Loranthus, particularly Loranthus parasiticus (also known as "Sang Ji Sheng" in Traditional Chinese Medicine, TCM), has a long history of use in traditional herbal practices, especially in East Asia. In TCM, it is classified as an herb that "tonifies the Liver and Kidneys," "strengthens sinews and bones," and is often claimed to "calm the fetus" during pregnancy. Its use in supporting the Spleen body system is less direct but emerges from its general categorization as a tonic and its inclusion in formulas addressing "Spleen deficiency" syndromes, which are thought to manifest as fatigue, muscle weakness, or poor digestion.

However, the traditional rationale does not map cleanly onto modern biomedical concepts. The "Spleen" in TCM theory involves broader digestive and metabolic functions rather than the anatomical spleen. Scientific studies on Loranthus primarily focus on its anti-inflammatory, antioxidant, and immunomodulatory properties, but robust clinical trials specifically validating its effects on the Spleen, as defined either by TCM or Western medicine, are lacking.

In summary, the use of Loranthus to support the Spleen is justified mainly by traditional usage and theory, with limited direct scientific evidence specific to this body system. The evidence is therefore rated as moderate for traditional use but weak from a scientific validation perspective.