In 30 seconds
- Glycine is an amino acid that your body makes and that you also get from food, especially from collagen-rich foods.
- In Japanese studies, 3 g before bed improved perceived sleep quality, shortened the time taken to fall asleep and reduced sleepiness the next day.
- In animals, it appears to work by lowering core body temperature, one of the natural steps in falling asleep.
Glycine is one of the most interesting ingredients being studied for sleep, and also one of the least known. This is what has been researched. If you are after the practical answer, you will find it in glycine for sleep.
What glycine is
It is the simplest amino acid. Your body makes it, and you also get it from food, especially from foods rich in collagen and gelatine. It is part of proteins and also works as a messenger in the nervous system.
Level of evidence by outcome
| Outcome | Evidence | What the data show |
|---|---|---|
| Perceived sleep quality | Preliminary | Improvement in small studies with 3 g before bed. |
| Time taken to fall asleep | Preliminary | Shorter in one study with sleep recording. |
| Sleepiness and tiredness the next day | Preliminary | Less tiredness and faster reactions after short nights, in 7 people. |
The rating is our own, based on the number of studies, their quality and the consistency of the results.
The key studies
| Study | Type | Sample | Outcome |
|---|---|---|---|
| Yamadera et al., 2007 | Trial with sleep recording | Adults with poor sleep quality | 3 g before bed: better perceived sleep quality, they fell asleep sooner and reached deep sleep sooner. Less sleepiness and better memory the next day. 1 |
| Bannai et al., 2012 | Single-blind crossover trial | 7 healthy men with 25% less sleep | 3 g before bed: less tiredness on the first day and faster reactions in the vigilance test. 2 |
| Kawai et al., 2015 | Animal study | Rats | Glycine acts on the brain's central clock, widens the blood vessels in the skin and lowers core temperature, which makes sleep easier. 3 |
Glycine in people
The dose and timing used in the studies
What has been seen in people
In the Yamadera study, adults who slept poorly took 3 g of glycine before bed. They reported sleeping better, and sleep recording confirmed that they fell asleep sooner and reached deep sleep sooner, while the overall structure of their sleep stayed the same. The next day they were less sleepy and did better in a memory test 1.
In the Bannai study, 7 healthy men slept 25% less for three nights. With 3 g of glycine 30 minutes before bed, they felt less tired on the first day and reacted faster in a vigilance test 2.
How it works (rat studies)
Glycine and temperature: the path to sleep
How it is thought to work
To fall asleep, your core temperature has to drop slightly. In rats, glycine acts on the brain's central clock, widens the blood vessels in the skin so the body loses heat and lowers core temperature 3. The authors suggest that this is how it makes sleep easier, through a different pathway from sleeping pills 1.
What we still need to find out
Frequently asked questions
What is glycine?
The simplest amino acid. Your body makes it and you also get it from food, especially from foods rich in collagen and gelatine. It is part of proteins and also works as a messenger in the nervous system.
How much glycine is taken for sleep in the studies?
The dose studied is 3 g, taken shortly before bed; in one of the studies, 30 minutes before.
Does glycine make you drowsy the next day?
The studies saw no next-day drowsiness: on the contrary, participants felt less sleepy and less tired during the day.
How does glycine work for sleep?
Through a natural pathway: in animals, glycine lowers core body temperature, one of the steps your body takes to fall asleep.
Sources
- Yamadera W, Inagawa K, Chiba S, Bannai M, Takahashi M, Nakayama K. Glycine ingestion improves subjective sleep quality in human volunteers, correlating with polysomnographic changes. Sleep Biol Rhythms. 2007;5(2):126-131. View publication
- Bannai M, Kawai N, Ono K, Nakahara K, Murakami N. The effects of glycine on subjective daytime performance in partially sleep-restricted healthy volunteers. Front Neurol. 2012;3:61. View publication
- Kawai N, Sakai N, Okuro M, et al. The sleep-promoting and hypothermic effects of glycine are mediated by NMDA receptors in the suprachiasmatic nucleus. Neuropsychopharmacology. 2015;40(6):1405-1416. View publication
Information based on published studies. It does not replace the advice of a doctor or registered dietitian. The results describe what was measured in each study, not the properties of any specific product. A varied and balanced diet and a healthy lifestyle are important.
