Glycine
Also called: aminoacetic acid, glycine hydrochloride, collagen amino acid.
The smallest of the amino acids, abundant in collagen, sold for sleep on the strength of three small Japanese trials at 3 g before bedtime.
What it is
Glycine is the smallest of the amino acids (75 g per mole). It serves as a building block for proteins, including collagen, and as a neurotransmitter, with excitatory and inhibitory roles depending on the receptor. The body makes it, but Examine notes data suggesting it may be conditionally essential. People buy it for sleep, and increasingly by way of collagen.
What the label does not say
- The sleep trials are few, small and run by researchers from an amino acid manufacturer: 3 g one hour before bedtime, with improved subjective sleep quality in people prone to insomnia (2006), shorter sleep latency on polysomnography (2007) and, in 7 men sleep-restricted for 3 nights, less fatigue the next day and better psychomotor vigilance (2012).
- The Canadian workout supplements monograph caps glycine at 1.8 g per day for the claim "source of amino acid". A bottle dosed according to that monograph does not reach the 3 g used in the sleep trials.
- Three grams is what about 200 g of roasted chicken breast (1.5 g per 100 g) or 16 g of powdered gelatin provides. Ten grams of gelatin already brings around 1.9 g: someone who takes collagen in the morning and glycine at night is stacking it without seeing it.
- The mechanism proposed by the same authors is a drop in core temperature at bedtime, not sedation: what is reported is perceived sleep quality, not forced sleep onset.
The forms on the shelf
- Powder: the format that allows the 3 g dose used in the trials. It tastes sweet, as the NIH toxicology database describes.
- Capsules and tablets: the trial dose is counted in grams, not milligrams; read the content per unit.
- Collagen and gelatin: provide it without saying so. Glycine, proline and hydroxyproline make up 57% of the amino acids in collagen, and powdered gelatin contains 19 g of glycine per 100 g according to the Canadian Nutrient File.
Published reference values
- No recommended intake or upper limit: a non-essential amino acid, made by the body. Sleep trial dose: 3 g, about one hour before bedtime, over a few nights.
- Health Canada, workout supplements monograph: 160 mg to 1.8 g per day for the claim "source of non-essential amino acid".
- Tolerance: Examine reports doses of up to 45 g per day with no apparent adverse effect, and 800 mg per kg per day for six weeks in schizophrenia trials, a dose described as impractical.
When
About one hour before bedtime in the trials. As a powder, it dissolves in water or herbal tea, and its sweet taste goes down without a sweetener.
To mention to a professional
- Kidney or liver disease, pregnancy and breastfeeding: little data at these doses, check with a health care professional.
What it is sold for, and what the data show
Glycine is sold as a natural, risk-free sleep aid. The risk-free part holds up: it is a dietary amino acid, tolerated at far higher doses. The sleep part rests on three small trials from the same industry group, never replicated at scale. Little risk, little evidence.
From the plate first
Powdered gelatin: 19 g per 100 g. Roasted chicken breast: 1.5 g per 100 g. Cooked ground beef: about 1.7 g per 100 g. Whole hard-boiled egg: 0.4 g per 100 g (Canadian Nutrient File).
Sources
- Examine.com, Glycine
- Bannai et al., The effects of glycine on subjective daytime performance in partially sleep-restricted healthy volunteers, Frontiers in Neurology, 2012
- Bannai and Kawai, New therapeutic strategy for amino acid medicine: glycine improves the quality of sleep, Journal of Pharmacological Sciences, 2012
- Roles of dietary glycine, proline, and hydroxyproline in collagen synthesis and animal growth, Amino Acids, 2018 (abstract on AGRIS, FAO)
- Health Canada, Canadian Nutrient File, 2015
- Health Canada, monograph, Workout Supplements
- NIH PubChem (HSDB), Glycine
Educational information, drawn from the sources above. It does not replace the advice of a health professional, who remains the reference for your situation, your medications, pregnancy or breastfeeding.