Research indicates that a lack of glycine in the diet may contribute to difficulty sleeping. Initial studies have shown that people supplementing with 3 grams of glycine before bed fall asleep faster, have enhanced sleep quality, experience less daytime sleepiness, and actually feel more alert the following day.^{2 3}

Glycine can act in several ways to support sleep. One study showed that oral glycine increased serotonin in rats; serotonin is then converted to melatonin, the “sleep” hormone.⁴ Glycine, along with GABA, also acts on the central nervous system by inhibiting the skeletal muscles during sleep, allowing us to dream and experience REM sleep without moving about in our beds.³

Several researchers believe that glycine’s primary effect on sleep physiology is helping maintain a lower core body temperature during sleep.^{5 6} During healthy sleep, the body’s temperature naturally decreases during the night, and if for some reason this core temperature rises, it can cause us to wake. Have you ever noticed waking up and feeling hot? 

In addition to promoting healthy sleep, research has found that glycine has antioxidant and anti-inflammatory actions and is protective of the liver. It can also improve metabolic disorders in people with cardiovascular disease, inflammatory diseases, diabetes, and obesity. It also plays a role in neurotransmission and is necessary to activate receptors in the brain related to learning, memory, and cognition.^{7 8}

So why might you be deficient in glycine? One of glycine’s primary jobs is to manufacture connective tissue, including collagen. The body makes three grams a day but needs about 15 grams daily to rebuild collagen and other tissues. Traditionally dietary glycine comes from food sources like collagen found in the bones, joints, and skin of animal products—foods that are not readily consumed in our modern diet. So, if you are not eating chitlins, cracklins, and gizzards regularly and/or making homemade bone broth, you may want to consider supplementing with glycine. How much you ask? One study used three grams of pure glycine before bedtime. Jonathan Wright, MD, medical director of the Tahoma Clinic in Washington, suggests aiming for ten grams a day to restore glycine levels in the body. His favorite way to take it is by mixing glycine powder with purified gelatin and some healthy flavorings (chocolate, fruit, etc.) to make a dessert pudding.⁹ He recommends gelatin since it also contains a high amount of glycine (approximately 30%) along with a balance of other naturally occurring amino acids.

As many of us struggle with getting enough sleep, it is nice to know that there is an additional tool that we can use to unlock the mystery of a restful night’s sleep.

A Word of Caution Regarding Glycine and Cancer

Cancer patients with active tumors should exercise caution in using glycine. Research indicates that certain cancer cells may proliferate rapidly by preferentially utilizing glycine as an energy source.¹⁰ Please work closely with your doctor if you have or have had cancer before supplementing with glycine.

References

1. Adjaye-Gbewonyo, D., Ng, A. E., & Black, L. I. (2022). Sleep Difficulties in Adults: United States, 2020. https://doi.org/10.15620/cdc:117490
2. Inagawa, Kentaro, et al. “Subjective Effects of Glycine Ingestion before Bedtime on Sleep Quality - Sleep and Biological Rhythms.” SpringerLink, Springer Japan, 28 July 2016, link.springer.com/article/10.1111/j.1479-8425.2006.00193.x  . 
3. Yamadera, W., Inagawa, K., Chiba, S., Bannai, M., Takahashi, M., & Nakayama, K. (2007). Glycine ingestion improves subjective sleep quality in human volunteers, correlating with polysomnographic changes. Sleep Biol. Rhythms 5, 126–131 https://doi.org/10.1111/j.1479-8425.2007.00262.x
4. Bannai, M., Kawai, N., Nagao, K., Nakano, S., Matsuzawa, D., & Shimizu, E. (2011). Oral administration of glycine increases extracellular serotonin but not dopamine in the prefrontal cortex of rats. Psychiatry and clinical neurosciences, 65(2), 142–149. https://doi.org/10.1111/j.1440-1819.2010.02181.x
5. Bannai, M., & Kawai, N. (2012). New therapeutic strategy for amino acid medicine: glycine improves the quality of sleep. Journal of pharmacological sciences, 118(2), 145–148. https://doi.org/10.1254/jphs.11r04fm
6. Kawai, N., Sakai, N., Okuro, M., Karakawa, S., Tsuneyoshi, Y., Kawasaki, N., Takeda, T., Bannai, M., & Nishino, S. (2015). The sleep-promoting and hypothermic effects of glycine are mediated by NMDA receptors in the suprachiasmatic nucleus. Neuropsychopharmacology : official publication of the American College of Neuropsychopharmacology, 40(6), 1405–1416. https://doi.org/10.1038/npp.2014.326
7. 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. doi: 10.1155/2017/1716701. 
8. Aguayo-Cerón KA, Sánchez-Muñoz F, Gutierrez-Rojas RA, Acevedo-Villavicencio LN, Flores-Zarate AV, Huang F, Giacoman-Martinez A, Villafaña S, Romero-Nava R. Glycine: The Smallest Anti-Inflammatory Micronutrient. Int J Mol Sci. 2023 Jul 8;24(14):11236. doi: 10.3390/ijms241411236.
9. Wright, J.V. (n.d.). The 50¢ a day anti-aging supplement could have you turning back the  hands of time starting today—and sleeping like a baby tonight. Nutrition and Healing, 19(12). 
10. Jain, M., Nilsson, R., Sharma, S., Madhusudhan, N., Kitami, T., Souza, A. L., Kafri, R., Kirschner, M. W., Clish, C. B., & Mootha, V. K. (2012). Metabolite profiling identifies a key role for glycine in rapid cancer cell proliferation. Science (New York, N.Y.), 336(6084), 1040–1044. https://doi.org/10.1126/science.1218595