Glycine is the simplest of the 20 different amino acids used as building blocks to make proteins for your body. It works in concert with glutamine, a substance that plays a major role in brain function. Glycine has shown some promise as an aid in the treatment of
Your body is able to make glycine using another amino acid, serine. Because you can manufacture glycine, you don't really have to consume any, so it's called a "nonessential amino acid." Most of us get about 2 g of glycine a day from the foods we regularly eat anyway. This dietary glycine comes mostly from high-protein foods like meat, fish, dairy products, and legumes. For treating certain disease conditions, however, much larger amounts than are normally consumed have been advocated; such high doses can only be obtained by taking supplements.
Dosages of oral glycine used in clinical trials for therapeutic purposes range from 2 to 60 g daily.
Several studies have evaluated glycine as a supportive treatment for
A small double-blind study found evidence that glycine may help improve long-term blood sugar control in people with type 2 diabetes.
Glycine alone and in combination with other amino acids has shown a bit of promise for enhancing wound healing.
Other studies in laboratory animals suggest that dietary glycine may prevent tumor formation and growth in the livers of mice and rats.
Manufacturers advertising glycine supplements have made a number of additional claims for it, including prevention of
Because it has a sweet taste, glycine has also been recommended as a sugar substitute for people with diabetes.
What Is the Scientific Evidence for Glycine?
Glycine might enhance the effectiveness of drugs used for
, especially those in the older
Phenothiazine drugs are most effective for the "positive" symptoms of schizophrenia, such as hallucinations and delusions. (Such symptoms are called "positive" because they indicate the presence of abnormal mental functions, rather than the absence of normal mental functions.) In general, however, these medications are less helpful for the "negative" symptoms of schizophrenia, such as apathy, depression, and social withdrawal. Glycine might be of benefit here.
A double-blind, placebo-controlled trial enrolled 22 participants who continued to experience negative symptoms of schizophrenia despite standard therapy.
Three earlier double-blind, placebo-controlled clinical trials of glycine together with standard drugs for schizophrenia also found it to be helpful for negative symptoms.
The trials just discussed were conducted before atypical antipsychotics were widely available. These drugs cause fewer side effects and also provide benefits for the negative symptoms of schizophrenia along with the positive. One study found that glycine augmented the effectiveness of two of these drugs: olanzapine and risperidone.
Glycine's potential usefulness for treating individuals who have undergone
Although other researchers using glycine for brain disorders have reported that such small doses of glycine would not be sufficient to cross the blood-brain barrier,
No serious adverse effects from using glycine have been reported, even at doses as high as 60 g per day. One participant in the 22-person trial described above developed stomach upset and vomiting, but it ceased when the glycine was discontinued.
In contradiction to the study on strokes mentioned above, theoretical concerns have been raised that suggest glycine might actually increase brain injury in strokes. 19
In addition, as noted above, it is possible that use of glycine could reduce the benefits of clozapine.
Maximum safe doses for young children, pregnant or nursing women, or people with liver or kidney disease are not known.
Interactions You Should Know About
If you are taking:
2. Heresco-Levy U, Javitt DC, Ermilov M, et al. Double-blind, placebo-controlled, crossover trial of glycine adjuvant therapy for treatment-resistant schizophrenia. Br J Psychiatry . 1996;169:610-617.
8. Fries MH, Rinaldo P, Schmidt-Sommerfeld E, et al. Isovaleric acidemia: response to a leucine load after three weeks of supplementation with glycine, L-carnitine, and combined glycine-carnitine therapy. J Pediatr . 1996;129:449-452.
9. Itoh T, Ito T, Ohba S, et al. Effect of carnitine administration on glycine metabolism in patients with isovaleric acidemia: significance of acetylcarnitine determination to estimate the proper carnitine dose. Tohoku JExp Med . 1996;179:101-109.
12. Sopala M, Schweizer S, Schafer N, et al. Neuroprotective activity of a nanoparticulate formulation of the glycineB site antagonist MRZ 2/576 in transient focal ischaemia in rats. Arzneimittelforschung . 2002;52:168-74.
20. Tatlisumak T, Takano K, Meiler MR, Fisher M. A glycine site antagonist ZD9379 reduces number of spreading depressions and infarct size in rats with permanent middle cerebral artery occlusion. Acta Neurochir Suppl . 2000;76:331-333.
24. Martinez-Abundis E, Kam-Ramos AM, Hernandez-Salazar E, Gonzalez-Ortiz. Effect of glycine on insulin secretion, fasting and postprandial glucose levels in patients with type 2 diabetes mellitus. 18th International Diabetes Federation Congress, Paris, August 24-29, 2003;abstract 758.
25. Diaz P, Bhaskara S, Dursun SM, et al. Double-blind, Placebo-Controlled, Crossover Trial of Clozapine Plus Glycine in Refractory Schizophrenia Negative Results. J Clin Psychopharmacol . 2005;25:277-278.
26. . Buchanan RW, Javitt DC, Marder SR, et al. The cognitive and negative symptoms in schizophrenia trial (CONSIST): the efficacy of glutamatergic agents for negative symptoms and cognitive impairments. Am J Psychiatry. 2007;164:1593-1602.
Last reviewed April 2009 by EBSCO CAM Review Board
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