Most sleep supplements share one problem: they are advertised but never measured. Glycine is different. Here, people slept in a laboratory with electrodes on their heads, and the researchers recorded what happened during the night.
What polysomnography showed
In 2007, a Japanese research group led by Wataru Yamadera published a study in Sleep and Biological Rhythms. Participants with unsatisfactory sleep took 3 grams of glycine before going to bed. Sleep was not measured with questionnaires but with polysomnography: brain waves, eye movements, muscle tension. This is how sleep medicine measures when it wants to know for sure.
What came out of it:
- The time until falling asleep became measurably shorter.
- The way into deep sleep became shorter too.
- Sleep efficiency rose: more actual sleep per hour in bed.
- The day after: less sleepiness, better performance in a memory test.
The most elegant finding is in the detail: sleep architecture stayed the same. Classic sleeping pills shift the shares of the sleep stages. You sleep longer, but differently. Glycine did not do that. It shortened the way into sleep and left sleep itself as it was.
The test closest to everyday life
Do you notice anything after too little sleep? Bannai and colleagues looked at this in 2012 in Frontiers in Neurology.
The set-up was deliberately uncomfortable: sleep time was cut by a quarter for three nights in a row, a situation many people know from a hard week. Before bed, participants got 3 grams of glycine or a placebo.
The next day, the glycine group showed:
- Significantly less tiredness
- A tendency towards less sleepiness
- Measurably better reaction performance in the psychomotor vigilance test, on the first and on the third day
For everyday life, this is the most interesting finding. The nights were short, and with glycine the day after was still easier for the participants.
Why temperature might be the explanation
The most plausible explanation has nothing to do with sedation. It has to do with heat.
The trail leads through blood flow. In animal studies, glycine widened the blood vessels in the hands and feet. That is where the body releases heat, and the core temperature drops faster. Kawai and colleagues showed this in rats in 2015, with a dose that, converted to body weight, would be several times the 3 grams.
That very drop is the starting signal for falling asleep. The body does it every night on its own. That glycine speeds it up is the hypothesis behind the sleep studies. According to the animal studies, receptors in the suprachiasmatic nucleus are involved, in the very brain region that runs the internal clock.
Our article on sleep temperature tells the other half of the story: a bed that is too warm slows down the same signal.
What you should know about the studies
The studies do not rely on questionnaires alone. They measured with polysomnography and a reaction test, methods that cannot be talked up. For a supplement sold over the counter, that is a lot: most products on the sleep shelf have no such measurement at all.
Context matters too: the groups were small, and eleven people took part in the laboratory study. Most of the studies come from one research group that included an amino acid manufacturer. The next step would be a larger, independent repeat.
Does more help more?
All three sleep studies used 3 grams of glycine, about an hour before bed. All the results above come from that amount, so that is what we stick to. The stated recommended daily dose must not be exceeded.
On paper, the body is short of about 10 grams of glycine a day; the calculation is in our introductory article. But that gap concerns the whole body, mostly the building of collagen. For sleep, what counts is the amount from the laboratory.
How an evening with glycine goes, from taking it to the next morning, is described in a separate article.
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 and Biological Rhythms, 2007, Volume 5, pages 126–131. To the study
- Bannai M, Kawai N, Ono K, Nakahara K, Murakami N: The effects of glycine on subjective daytime performance in partially sleep-restricted healthy volunteers. Frontiers in Neurology, 2012. To the study
- Inagawa K et al.: Subjective effects of glycine ingestion before bedtime on sleep quality. Sleep and Biological Rhythms, 2006. To the study
- Kawai N, Sakai N, Okuro M, Karakawa S, Tsuneyoshi Y, Kawasaki N, Takeda T, Bannai M, Nishino S: The sleep-promoting and hypothermic effects of glycine are mediated by NMDA receptors in the suprachiasmatic nucleus. Neuropsychopharmacology, 2015. To the study
- Meléndez-Hevia E, De Paz-Lugo P, Cornish-Bowden A, Cárdenas ML: A weak link in metabolism: the metabolic capacity for glycine biosynthesis does not satisfy the need for collagen synthesis. Journal of Biosciences, 2009, Volume 34, Issue 6, pages 853–872. To the study
