Glycine supplementation was also shown to improve insulin responses.
Writing in GeroScience, a group of researchers from the Centre for Healthy Longevity at Singapore’s National University Health System (NUHS) assessed the effects of glycine oral supplementation in both healthy and diseased populations.
The effects of glycine supplementation on multiple health areas such as the endocrine, metabolic, nervous, cardiovascular, and immune system were studied.
A total of 50 human clinical studies found on Embase, PubMed, Web of Science, and Cochrane were included in this review.
Most of them, 42 studies, were randomised controlled trials.
Out of the 50 studies, 18 involved healthy populations while 34 involved diseased population.
The mean age of the participants was between 21.5 and 41.4 for the healthy population and between 29.5 and 67 for the diseased population.
In these studies, glycine was taken orally by the healthy and diseased populations for up to 14 days and four months respectively.
One of the major findings was that glycine supplementation could benefit the nervous system in both healthy and diseased populations.
Among the healthy population, improvements in sleep quality, alertness, cognition, and decreased fatigue and sleepiness were reported in studies conducted by Bannai M et al, Yamadera et al, and Inagawa K et al.
In this case, the participants received glycine supplementation at three grams per day at 30 mins to one hour before bedtime for two to four days.
“The positive effects reported on healthy populations included improved sleep and decreased daytime fatigue and improved insulin responses,” said the researchers from NUHS.
They explained that the benefits were due to the action of glycine on the N-Methyl-D-Aspartate (NMDA) receptors in the suprachiasmatic nucleus (SCN), which is the master circadian pacemaker, by promoting hypothermia and vasodilation.
“One possible mechanism by which glycine may confer its geroprotective effects may be through its action on NMDA receptors; although further research is required to understand the chronotherapeutic and tissue-specific effects of such an interaction and the interplay between multiple physiological systems in healthy and diseased populations.”
High single dose showed negative effects
However, negative effects in cognitive performance were reported in studies that gave a higher dose of glycine in a single bolus.
Specifically, a single bolus of glycine taken at 0.8 grams per kilograms body weight orally, or 200mg per kg body weight intravenously, had showed negative effects on sensorimotor gating and cognitive performance in healthy populations.
Sensorimotor gating is a normal protective mechanism in the brain that filter irrelevant sensory stimulation. A dysfunctional sensorimotor gating could result in stimulus overload and the misinterpretation of sensory information.
Larger and long-term studies with more robust study designs are needed to study the effects of glycine, especially its potential as a geroprotector, in the healthy populations, said the researchers.
They said that animal models have showed that glycine administration could extend the lifespan of C. elegans by up to 33 per cent, and of rats by approximately 20 per cent, and mice by six per cent.
“Although the administration of glycine may improve the characteristics of multiple physiological systems, there is currently limited evidence supporting their preventative effect for healthy populations, which warrants the need for future research.
“Importantly, larger and more robustly designed RCTs are necessary to strengthen the current evidence on the potential of glycine administration in conferring benefits in adult humans.
“Given that glycine is inexpensive and likely safe for administration through oral supplementation, it is important to study its potential lifespan and healthspan enhancing properties as a geroprotector.”
Glycine’s effects on diseased population
Glycine supplementation has also shown improved symptoms among diseased populations, such as the psychiatric patients.
For instance, glycine supplementation between 0.2 and 0.8 grams per kilogram body weight daily over six to 12 weeks had improved schizophrenic / psychiatric symptoms, as well as extrapyramidal symptoms or involuntary movements, and cognition.
“The majority of the physiological systems demonstrated significant positive effects on glycine that were mostly related to the nervous system with longer-term glycine administration, especially in diseased populations afflicted with psychiatric illnesses such as Schizophrenia,” said the researchers.
On the other hand, sleep latency or the time taken to fall alseep, had decreased in individuals with an overactive bladder with three grams of oral glycine supplementation twice per day over four weeks.
The effect of glycine administration on the characteristics of physiological systems in human adults: A systematic review
Authors: J. Soh · Z. X. Lim · J. Goh · B. K. Kennedy · A. B. Maier