Evidence supporting the use of: L-glycine
For the body system: Parasympathetic Nervous System

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Synopsis

Source of validity: Scientific
Rating (out of 5): 2

L-glycine is a non-essential amino acid that functions as an inhibitory neurotransmitter in the central nervous system, including regions involved in parasympathetic activity. There is some scientific evidence that glycine can promote relaxation and support autonomic balance. Glycine binds to specific glycine receptors in the brain and spinal cord, leading to inhibitory effects that may help modulate stress responses and promote a state of calmness. Some studies have suggested that glycine supplementation can improve sleep quality, reduce core body temperature, and decrease subjective feelings of fatigue, which may indirectly support parasympathetic (rest-and-digest) functions.

However, while these effects are promising, direct evidence linking glycine supplementation specifically to enhanced parasympathetic nervous system activity in humans is limited. Most research focuses on its role in sleep and general nervous system inhibition rather than direct modulation of parasympathetic tone. Animal studies and in vitro experiments provide some mechanistic support, but robust clinical trials are lacking.

In summary, there is preliminary scientific evidence suggesting that L-glycine may support relaxation and sleep, which are associated with parasympathetic activity. However, the evidence base for its direct support of the parasympathetic nervous system is modest, meriting a rating of 2 out of 5.

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