applied to leg ulcerations significantly improved the degree of wound healing and decreased pain .
2) Mental Illnesses
Glycine supplementation significantly reduced symptoms of schizophrenia .
In treatment-resistant schizophrenia glycine improved cognitive and depressive symptoms (dosed at 0.8g/kg).
The group who made the most improvement were also the most deficient in glycine .
Glycine helps in chronic schizophrenia by increasing NMDA-receptor-mediated neurotransmission .
This effect on NMDA-receptor-mediated neurotransmission allows for glycine to work synergistically with schizophrenia medication .
Glycine supplementation has been shown in one instance over the course of 5 years to significantly reduce symptoms of OCD and body dysmorphic disorder .
Glycine has positive results when used in the treatment of obsessive-compulsive disorder in adults .
Depression is associated with lower levels of blood glycine, as well as high levels of taurine .
3) Brain Health
In rats with alcohol poisoning, glycine was able to reduce the accumulation of cholesterol, free fatty acids, and triglycerides in blood circulation, liver, and brain. Ultimately, this decreases swelling in the brain .
A shortage of glycine in the brain can negatively influence the brain neurochemistry, synthesis of collagen, RNA/DNA, porphyrins, and other important metabolites .
Those who consume regularly low doses of glycine actually reduce damage in future strokes .
The glycine treatment at the dose of 1 – 2g/day was accompanied by a tendency to a decreased risk of dying over 30-days .
Insufficient Evidence For
The following purported benefits are only supported by limited, low-quality clinical studies. There is insufficient evidence to support the use of glycine supplements for any of the below-listed uses. Remember to speak with a doctor before taking glycine supplements, and never use them in place of something your doctor recommends or prescribes.
4) Sleep and Fatigue
Taking glycine before sleep improves sleep quality and sleep efficacy by shortening the time to fall asleep while increasing restorative, slow-wave deep sleep .
After taking glycine for sleep, the following day subjects had lessened daytime sleepiness and improved performance of memory recognition tasks .
Glycine helps improve REM sleep and decrease non-REM sleep .
3g Glycine given to volunteers before sleeping resulted in improvements in fatigue, ‘liveliness and peppiness,’ and ‘clear-headedness’ .
Glycine appears to improve daytime sleepiness and fatigue induced by sleep deprivation .
This effect on the SCN indirectly contributes to reducing sleepiness and fatigue induced by sleep restriction .
5) Gut Health and Ulcers
Glycine dramatically increased the tolerability of Aspirin in the upper GI tract of 20 healthy human volunteers .
Glycine inhibits stomach acid secretion and protects against chemical and stress-induced ulcers .
Glycine possesses significant anti-ulcer activity .
Glycine prevents chemically induced colitis in animal models .
Glycine prevents alcohol-induced stomach lesions (ex. ulcers) when used as a pretreatment in animal models .
In small intestine grafts, glycine improves smooth muscle dysfunction after transplantation as well as reduces inflammation .
Glycine, but not L-arginine, is able to maintain intestinal wall integrity and mucosa in cancer treatment irradiation in animal models .
6) Metabolic Disorders
Glycine is believed to help with diabetes and metabolic disorders .
Glycine intake decreases free fatty acids in blood, fat tissue cell size, and blood pressure in sucrose-fed rats .
Glycine reduces glycated hemoglobin (A1C), a risk factor associated with poor blood glucose management in patients with type 2 diabetes. The dose was 5g/d .
Glycine helps patients with oxidative stress in the development of metabolic syndrome .
7) Glucose Balance & Diabetes
Diabetic patients have 26% lower blood glycine levels than “normal” population .
Glycine can help with positive glucose management by stimulating the production of Glucagon, a hormone which helps potentiate the action of insulin .
These early studies are promising, but larger and more robust human trials are needed.
8) Heart Health
In heart attack conditions (Post-ischaemic reperfusion) glycine prevented the death of heart muscle cells by inhibiting mitochondrial permeability in rats .
9) Joint, Bone, and Muscle Strength
Glycine improved body composition and muscle strength in 8 older men with HIV .
Glycine protected against (peptidoglycan polysaccharide-induced) arthritis in animal studies .
Glycine can potentially help in menopause because of its estrogen-like bone protective effects .
Glycine played a role in maintaining the health of mice suffering from osteoarthritis .
Animal & Cell Research (Lacking Evidence)
No clinical evidence supports the use of glycine for any of the conditions listed in this section. Below is a summary of the existing animal and cell-based research, which should guide further investigational efforts. However, the studies listed below should not be interpreted as supportive of any health benefit.
Glycine acts directly on inflammatory cells to suppress the activation of transcription factors, the formation of free radicals, and inflammatory cytokines .
In this same study, glycine fed rats who had liver damage and also injected with a toxin had an 83% survival rate, whereas the non-glycine control group had 0% rate of survival .
In mice fed with various types of sugar, TNF-alpha is significantly higher in mice fed fructose .
Glycine has protective properties against the harms of Fructose by its ability to prevent the release of inflammatory cytokines (TNF-α, IL-6) release with fructose exposure .
11) Liver Health
In rats with alcohol poisoning, feeding glycine reduced accumulation of cholesterol, phospholipids, free fatty acids and triglycerides in blood circulation, liver, and brain, ultimately reversing liver disorder associated with fat accumulation .
Glycine reduced liver damage and decreases mortality rates in rats suffering from a serious bacterial infection (sepsis) .
Supplementation of glycine for five days in animal models prior to complete or partial liver donation significantly inhibited liver injury and liver-related enzymes .
Glycine maintains mitochondrial activity and bile composition in liver injury in animals .
12) Alcohol Absorption
Blood alcohol levels were significantly lower in animals which had consumed glycine prior to intoxication over controls who had not .
Glycine reduced the rate at which the stomachs of mice absorbed alcohol and emptied into the intestine .
13) Kidney Health
Kidney tubes (proximal tubules) are resistant to oxygen deprivation damage if glycine is present in the test tube. This has only been observed in an isolated tissue study, and studies in animals and humans are lacking, so we can’t say what the implication is for kidney health in a living system .
14) Oral Health
In rat models, supplementation with 4% glycine caused a 65.7% reduction of cavity occurrence. This has not been investigated in humans .
15) Thyroid Hormones
Glycine might also increase the conversion of T4 to T3 in the liver, but this effect has only been studied in fish so far. It is unclear whether or how much this result might apply to human livers .
Supplementing With Glycine
Note that there is no safe and effective dose because no sufficiently powerful and specific study has been conducted to determine one. That being said, many human trials have safely used doses between 1 g per day (for supporting brain health after a stroke) to over 50 g (for schizophrenia).
Most Americans get between 1.5 and 3 g of glycine from food, and our bodies produce another 3 g or so.
Many commercial supplements come in 1 g capsules or in free powder that can be scooped into shakes or other fluids.
Side Effects of Glycine
Slight sedation is a possible side effect of taking Glycine . Some practitioners recommend taking it in the evening for this reason.
Potential Downsides of Glycine
In a Japanese study of nearly 30,000 patients, the risk of dying after stroke may be increased by meat consumption. The scientists pointed out a correlation between glycine intake and mortality from stroke, though they did not suggest a reason for this link .
Glycine is not recommended to take while suffering from diarrhea. It may worsen the condition and lead to poor rehydration .
Top Foods with The Highest Glycine Content
You can get a good amount of glycine from glycine, collagen or gelatin.
A list of foods high with glycine:
- Soy Protein Isolate
Collagen contains 22 – 30% glycine. Adding 1 – 2 tbsp a day to a breakfast smoothie will give you an additional 2.5 – 3.5g glycine per Tbls.
Glycine is a semi-essential amino acid, meaning that the human body can produce some on its own, though some must also be consumed in food. The smallest of the amino acids, it is important for the production of many proteins and compounds, including DNA and RNA.
Glycine supplementation may prove useful for diabetic ulcers, schizophrenia, and stroke recovery. Other human studies suggest a potential benefit for other areas of metabolic and mental health, including insulin resistance, insomnia, and sleep disorders.
The richest dietary sources of glycine include gelatin, fish, and all types of meat. Glycine is also available as a dietary supplement.