Glycine for sleep: a lesser-known amino acid, and its small studies
Glycine is one of the simplest amino acids, and it has quietly become a sleep supplement. The human research is thin and comes largely from one company. Here is what it found, read without the shine.
contentsA simple amino acid with a new job
Key points
- The human sleep studies on glycine used 3 grams taken before bed.
- One study reported better self-rated sleep and faster sleep onset on lab recordings.
- A second analysed just 7 men after three nights of shortened sleep, with mixed results.
- The second study was run largely by a company that makes glycine, using its own staff as volunteers.
- The proposed mechanism, a drop in body temperature, was not measured in that human study.
A simple amino acid with a new job
Glycine is the smallest amino acid. Your body makes it, and it is found in protein foods. In the last few years it has been rebranded as a sleep supplement, often sold in 3 gram servings.
That 3 gram figure comes straight from the research. So does almost everything else you will read about it, which is why the research deserves a close look.
The two studies people cite
table · the human glycine sleep studies
| Study | Who and how | What was reported |
|---|---|---|
| Yamadera et al., 2007[52] | Volunteers with ongoing unsatisfying sleep. 3 g before bed | Better self-rated sleep, faster sleep onset and deep sleep onset on lab recordings, less daytime sleepiness |
| Bannai et al., 2012[53] | 7 healthy men, sleep cut by 25% for three nights. 3 g or placebo before bed | Less fatigue and faster reaction time on day one. Sleepiness only a trend. No subjective difference by day three |
The 2007 paper reported its lab findings without changes to the overall structure of sleep.[52] We could not access its full results or sample size, so we have not quoted numbers we cannot check.
How small is small?
The 2012 study enrolled ten men and analysed seven. All were employees of the company that makes glycine, three of the five authors worked there, and only the participants, not the researchers, were blinded.[53]
Studies like this are a reasonable way to explore an idea. They are not a basis for confident claims, and the authors’ own results faded by the third night.
The body temperature idea
The popular explanation is that glycine helps the body shed heat, lowering core temperature in a way that eases sleep. That idea comes mainly from earlier animal work. In the 2012 human study, temperature was not measured.[53] It is a plausible theory, not a demonstrated mechanism.
Where it fits
Glycine sits in the same bracket as L-theanine: a handful of small, industry-linked studies with modest findings.[38] If sleep is poor enough to look for a supplement, it is poor enough to mention to a doctor, who may suggest a sleep diary or a sleep study.[3]
The sleep debt calculator is a useful reality check on how much sleep you are really losing each week.
Every supplement claim, traced to its study.
Our free list sends each new ingredient check, including who funded the research.
Sources
- Yamadera et al., 2007. Glycine ingestion improves subjective sleep quality in human volunteers, correlating with polysomnographic changes. Sleep and Biological Rhythms.
- Bannai et al., 2012. The effects of glycine on subjective daytime performance in partially sleep-restricted healthy volunteers. Frontiers in Neurology.
- Bulman et al., 2025. The effects of L-theanine consumption on sleep outcomes: a systematic review and meta-analysis. Sleep Medicine Reviews.
- NHLBI, 2022. Insomnia: Diagnosis. National Heart, Lung, and Blood Institute (NIH).
This article is educational and isn’t medical advice. It was written and checked by the UNWIRE™ editorial team; no clinician has reviewed it yet. UNWIRE™ is a nutrition company, and this article does not describe any product.
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