What it means
Glycine is the smallest amino acid and makes up about a third of collagen. It is a building block of glutathione, the cell's main antioxidant, which falls with age partly because glycine and cysteine run short. It also acts as an inhibitory neurotransmitter in the brainstem and lowers core body temperature slightly, which is the proposed mechanism for its effect on sleep.
Typical intake from food is 2–3 g per day; supplements provide 3–5 g, often taken before bed.
Why it matters for longevity
Glutathione decline is linked to oxidative damage, mitochondrial dysfunction and insulin resistance in older adults, and glycine is the cheaper of the two amino acids needed to rebuild it. Separately, glycine is one of the few supplements with a controlled sleep-quality result.
What the evidence says
In the ITP, glycine (8% of diet) extended lifespan in mice by about 4–6% in both sexes — small but significant. The GlyNAC trial (Kumar 2023, 24 older adults, glycine plus N-acetylcysteine for 16 weeks, placebo-controlled) restored glutathione, improved mitochondrial fuel oxidation, insulin resistance, gait speed, grip strength and several ageing markers; the effects faded after stopping. It was small but well designed.
For sleep, two Japanese trials (Inagawa 2006, Yamadera 2007) found 3 g before bed improved subjective sleep quality and reduced next-day fatigue; a 2012 study showed it reduced daytime sleepiness after sleep restriction. The effects are modest and the trials small.
How to measure or use it
- Glutathione and its precursors can be measured in red blood cells by specialist labs; routine panels do not include them.
- For sleep: 3 g 30–60 minutes before bed, judged on a wearable or a sleep diary over two weeks.
- For the GlyNAC effect: the trial used about 1.3 g/kg/day each of glycine and NAC — far above sleep doses — under supervision; the accessible endpoints are HOMA-IR and gait speed.
Related
- Supplements that have evidence — the ranking
- Sleep and longevity — where a sleep aid fits
- The sleep protocol — glycine inside a plan
Frequently asked questions
Does glycine help you sleep?
Small trials show 3 g before bed improves subjective sleep quality and reduces next-day fatigue. It is not a sedative.
What is GlyNAC?
Glycine plus N-acetylcysteine, dosed to restore glutathione. A 16-week placebo-controlled trial in older adults improved several ageing markers; effects reversed when stopped.
Can I get enough from collagen?
A 10–15 g collagen serving gives 3–4 g of glycine, equivalent to a sleep dose. Gelatin and bone broth are the food sources.
Want this applied to your own numbers?
Fifteen minutes of intake, your labs, a human-reviewed protocol within about 24 hours, three documents, a free coach call and check-ins through the cycle. €399, follow-up included.
Build my protocol Book a 15-minute call