Glycine

Glycine is the simplest amino acid. Your body uses it as a building block for collagen, as one of three amino acids in glutathione (your main intracellular antioxidant) and as an inhibitory neurotransmitter in the brainstem.^[1] It is classed as non-essential because your body can make some of it. Under real-world demand, that synthesis falls short.

If you have heard glycine mentioned for sleep, skin or recovery, this page covers where it comes from, how much you need and what the research shows.

Sources of glycine

Your body makes glycine from serine, choline and threonine. The conversion is slow. A 2023 review in Ageing Research Reviews estimated that endogenous synthesis covers only a fraction of the daily need once collagen turnover, glutathione production and other demands are added together.^[1]

Free-form glycine is the pure amino acid as a white crystalline powder. Your gut absorbs it quickly. It carries a faintly sweet taste. This is the form used in most clinical sleep trials and in nōuxx Green Glow.

Collagen and gelatin are roughly one third glycine by weight. Hydrolysed collagen peptides also deliver proline and hydroxyproline. They are the main dietary route to high glycine intake for most women.^[4]

Bone broth is a traditional source. Glycine content varies widely with cooking time, bone type and dilution. A typical home-made batch delivers between 1 and 3 g per cup.

Muscle meat, fish and eggs contain modest amounts. Plant foods are low.

How much you need

There is no official recommended intake for glycine in the EU or in the United States. Average Western diets supply around 1.5 to 3 g of glycine per day from food. Estimated daily turnover for collagen synthesis alone runs higher than that.^[1]

Clinical research uses a wider range. Sleep trials typically test 3 g taken before bed. Skin and joint research tends to use collagen peptides at 5 to 15 g per day, which delivers roughly 2 to 5 g of glycine. Studies on glutathione status have used higher short-course doses.^[1]

The science on women's health

Sleep quality

Glycine has a small but consistent RCT base for sleep. Most trials are small. A 2023 randomised crossover study in Medicine and Science in Sports and Exercise tested a nightly blend containing glycine, tryptophan, magnesium, tart cherry and L-theanine in 16 healthy adults. Sleep onset latency dropped by 24 minutes. Total sleep time rose by 22 minutes. Sleep efficiency improved. The blend design means the effect cannot be pinned to glycine alone.^[2]

A 2024 trial in European Journal of Nutrition gave 15 g of glycine-rich collagen peptides one hour before bed for seven nights. Polysomnography showed fewer awakenings versus placebo. The study ran in 13 physically active men, so the result does not transfer cleanly to women.^[3]

The proposed mechanism is body temperature. Glycine at bedtime appears to lower core temperature through peripheral vasodilation, which speeds the natural drop that signals sleep onset.^[1] Honest read: the signal is real but the trials are short. Larger studies in women are still missing.

Skin and collagen synthesis

Glycine sits at every third position along the collagen triple helix. Without enough glycine in circulation, collagen synthesis cannot keep up with turnover.^[4] A 2024 review in Marine Drugs pulled together the trial data on collagen peptides for skin elasticity, hydration and wrinkle depth. Results are positive across most studies, with the strongest signal in women over 35 where collagen turnover slows.^[4]

Glycine is also one of three amino acids in glutathione. Glutathione is your main intracellular antioxidant. It protects skin cells from oxidative damage. When glycine supply runs low, glutathione synthesis stalls.^[5] This is the second pathway by which glycine supports skin during the follicular phase.

EU authorised health claims

Under EU law, no specific health claim is currently authorised for glycine. Glycine has not been through the EFSA dossier process that other ingredients have completed. Under EU food law, nōuxx cannot make a direct sleep, skin or antioxidant claim attached to glycine on pack or in marketing copy.

Research suggests glycine taken before bed may improve subjective sleep quality.^[2][3] The trials are small and several are not in women specifically. Until larger trials in women confirm an effect at typical supplemental doses, we do not make formal health claims for glycine.

References

[1] Johnson AA, Cuellar TL. Glycine and aging: evidence and mechanisms. Ageing Research Reviews 2023;87:101922. doi.org/10.1016/j.arr.2023.101922

[2] Langan-Evans C, Hearris MA, Gallagher C, et al. Nutritional modulation of sleep latency, duration, and efficiency: a randomized, repeated-measures, double-blind deception study. Medicine and Science in Sports and Exercise 2023;55(2):289-300. doi.org/10.1249/MSS.0000000000003040

[3] Thomas C, Kingshott RN, Allott KM, et al. Collagen peptide supplementation before bedtime reduces sleep fragmentation and improves cognitive function in physically active males with sleep complaints. European Journal of Nutrition 2024;63(1):323-335. doi.org/10.1007/s00394-023-03267-w

[4] Rahman A, Rehmani R, Pirvu DG, et al. Unlocking the therapeutic potential of marine collagen: a scientific exploration for delaying skin aging. Marine Drugs 2024;22(4):159. doi.org/10.3390/md22040159

[5] Rochette L, Dogon G, Rigal E, et al. Lipid peroxidation and iron metabolism: two corner stones in the homeostasis control of ferroptosis. International Journal of Molecular Sciences 2022;24(1):449. doi.org/10.3390/ijms24010449