Glycine
Summary
A nonessential amino acid. Small Japanese RCTs using 3 g before bed report improved subjective sleep quality and reduced next-day sleepiness, including one trial with polysomnographic measurements.
Mechanism
Glycine is a nonessential amino acid and an inhibitory neurotransmitter. The proposed mechanism is action on NMDA receptors in the suprachiasmatic nucleus, the brain's circadian pacemaker, promoting peripheral vasodilation and a drop in core body temperature, a physiological change that normally accompanies sleep onset.
Reported effects
Ratings are relative to peers in the same category, not absolute claims.
Studied dosing: research context
Published trials used 3 g taken 30-60 minutes before bedtime, for 2-4 nights in most studies. These are doses used in research, not guidance.
Research context only. This is not a recommendation.
Safety
No serious adverse events were observed at 3 g in published trials. A small safety study at 9 g reported only mild, transient digestive symptoms (soft stool, stomach discomfort) and no carryover daytime sleepiness. Data in pregnancy are limited.
Limitations
Trials are very small (mostly under 20 participants) and short, and all come from the same research group with ties to a glycine manufacturer. Independent replication in larger, longer trials is missing, and effects on objective sleep architecture are minimal.
References
- Yamadera et al., Sleep Biol Rhythms (2007) - glycine ingestion and subjective sleep quality with polysomnography
- Inagawa et al., Sleep Biol Rhythms (2006) - subjective effects of glycine ingestion before bedtime
- Bannai et al., Front Neurol (2012) - glycine and daytime performance in sleep-restricted volunteers