Glycine is a non-essential amino acid in human nutrition. This means that the cells of the body are able to synthesise glycine from other amino acids and in this regard there is no requirement to provide a dietary source. The cells of the body synthesise glycine for a number of purposes, and one of these is as a neurotransmitter in the brain and other tissues. In this role as a neurotransmitter, glycine has a general inhibitory effect on neuronal circuits, and this suggests that like other inhibitory neurotransmitters like GABA, that it has an overall calming effect. However, glycine also partially agonises the N-methyl-D-aspartate ion channel, and this channel is known to have significant excitatory properties. Therefore as with all neurochemistry, the exact role for glycine is not fully understood and it is unclear how it affects behaviour and mood. However, one effect that has been reasonably well reported relates to the inhibitory effects of glycine and this includes the ability of glycine to improve the quality of the sleep.
For example, ingestion of glycine is associated with a reduction in core body temperature, something that is known to occur and be necessary to maintain high quality sleep. Rats that consume glycine experience increased glycine content to their blood in combination with a decrease in core body temperature and an increase in cutaneous blood flow. In humans, glycine can improve subjective sleep quality in subjects experiencing poor quality sleep. In one study the quality of the sleep as determined by the sleep time and the amount of drowsiness in the day was improved with consumption of 3 grams of glycine before bed. In another study performed on healthy volunteers that were experiencing poor quality sleep, glycine significantly improved “fatigue”, “liveliness and peppiness”, and “clear-headedness”. Therefore human studies support the animal data in that glycine may be an effective sleep aid, and although the mechanism of action is not known, it may relate to reductions in core body temperature.
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