Glycine

Research summary

• The most established use of glycine alone is sleep: real controlled studies and reviews find glycine taken before bed improves subjective sleep quality and reduces daytime sleepiness after partial sleep restriction, though the evidence base for this specific effect is relatively small.
• The more striking recent evidence comes from combining glycine with N-acetylcysteine (GlyNAC) rather than glycine alone: a randomized clinical trial and an earlier pilot trial in older adults found GlyNAC supplementation improved glutathione deficiency, oxidative stress, mitochondrial function, inflammation, and physical function — several biological hallmarks associated with aging.
• This is genuinely promising but still early-stage: the supporting trials are few and relatively small, come substantially from one research group, and test a glycine-plus-NAC combination rather than glycine on its own, so it would be an overstatement to attribute these aging-related effects to glycine alone without further independent replication.