Does Glycine Supplementation Actually Improve Sleep Quality?
Three grams of glycine taken within an hour of bedtime improved subjective sleep quality and shortened the polysomnographic latency to sleep onset in 11 volunteers who had been continuously experiencing unsatisfactory sleep. This was a randomized, single-blinded, placebo-controlled crossover trial, not a double-blind study, and it was small: eight women and three men aged 30 to 57, each serving as their own control. On the St Mary’s Hospital sleep questionnaire, glycine improved satisfaction with the night’s sleep (p = 0.046), reduced reported difficulty getting to sleep (p = 0.008), shortened reported time to fall asleep (p = 0.002), and raised subjective sleep efficacy, the ratio of sleep time to time in bed (p = 0.018). On polysomnography, glycine shortened the latency to sleep onset (p = 0.01) and the latency to slow wave sleep (p = 0.019), while sleep architecture, the proportion of the night spent in each stage, was unchanged.
Dr. Kumar’s Take
The design here is more modest than the way glycine is usually marketed, and I want to be straight about that. Eleven subjects, a single-blinded crossover, and two consecutive nights of recording per arm with the first night discarded as acclimatization. That is hypothesis-generating work, not a definitive trial.
What I do credit is the internal consistency. The subjective reports and the polysomnography point the same direction: people said they fell asleep faster, and the electroencephalogram showed they reached stage 2 sleep and slow wave sleep sooner. The proportions of each sleep stage did not shift, which is the part I find clinically interesting. Benzodiazepines reshape sleep architecture; here the architecture stayed intact and the night simply started earlier. The authors make that same distinction, arguing glycine works in a different way than traditional hypnotics.
The daytime findings are thinner and I would not lean on them. The Stanford Sleepiness Scale showed only a tendency in favor of glycine (p = 0.058). The visual analog scale showed a benefit at a single time point, 10:00 hours (p = 0.009), and the memory recognition task at 12:00 hours (p = 0.004). Single-timepoint effects in a study this size need replication before I would tell a patient to expect sharper afternoons.
Key Findings
The randomized, single-blinded, placebo-controlled crossover trial found that 3 grams of glycine taken within 1 hour before bedtime improved several sleep measures. Subjective ratings improved on satisfaction with the night’s sleep (p = 0.046), on difficulty getting to sleep (p = 0.008), and on how long it took to fall asleep (p = 0.002). Subjective sleep efficacy, sleep time divided by time in bed, also rose (p = 0.018).
Polysomnography showed a shorter latency to sleep onset, defined as the first appearance of stage 2 sleep (p = 0.01), and a shorter latency to slow wave sleep, the first appearance of stage 3 (p = 0.019). Latency to REM sleep did not change, and the ratios of each sleep stage across the whole sleep period were not altered. A representative hypnogram showed either more frequent deep sleep early in the night or less wake time after sleep onset following glycine.
For the day after, glycine showed a tendency to improve the total Stanford Sleepiness Scale score (p = 0.058). On the visual analog scale item “how sleepy are you?”, glycine reduced sleepiness at 10:00 hours (p = 0.009). On a memory recognition task, glycine ingestion the previous night improved the correct response ratio at 12:00 hours (p = 0.004). No serious adverse effects from glycine or placebo were observed during the study period.
Brief Summary
This randomized, single-blinded, placebo-controlled crossover trial examined glycine supplementation in 11 volunteers who had been continuously experiencing unsatisfactory sleep, with a mean Pittsburgh Sleep Quality Index score of 8.07 ± 1.34 and a range of 7 to 11. Participants took either 3 grams of granule glycine or a placebo matched for flavor within 1 hour before bedtime, with polysomnography recorded through the night, subjective sleep quality assessed the next morning by the St Mary’s Hospital sleep questionnaire, and daytime sleepiness and cognitive performance measured at set times through the following day and evening. The crossover design allowed each participant to serve as their own control.
Study Design
The study used a randomized, single-blinded, placebo-controlled crossover design with polysomnographic monitoring carried out in hospital. A set of examinations over two consecutive nights and days was repeated twice, with at least 1 week between them. All data from the first night were used for acclimatization to the protocol and were excluded from the results.
Electroencephalograms were recorded at C3, C4, O1 and O2, and sleep stages were scored by visual inspection using the Rechtschaffen and Kales criteria. Subjective sleep quality was assessed the next morning with the St Mary’s Hospital sleep questionnaire. Daytime sleepiness was measured with the Stanford Sleepiness Scale and a visual analog scale at 08:00, 10:00 and 12:00 hours, and again at 21:00 and 23:00 hours. Cognitive function was assessed with a memory recognition task in which a target stimulus and a test stimulus were presented 1500 ms apart and the subject responded if they matched.
Participants were told to keep their usual lifestyle and to avoid extra alcohol and supplements containing caffeine or vitamin B12. Women menstruating during the study period were excluded. Polysomnographic and subjective sleep data were analyzed with Wilcoxon’s signed rank test, and daytime data with two-way repeated measures ANOVA followed by Fisher’s least significant difference test, with significance set at p < 0.05.
Results You Can Use
Three grams of glycine taken within 1 hour before bedtime improved subjective sleep quality and shortened the time to fall asleep, both as reported by the participants and as recorded on polysomnography.
The polysomnographic benefit was specifically in latency: faster entry into stage 2 sleep and faster entry into slow wave sleep. The distribution of sleep stages across the night did not change, and REM latency did not change. Sleep efficacy improved on the subjective measure, the ratio of sleep time to time in bed.
Daytime effects were smaller. Sleepiness on the Stanford scale showed only a trend, with benefits on the visual analog scale at 10:00 hours and on memory recognition at 12:00 hours.
Why This Matters For Health And Performance
Most sleep supplements are sold on mechanism and testimonial. This trial put glycine in front of a polysomnograph and found that the subjective reports lined up with the recordings, which is a higher bar than most over the counter sleep products clear.
The pattern also matters clinically. Sleep architecture was preserved while sleep onset arrived sooner. The authors argue on that basis that glycine improves sleep quality in a different way than traditional hypnotic drugs such as benzodiazepines. In the trial itself, no serious adverse effects were observed with glycine or placebo, and the authors cite an earlier report that 9 grams of glycine, three times the dose used here, produced neither acute serious adverse events nor a daytime sleepiness carry over effect.
How to Apply These Findings in Daily Life
- Use the dose that was studied: 3 grams of glycine, which is the amount tested in this trial
- Time it the way the trial did: within 1 hour before bedtime
- Set the right expectation: the measured benefit was falling asleep sooner and rating the night more favorably, not a change in how the night was structured
- Choose quality supplements: look for pure glycine powder or capsules from a reputable manufacturer
- Combine with sleep hygiene: this trial asked participants to keep a regular lifestyle and avoid extra alcohol and caffeine, so treat glycine as an addition to those basics rather than a substitute
- Monitor your own response: track how long you take to fall asleep and how you feel the next day, since this trial ran in 11 people and individual responses may differ
Limitations To Keep In Mind
Eleven participants is a small sample, and the trial was single-blinded rather than double-blinded, so expectation effects on the self-reported measures cannot be excluded. Participants had been continuously experiencing unsatisfactory sleep by questionnaire, not a diagnosed sleep disorder, so these results do not tell you how glycine performs in clinical insomnia. Each arm involved two consecutive nights, with the first discarded for acclimatization, so this speaks to short-term use only. Several daytime results rested on single time points, and the Stanford Sleepiness Scale result did not reach significance.
Related Studies And Internal Links
- Glycine’s Sleep-Promoting Effects: NMDA Receptor Mechanisms
- Glycine Effects on Daytime Performance in Sleep-Restricted Volunteers
- Magnesium Supplementation Improves Sleep Quality in Elderly
- Melatonin for Sleep Disorders: Meta-Analysis Evidence
- How to Sleep Better: Science Daily Playbook
FAQs
How much glycine was used, and when was it taken?
Three grams of granule glycine, taken within 1 hour before bedtime. The placebo was a reduced form of malt sugar with the same flavor as glycine.
Did glycine change the structure of sleep?
No. The ratios of each sleep stage across the whole sleep period were unchanged, and latency to REM sleep was unchanged. What shortened was the time to reach stage 2 sleep (p = 0.01) and the time to reach slow wave sleep (p = 0.019).
Did glycine cause next-day sleepiness?
Not in this trial. Glycine showed a tendency to improve the Stanford Sleepiness Scale score (p = 0.058), reduced visual analog scale sleepiness at 10:00 hours (p = 0.009), and improved memory recognition performance at 12:00 hours (p = 0.004). The authors also cite a prior report that 9 grams produced no daytime sleepiness carry over effect.
Conclusion
In 11 volunteers with persistently unsatisfactory sleep, 3 grams of glycine within an hour of bedtime improved subjective sleep quality and subjective sleep efficacy, and shortened the polysomnographic latency to both sleep onset and slow wave sleep, without altering sleep architecture. The trial was randomized, single-blinded and small, so I read it as encouraging early evidence for a well tolerated amino acid rather than settled proof.
