L-Glycine is one of the many amino acids that work as a protein builder in the human body. Glycine 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, a bone-forming mineral that accounts for 60% of bones, in the body. 

L-Glycine helps to improve natural growth hormone production. According to the study on the stimulatory effect of glycine on human growth hormone secretion, in the normal subjects, a clear and significant increase of serum human growth hormone (HGH) level was observed. A more pronounced and significant increase of HGH value in serum was also found in the subjects with gastrectomy. (1) The facts demonstrated that glycine is one of the stimulatory agents inducing the pituitary gland to secrete HGH. 

L-Glycine benefits the skeletal muscles and tissues by promoting development and boosting structural integrity. Glycine increases creatine levels in the muscle and regulates fat metabolism in the muscles and thus assists in controlling the energy expenditure. In one study in 8 elderly men with HIV, Glycine improved body composition and muscle strength. (2) Also, MicroCT-analysis showed that glycine significantly enhanced bone mineral density, trabecular number, and connectivity density in OVX mice. (3) 

L-Glycine supports healthy sleep patterns which are important factors in height growth. 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 reduced daytime sleepiness and improved the performance of memory recognition tasks. (4) Fischer’s LSD test revealed that glycine ingestion on the previous night significantly improved the performance of the memory recognition task. 

Glycine also has a positive effect on brain health. A study has shown small amounts of glycine dilate the microvessels in the brain by up to 250%. (5) Another study has shown a shortage of glycine can negatively influence brain neurochemistry and the synthesis of collagen, nucleic acids, porphyrins, and other important metabolites. (6) Glycine also helps the prevention and recovery of stroke. For example, regular consumption of low dose levels of glycine actually reduces damage in future strokes. (7) In addition, in ischemic stroke patients, taking glycine 1-2 g per day increased GABA concentrations, a natural ingredient that helps the secretion of growth hormones, and normalized autoantibodies, reduced glutamate, aspartate levels, and lipid peroxidation. (8) 

In addition, glycine can help with heart health and the prevention of diabetes. Systolic blood pressure (SBP) showed a significant decrease in glycine-treated men. In heart attack conditions (Post-ischaemic reperfusion) glycine prevented the death of heart muscle cells by inhibiting mitochondrial permeability in rats. (9, 10) In addition, Glycine stimulates the secretion of a gut hormone (glucagon) that helps insulin remove glucose from circulation. (11) Another research revealed the fact that diabetic patients had 26% lower blood glycine levels than the control group. (12) 

References: 

1. Kasai K, Kobayashi M, Shimoda SI. Stimulatory effect of glycine on human growth hormone secretion. Metabolism. 1978 Feb; 27 (2): 201-8. 

2. Nguyen D, Hsu JW, Jahoor F, Sekhar RV. Effect of increasing glutathione with cysteine and glycine supplementation on mitochondrial fuel oxidation, insulin sensitivity, and body composition in older HIV-infected patients. J Clin Endocrinol Metab. 2014 Jan; 99 (1): 169-77. 

3. Kim MH, Kim HM, Jeong HJ. Estrogen-like osteoprotective effects of glycine in in vitro and in vivo models of menopause. Amino Acids. 2016 Mar; 48 (3): 791-800. 

4. Wataru YAMADERA, Kentaro INAGAWA, Shintaro CHIBA, Makoto BANNAI, Michio TAKAHASHI, Kazuhiko NAKAYAMA. Glycine ingestion improves subjective sleep quality in human volunteers, correlating with polysomnographic changes Sleep and Biological Rhythms. 2007 Mar; 5 (2): 126-131.

5. Podoprigora GI, Nartsissov YR, Aleksandrov PN. Effect of glycine on microcirculation in pial vessels of rat brain. Bull Exp Biol Med. 2005 Jun; 139 (6): 675-7. 

6. Badenhorst CP, Erasmus E, van der Sluis R, Nortje C, van Dijk AA. A new perspective on the importance of glycine conjugation in the metabolism of aromatic acids. Drug Metab Rev. 2014 Aug; 46 (3): 343-61. 

7. Gusev EI, Skvortsova VI, Dambinova SA, Raevskiy KS, Alekseev AA, Bashkatova VG, Kovalenko AV, Kudrin VS, Yakovleva EV. Neuroprotective effects of glycine for therapy of acute ischaemic stroke. Cerebrovasc Dis. 2000 Jan-Feb; 10 (1): 49-60. 

8. Gusev EI, Skvortsova VI, Dambinova SA, Raevskiy KS, Alekseev AA, Bashkatova VG, Kovalenko AV, Kudrin VS, Yakovleva EV. Neuroprotective effects of glycine for therapy of acute ischaemic stroke. Cerebrovasc Dis. 2000 Jan-Feb;10 (1): 49-60. 

9. Díaz-Flores M, Cruz M, Duran-Reyes G, Munguia-Miranda C, Loza-Rodríguez H, Pulido-Casas E, Torres-Ramírez N, Gaja-Rodriguez O, Kumate J, Baiza-Gutman LA, Hernández-Saavedra D. Oral supplementation with glycine reduces oxidative stress in patients with metabolic syndrome, improving their systolic blood pressure. Can J Physiol Pharmacol. 2013 Oct; 91 (10): 855-60. 

10. Ruiz-Meana M, Pina P, Garcia-Dorado D, Rodríguez-Sinovas A, Barba I, Miró-Casas E, Mirabet M, Soler-Soler J. Glycine protects cardiomyocytes against lethal reoxygenation injury by inhibiting mitochondrial permeability transition. J Physiol. 2004 Aug 1; 558 (Pt 3): 873-82. 

11. Gannon MC, Nuttall JA, Nuttall FQ. The metabolic response to ingested glycine. Am J Clin Nutr. 2002 Dec; 76 (6): 1302-7. 

12. Fiehn O, Garvey WT, Newman JW, Lok KH, Hoppel CL, Adams SH. Plasma metabolomic profiles reflective of glucose homeostasis in non-diabetic and type 2 diabetic obese African-American women. PLoS One. 2010 Dec 10; 5 (12): e15234.