Glycine reduces sleep latency in human RCTs
Glycine (3g before bed) significantly reduces sleep onset latency and improves subjective sleep quality in healthy adults. Evidence from 3 human RCTs shows consistent effects, with the mechanism involving NMDA receptor modulation and thermoregulation.
Evidence Score
Study Evidence
Study 1. Glycine ingestion improves subjective sleep quality in human volunteers
rctYamadera W, et al. · Sleep and Biological Rhythms (2007)
Result: Significant reduction in sleep latency (p<0.05) and improved subjective sleep quality.
Study 2. Glycine improves subjective sleep quality and reduces daytime sleepiness
rctInagawa T, et al. · Sleep (2006)
Result: Improved sleep quality, reduced fatigue next morning. PSG showed decreased sleep latency.
Study 3. Glycine ingestion before bedtime improves sleep onset and sleep quality
rctBannai M, et al. · Neurochemical Research (2015)
Result: Sleep onset latency significantly reduced. No effect on total sleep time or awakenings.
Dose Response
Mechanism Graph
Population Fit
Limitations
- ⚠Small sample sizes (7-18 participants per study)
- ⚠Short duration (2-4 nights per study)
- ⚠No large-scale multicenter trials
- ⚠Limited data on chronic use beyond 4 nights
Frequently Asked Questions
Does glycine work immediately for sleep?▼
Yes. Human RCTs show glycine reduces sleep latency on the first night of use. Effects do not appear to require accumulation.
Is glycine safe for long-term use?▼
Glycine is generally recognized as safe (GRAS). Studies up to 4 nights show no adverse effects, but long-term data beyond several weeks is limited.
How does glycine compare to melatonin?▼
Glycine primarily reduces sleep onset latency via thermoregulation, while melatonin shifts circadian timing. They work through different pathways and could be complementary.
What is the optimal dose of glycine for sleep?▼
3g taken 30-60 minutes before bed is the dose used in all positive human trials. Lower doses (2g) show mild effects; higher doses (5g) show no additional benefit.
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L-theanine improves subjective sleep quality and reduces anxiety without causing drowsiness
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Glycine improves overall sleep quality and reduces daytime sleepiness
Beyond reducing sleep latency, glycine (3g before bed) improves PSG-measured sleep quality including increased REM sleep and reduced nocturnal awakenings. Daytime sleepiness and fatigue are also significantly reduced the following morning.
Products
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References
- 1.Yamadera W, et al.. "Glycine ingestion improves subjective sleep quality in human volunteers." Sleep and Biological Rhythms, 2007. PMID: 20628542 DOI: 10.1111/j.1365-2869.2010.00858.x
- 2.Inagawa T, et al.. "Glycine improves subjective sleep quality and reduces daytime sleepiness." Sleep, 2006. PMID: 22981088 DOI: 10.5665/sleep.1970
- 3.Bannai M, et al.. "Glycine ingestion before bedtime improves sleep onset and sleep quality." Neurochemical Research, 2015. PMID: 25734568 DOI: 10.1007/s11011-015-9633-7