Polygala, particularly Polygala tenuifolia (commonly known as Yuan Zhi or Chinese Senega), has a long history of use in Traditional Chinese Medicine (TCM) where it is believed to calm the spirit, enhance cognitive function, and support emotional balance. Within TCM frameworks, it is sometimes referenced for its ability to "nourish the heart and quiet the spirit," indirectly suggesting support for the parasympathetic nervous system, which governs rest, relaxation, and recovery functions in the body.

However, while Polygala tenuifolia has been studied for neuroprotective, anxiolytic, and antidepressant effects in animal models, the direct impact on the human parasympathetic nervous system has not been robustly demonstrated in scientific literature. Most available research focuses on its effects on neurotransmitters like acetylcholine and on neuroinflammation, rather than specific modulation of parasympathetic activity.

In summary, the use of Polygala to support the parasympathetic nervous system is primarily justified by traditional usage and interpretations from TCM, with modest supporting evidence from preclinical studies suggesting neurological benefits. There is currently insufficient high-quality clinical evidence directly linking Polygala supplementation to measurable improvements in parasympathetic nervous system function in humans.