Nonessential amino acid
Glycine
Limited evidenceThe simplest amino acid, a major part of collagen, and studied for sleep.
What it is
Glycine makes up about a third of the amino acids in collagen. It also acts as a calming signal in the nervous system.
Food sources
Gelatin and bone brothMeatFishLegumes
What the research shows
- Small human studies have looked at glycine before bed and subjective sleep quality.
- Larger, longer trials are needed.
Read the published research on PubMed →
Food first: most people get what they need from a varied diet with enough total protein. Talk to a provider or registered dietitian before adding a supplement, especially if you take medication or have a health condition.
Similar evidence level
Conditionally essential amino acid
Arginine
A precursor to nitric oxide, though oral supplements are poorly absorbed for that purpose.
Limited evidenceConditionally essential amino acidGlutamine
The most abundant amino acid in the blood, often oversold for muscle recovery.
Limited evidenceNonessential amino acidTyrosine
A building block for dopamine and norepinephrine, studied under acute stress.
Limited evidence