Not medical advice. I am a software engineer, not a physician. This page documents my own protocol and the research I read while building it. Talk to a qualified clinician before changing your supplementation, diet or any treatment. Lab reference ranges quoted here vary by laboratory and by individual.
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Glycine is the simplest amino acid, with just a hydrogen atom as its side chain. Despite its structural simplicity, it plays outsized roles in human physiology. It constitutes approximately 33% of all amino acids in collagen — the most abundant protein in the body — making it essential for skin, joints, tendons, and bone matrix integrity. Beyond structural support, glycine functions as an inhibitory neurotransmitter in the brainstem and spinal cord, serves as a precursor to glutathione (the body's master antioxidant), and participates in creatine and heme synthesis. Modern diets that avoid animal connective tissue are chronically low in glycine, creating a functional deficit that supplementation can correct.
Glycine improves sleep quality through a unique thermoregulatory mechanism. When ingested before bed, it acts on NMDA receptors in the suprachiasmatic nucleus (the body's master clock), triggering peripheral vasodilation that lowers core body temperature. This drop in core temperature is one of the strongest physiological signals for sleep onset. Unlike sedative sleep aids, glycine enhances sleep quality without causing next-day grogginess or altering sleep architecture — REM and deep sleep stages remain intact.
As a glutathione precursor, glycine combines with cysteine and glutamate to form glutathione (GSH), the tripeptide that neutralizes reactive oxygen species in every cell. Research shows that glycine availability is often the rate-limiting factor for glutathione synthesis in older adults, making supplementation particularly valuable for maintaining antioxidant defenses with age.
In collagen synthesis, glycine occupies every third position in the collagen triple helix (Gly-X-Y repeating sequence). Without adequate glycine, the body cannot produce collagen at optimal rates, leading to slower wound healing, thinner skin, and weaker connective tissues. Supplementing glycine alongside vitamin C and lysine provides the complete substrate for collagen production.
Brand: NOW Foods — Glycine, 1,000 mg (100 Veg Capsules)
| Time | Dose | Notes |
|---|---|---|
| 4:30 AM (fasted) | 3 g (3 capsules) | Fasted morning dose for glutathione and collagen support |
Total daily dose: 3 g. Glycine has a sweet taste and excellent tolerability even at higher doses (up to 9 g/day in studies). See the full timing context in the Supplement Stack.
Bannai et al. (2012) conducted a randomized, single-blind, crossover study showing that 3 g of glycine before bedtime significantly improved subjective sleep quality, reduced sleep onset latency, and improved next-day cognitive performance including reaction time and memory tasks. Participants reported feeling more refreshed upon waking without any sedative hangover. PMID: 22293292
De Paz-Lugo et al. (2018) demonstrated that glycine supplementation enhances collagen synthesis in human chondrocytes and is essential for maintaining cartilage extracellular matrix. The study confirmed that glycine availability is a limiting factor for collagen production and that supplementation at physiological concentrations significantly increases type II collagen output. PMID: 28853725
Jackson et al. (2004) found that glycine administration in healthy human subjects increased plasma glutathione levels and enhanced the overall antioxidant capacity. The study demonstrated that glycine supplementation supports the glutathione synthesis pathway, particularly when cysteine availability is adequate (as ensured by concurrent NAC supplementation). PMID: 11833323
NOW Foods — Glycine, 1,000 mg (100 Veg Capsules)
Price: $11.77
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A 2025 clinical trial published in npj Aging found that oral supplementation with a collagen amino acid composition (3:1:1 glycine:proline:hydroxyproline ratio) reduced biological age by 1.4 years within 6 months. In mice, the same supplementation improved grip strength and prevented age-related fat accumulation. Cell culture studies showed that increasing glycine concentration boosted type II collagen synthesis by 60–75%, with effects persisting even at higher levels — unlike other amino acids. For sleep, a systematic review of 50 human studies confirmed that 3 g of glycine taken before bedtime improves sleep quality, reduces nighttime awakenings, and enhances next-day alertness and cognition. The mechanism involves glycine-mediated peripheral vasodilation that triggers body temperature reduction, aligning with the circadian sleep signal. Based on the totality of evidence, 3 g nightly appears safe with no significant adverse effects reported.