What is glycine?

If you remember chemistry or biochemistry from high school, the word glycine might ring a bell. If not, read on to answer the question: what is glycine?

What is glycine?

Glycine is the simplest amino acid. Amino acids are chemical compounds that contain an amino group (NH₂) and carboxyl group (-COOH). The chain between is composed of carbon and hydrogen atoms and its length defines the amino acid. Amino acids are the building blocks of all proteins.

Amino acids are normally categorised in non-essential (produced by our bodies) and essential (which must be consumed in our diets). Glycine is a non-essential amino acid; however to be more exact it should be classified as conditionally essential because it is required to some degree in certain life stages, such as growth.

Glycine is 11.5% of the amino acids in the body. In growing humans, 80% of glycine is used for protein synthesis (1).

Functions of glycine

Glycine is important for immune function, growth and nutrient metabolism (1).

Neurotransmission, inflammation, etc.

The most well-known role of glycine is as a neurotransmitter (2, 3). It has also been studied as an anti-inflammatory under certain circumstances, such as injury and transplantation (1, 2, 3) and potentially lower the increase in free fatty acids (2, 3).

Other potential benefits of glycine include protection against the harmful effects of alcohol metabolites in the liver, protection against stomach injuries and ulcers and supression of cell proliferation (1).

Sleep

Perhaps the most interesting application of glycine is on sleep. As we know, sleep is a fundamental part of life as it allows for cellular cleaning, memory consolidation, immune function, recovery from exercise, etc.

Animal and human studies have explored the use of supplemental glycine to improve sleep. The proposed mechanisms include the decrease in core body temperature, increase in vasodilation (2, 3) and increase in the release of serotonin (2).

Although human studies are small, they seem to indicate that glycine supplementation improves subjective ratings of sleepiness and fatigue and, most importantly, quality of sleep as measured by psychomotor and memory tasks (3, 4). Studies have also shown that supplementation in higher doses of up to 9g do not have detrimental effects not cause sleepiness during the day (2, 3).

Where do we get glycine from

Every day we make approximately 45g of glycine in our bodies and get between 3 and 5 g from our diet (2, 3).

Dietary sources of glycine include gelatin, collagen, animal foods such as red meats, chicken, fish and seafood and protein powders. Below is a graph showing the amount of glycine in selected foods (those with 1 gram or more of glycine per 100g of food). The data shown comes from FoodData Central (5). Hover over the food names or dots to see more information.

Note that, while the relative content of glycine in some foods is high, in reality you would not consume 100g of protein powder or wheat germ in one seating. You would, however, consume 100g or more of meat, fish or chicken.

Another great source of glycine is collagen peptides. The products I typically use and recommend contain between 2.1 and 3.7 grams of glycine per serve (18.6 to 22.7g per 100g).

Finally, you can also consume glycine as a supplement on its own. It comes as a fine white powder which is sweet and should be consumed dissolved in water.

Summary and recommendations

Glycine has several important roles in the body. As a conditionally essential amino acid, the amount needed for normal body functions is produced endogenously. However, supplementation can help to reduced inflammation under certain circumstances, prevent alcohol-induced liver injury, prevent gastric ulcers and improve sleep.

If you choose to try a glycine supplement instead of relying on food sources to improve sleep:

• Look for a reputable brand, especially if you are a drug-tested competing athlete
• Experiment with the recommended dose of 3g dissolved in water within 1 hour of going to bed

References

1. Razak MA, Begum PS, Viswanath B, Rajagopal S. Multifarious Beneficial Effect of Nonessential Amino Acid, Glycine: A Review. Oxid Med Cell Longev. 2017;2017:1716701.
2. Bannai M, Kawai N. New therapeutic strategy for amino acid medicine: glycine improves the quality of sleep. Journal of pharmacological sciences. 2012;118(2):145-8.
3. Bannai M, Kawai N, Ono K, Nakahara K, Murakami N. The effects of glycine on subjective daytime performance in partially sleep-restricted healthy volunteers. Frontiers in neurology. 2012;3:61.
4. Yamadera W, Inagawa K, Chiba S, Bannai M, Takahashi M, Nakayama K. Glycine ingestion improves subjective sleep quality in human volunteers, correlating with polysomnographic changes. Sleep and Biological Rhythms. 2007;5(2):126-31.
5. U.S. Department of Agriculture, Agricultural Research Service. FoodData Central, 2019. fdc.nal.usda.gov.

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