Glycine

Glycine is the smallest and simplest proteinogenic amino acid with numerous metabolic functions. It is not essential and has no L or D form due to its simple structure. Glycine accounts for 11.5% of the total amount of amino acids in the body. Glycine is particularly abundant in collagen, the structural protein of connective tissue. Due to its small size, glycine enables the structure of the triple helix and is therefore an important component of bones, teeth, skin and tendons. (1)
Furthermore, the amino acid is directly involved in the purine formation of DNA and RNA, plays a central role in the synthesis of heme and an important neurotransmitter in the central and peripheral nervous system.
Creatine, which is mainly found in muscle tissue and serves as an energy reserve, is also produced from glycine. Glycine is also a component of glutathione and contributes to antioxidative process. (2)

Glycine is found in animal and plant foods. The amino acid is particularly strongly represented in fish, meat and poultry. Good vegetable glycine sources include soybeans, lentils, oat flakes and peanuts. (3)

Glycine acts in the central nervous system as an inhibitory neurotransmitter. By binding endogenously synthesized glycine to the glycine receptors, channels are opened, resulting in inhibition of neuronal functions and a calming effect. (4)
Supplementation of 3g glycine per day significantly improves sleep quality and has a positive effect on sleepiness, fatigue and daytime performance. (5)
Orally administered glycine is thought to act as a co-agonist via the NMDA receptors (ionotropic glutamate receptors) of the suprachiasmatic nucleus (SCN). Supplemented glycine can accumulate in the brain, the concentration level of glycine in blood and cerebrospinal fluid is in turn associated with a drop in body temperature due to dilation of the blood vessels. A lower body temperature is observed during falling asleep and also during sleep. (6)
Furthermore, it is assumed that glycine modulates SCN functions and thus influences the circadian rhythm. The effects of SCN on the sleep-wake rhythm and the sleep-promoting potential of glycine are based on various mechanisms that have not yet been adequately investigated. (5)

Glycine appears to exert several protective effects, including anti-inflammatory, immunomodulatory and direct cytoprotection.

Glycine has a macrophage-like effect on inflammatory cells. It suppresses the activation of transcription factors, the formation of free radicals and inflammatory cytokines. (7)

In numerous studies, glycine has been shown to have a protective effect in various tissues such as the kidneys, liver and lungs. (7) (8)

The protective, synergistic mechanisms of glycine are not yet fully understood. However, the presence of glycine receptors has been demonstrated in many inflammatory cells. Glycine can suppress increased intracellular calcium levels via these receptors. These in turn are induced by a variety of events, such as the production of cytokines and other inflammatory mediators. In addition, glycine can reduce ROS production (reactive oxygen species) in various ways and influence the integrity of cell membranes by inhibiting e.g. phospholipase A2 and other degrading enzymes whose activation can lead to cell damage. The controversially discussed mechanisms are numerous and still insufficiently researched, however, a beneficial effect of glycine on inflammatory, immunoloinflammatory and cytotoxic events seems to be well documented. (7)

In animal experiments, hepatoprotective properties of glycine are shown in alcoholic liver damage and drug-induced liver stress. Glycine is successfully used here to support detoxification processes. It can optimize the lipid level in alcohol abuse and thus contribute to the maintenance of membrane integrity. Glycine supplementation reduces the alcohol level in the blood and the accumulation of free fatty acids in the liver and brain. (9) At the same time, the oxidative stress mediated by free radicals in the membranes of erythrocytes, plasma and hepatocytes can also be positively influenced. (10)

1) Yan, B. X. et al. 1997. Glycine residues provide flexibility for enzyme active sites. Journal of Biological Chemistry. 272(9):3190–3194.

2) Mel´endez-Hevia, E. et al. 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.

3) Souci SW. et al. Die Zusammensetzung der Lebensmittel, Nährwert-Tabellen, 7. überarbeitete Auflage. medpharm Scientific Publisher, Stuttgart 2008.
4) Rajendra, S. et al. 1997. The glycine receptor. Pharmacol Ther. 73:121–146.

5) Bannai, M. et al. 2012. The effects of glycine on subjective daytime performance in partially sleep-restricted healthy volunteers. Front Neurol. 3:61.

6) Kawai, N. et al. 2015. The sleep-promoting and hypothermic effects of glycine are mediated by NMDA receptors in the suprachiasmatic nucleus. Neuropsychopharmacology. 40(6):1405–16

7) Zhong, Z. et al. 2003. L-glycine: a novel antiinflammatory, immunomodulatory, and cytoprotective agent. Current Opinion in Clinical Nutrition and Metabolic Care 6(2):229–240.

8) Howard, A. et al. 2010. Glycine transporter GLYT1 is essential for glycine-mediated protection of human intestinal epithelial cells against oxidative damage. J Physiol 588.6:995–1009.

9) Senthilkumar, R. et al. 2004. Glycine modulates lipids and lipoproteins levels in rats with alcohol induced liver injury. Internet Journal of Pharmacology. 2(2).
10) Senthilkumar, R. et al. 2004. M. Protective effect of glycine supplementation on the levels of lipid peroxidation and antioxidant enzymes in the erythrocyte of rats with alcohol-induced liver injury. Cell Biochemistry and Function. 22(2):123–128.
11) Arreortua Noe, S. et al. 2013. Effect of Glycine on Protein Oxidation and Advanced Glycation End Products Formation. Journal of Experimental&Clinical Medicine 5(3):109-114.
12) Singh, R. et al. 2001. Advanced glycation end-products: a review.Diabetologia 44(2):129-46.

References Interactions

Burgerstein, U.P. et al. Handbuch Nährstoffe: Vorbeugen und heilen durch ausgewogene Ernährung: Alles über Spurenelemente, Vitamine und Mineralstoffe, 12. Auflage. Trias Verlag Stuttgart, 2012

Biesalski, H.K. et al. Taschenatlas Ernährung. 4. Auflage. Georg Thieme Verlag Stuttgart, 2007

Löffler G, Petrides P, Heinrich P: Biochemie & Pathobiochemie, 8. Auflage, Springer Medizin Verlag Heidelberg, 2007