Evidence supporting the use of: Tryptophan
For the body system: Parasympathetic Nervous System

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Synopsis

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

Tryptophan is an essential amino acid that serves as a biochemical precursor for serotonin, a neurotransmitter deeply involved in the regulation of mood, sleep, and certain autonomic functions. The parasympathetic nervous system (PNS) is responsible for "rest and digest" activities and is influenced by neurotransmitters, including serotonin. There is some scientific rationale for the use of tryptophan to support the PNS indirectly: by increasing serotonin levels, tryptophan may help modulate autonomic balance, favoring parasympathetic activity, particularly in the context of stress reduction and sleep enhancement.

Several studies have shown that supplementation with tryptophan can increase central serotonin synthesis, leading to enhanced mood and improved sleep, both of which are associated with increased parasympathetic tone. However, direct evidence linking tryptophan supplementation specifically to measurable improvements in PNS function is limited. Most research focuses on its effects on mood, anxiety, and sleep, rather than on direct autonomic biomarkers such as heart rate variability (HRV) or vagal tone. Thus, while there is some scientific support for the idea that tryptophan can influence the PNS via its role in serotonin synthesis, the evidence is indirect and moderate at best.

In summary, tryptophan has a scientifically plausible, though not robustly proven, role in supporting the parasympathetic nervous system, primarily through its effects on serotonin and related aspects of autonomic balance.

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