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Glycine and sleep

A substantial number of our posts so far have been focusing on the essential or semi-essential amino acids which are not sufficiently synthetized within mammalian bodies. Dietary supplementation with those amino acids in specific situations makes intuitive sense. But, the word “non-essential” is misleading and in many cases they can provide “very essential” support to our organism. Let’s look even at the simples non-essential amino acid – glycine. Glycine has only tiny hydrogen on its side-chain and thus it is the smallest of the twenty amino acids that build natural proteins. A typical diet contains about 2 grams of glycine daily. The primary sources are protein-rich foods including meat, fish and legumes. Glycine is used as a part of nutritional treatments in diseases such as schizophrenia or benign prostatic hyperplasia (BPH). It is also used to protect kidneys from the harmful side effects of certain drugs used after organ transplantation. What about regular healthy population? Recent clinical studies have shown that glycine dietary supplementation (3 gram) can help to improve sleep quality and mental performance on the following morning – especially in slightly sleep-deprived people www.ncbi.nlm.nih.gov/pubmed/22529837.

Interestingly, while improving sleep and shortening time between going to bed and falling asleep, glycine did not significantly affect either plasma melatonin concentration before or during the night, or the expression of “circadian clock genes” such as Bmal1 and Per2. However, glycine induced an increase in the neuropeptides arginine vasopressin and vasoactive intestinal polypeptide in the light period and probably promoted sleep also via peripheral vasodilatation through the activation of NMDA receptors in the suprachiasmatic nucleus (a part of the central nervous system). www.ncbi.nlm.nih.gov/pubmed/25533534. Moreover, glycine reduced slightly core body temperature before and during sleep, which is also a very important aspect of sleep regulation since the start of sleep is known to involve a decrease in the core body temperature www.ncbi.nlm.nih.gov/pubmed/22293292.

In terms of safety, nine grams of glycine (single ingestion) were demonstrated to be safe in adult humans (Inagawa et al., “Seikatsu Eisei” 2006, 50(1), 27-32), which is to be expected considering innate production and intake of glycine from foods. Taken together, the smallest amino acid makes a potentially big contribution to improving our quality of life and it does not look so “small” anymore in my eyes! Indeed, successful glycine supplements that are based on the above clinical science, are already being marketed in Japan to improve sleep.