Glycine

Glycine is the smallest amino acid and an inhibitory neurotransmitter in the brain. Supplementation (3g pre-bed) has direct evidence for improving sleep quality, reducing subjective fatigue, and lowering core body temperature for better deep sleep. It also serves as a collagen building block.

Glycine is technically non-essential — the body can synthesize it from serine — but endogenous production often falls short of demand, particularly in adults consuming modern muscle-meat-dominant diets (which are higher in methionine than traditional nose-to-tail eating patterns that included glycine-rich connective tissue).

Glycine has multiple biological roles. It is a major inhibitory neurotransmitter in the brainstem and spinal cord (similar but distinct from GABA). It is a building block of collagen and glutathione. It serves as a methyl donor in the one-carbon cycle. It modulates NMDA receptors in the brain as a co-agonist. This last role underlies some of its sleep effects — glycine at the NMDA receptor triggers peripheral vasodilation and a measurable drop in core body temperature, which is one of the strongest physiological signals to initiate deep sleep.

The sleep evidence is notable. A series of trials by Bannai et al. showed that 3g of glycine 60 minutes before bed reduces sleep onset latency, improves subjective sleep quality, increases the time spent in slow-wave sleep, and reduces next-day fatigue. The effect size is modest but consistent, and the side effect profile is essentially nil. Glycine has become a common evening supplement alongside magnesium glycinate.

For women, glycine supports collagen synthesis (particularly relevant in the perimenopausal skin collagen decline), helps counterbalance the methionine-heavy amino acid profile of most animal protein sources (relevant to methylation cycle balance), and supports the deep sleep that typically declines during the hormonal transition. Practical dosing is 3g in water 30–60 minutes before bed.

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