Most sleep supplements have a problem: they are advertised, but never measured. With glycine it is different. Here there are investigations in which people slept in a laboratory with electrodes on their heads — and that makes the matter considerably more interesting.
What the polysomnography showed
In 2007, a Japanese research group led by Wataru Yamadera published an investigation in Sleep and Biological Rhythms. Participants with unsatisfactory sleep took 3 grams of glycine before going to bed. Measurement was not by questionnaire but by polysomnography — brainwave traces, eye movements, muscle tension. The gold standard of sleep research.
What came out of it:
- The time until falling asleep shortened measurably.
- The route into deep sleep also became shorter.
- 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, though, lies in the detail: the sleep architecture remained unchanged. Classic sleeping pills shift the proportions between the sleep stages — you sleep longer, but differently. Glycine did not do that. It shortened the route into sleep without rebuilding the sleep itself.
The test that comes closest to everyday life
Nicer than any laboratory curve is the question: do you notice anything when you have slept too little? That is exactly what Bannai and colleagues investigated in 2012 in Frontiers in Neurology.
The set-up was deliberately uncomfortable: sleeping time was cut by a quarter on three consecutive nights — that is, the situation most people know from a demanding week. Before going to bed there were 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 day as well as on the third
That is the finding of the whole series that comes closest to practice. Not necessarily “you sleep better”, but rather: with too little sleep, the following day is still noticeably less hard going.
Why temperature of all things could be the explanation
This is where it gets really interesting. The most plausible explanation has nothing to do with sedation, but with warmth.
The trail leads via blood flow. In animal experiments, glycine widened the blood vessels at the extremities: that is where heat is released, and the core temperature falls faster. Kawai and colleagues showed this in rats in 2015 — with a dose that, converted to body weight, would be a multiple of the 3 grams. In humans, core temperature under glycine has not been measured so far.
This very drop is the physiological start signal for falling asleep. The body does it by itself every night; whether glycine gives it a bit of speed is the hypothesis behind the sleep studies. The animal work suggests that receptors in the suprachiasmatic nucleus are involved — that is, in the very brain region that controls the body clock.
If you want to follow that up, our article on sleep temperature has the other half of the story: why a bed that is too warm slows down the same signal.
What you should know about the studies
The investigations so far provide informative insights into the effect of glycine. What is particularly interesting is that not only subjective assessments were looked at, but objective measurement methods such as polysomnography and psychomotor vigilance tests were used as well. This makes it possible to capture potential changes in sleep and recovery far more concretely.
Two things belong to the picture, however. The investigations are small — eleven people took part in the polysomnography study. At the same time, their detailed measurement methods deliver interesting and concrete insights into the effect of glycine. In addition, the studies come predominantly from one working group in which an amino acid manufacturer was involved.
That does not make the measurements any worse: polysomnography cannot be talked up, and neither can a psychomotor vigilance test. It only means that an independent repetition on a larger scale is still outstanding. For a freely available supplement, the evidence base is nonetheless above average — most have none at all.
The dose in question
In the sleep investigations mentioned, it was 3 grams of glycine about an hour before going to bed. At first that sounds like little — especially when you consider the amounts of glycine the body forms itself and takes in through food every day.
The body can make glycine itself, but there are indications that this own production together with the usual intake through food does not cover the entire requirement. A widely cited analysis by Meléndez-Hevia et al. from 2009 examined precisely this glycine balance: for a 70 kg adult, the authors estimated the body's own synthesis at about 3 grams per day and intake through food at a further 1.5–3 grams. Against this they set a considerably higher requirement for the various metabolic processes and calculated from it a possible daily supply gap of around 10 grams.
This is exactly where additional intake becomes interesting: the 3 grams from the sleep studies are not a “maximum dose”, but an amount specifically investigated for intake before going to bed. Other studies have also looked at higher amounts.
Where else glycine comes from and why the body budgets it chronically tightly is set out in our introductory 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
