Shan Yao also known as Chinese Yam, Nagaimo, Cinnamon Vine, or Rhizoma Dioscoreae is the rhizome of Dioscorea polystachya, which is a perennial climbing vine belonging to the family Dioscoreaceae. It can be used as a food and dietary supplement with a medicinal history of more than 2,000 years.
Dioscorea polystachya is a short-day crop and likes a warm environment. It often grows on hillsides, valley forests, bushes or weeds on roadsides at 150-1,500 meters above sea level. It native to East Asia and was introduced to the Americas and Europe as an ornamental crop and food crop in the 19th century. It is now widely cultivated in some countries in Asia.
Generally, the Chinese Yam is known as Huai Shan or Huai Shan Yao, which is produced in Huai Qing Fu (Jiaozuo), Henan Province. It is defined by the Chinese as Si Da Huai Yao (four famous medicines from Huaiqing), and the other three are Sheng Di Huang (Radix Rehmanniae), Niu Xi (Radix Achyranthis Bidentatae), and Ju Hua (Flos Chrysanthemi).
The most famous Huai Shan is the Tie Gun Shan Yao (Iron Rod Shan Yao) with traces of rust on the surface. It has high medicinal value and rich nutrition, and many ancient books have records about it.
After the first frost of each year, people gather the rhizomes of Dioscorea polystachya, remove their crude skin and fibrous roots, cut them into thick pieces, dry them, or moisten them thoroughly, stir-fry them with bran, and make them into Chinese herbs.
Shan Yao contains a variety of amino acids, such as serine, arginine, phenylalanine, tyrosine, glutamic acid, arginine, and aspartic acid. In addition, it also contains diosgenin, choline, polyphenol oxidase, glycoprotein, palmitic acid, oleic acid, azelaic acid, β-sitosterol, β-daucosterol, uracil, starch, polysaccharides, allantoin, fatty acids, vitamin C and a variety of trace elements.
According to , the medicinal property of Shan Yao is relatively mild, with a sweet taste. It has a certain therapeutic effect on the pathological changes of the spleen, lung, and kidney meridians.
In Chinese medicine, Shan Yao is often used to invigorate the spleen and nourish the stomach, promote fluid production and benefit lung, nourish kidney and arrest seminal emission, treat the loss of appetite and lassitude caused by the asthenia of splenic qi, weak waist and knee, dizziness, hot flashes, night sweats, leukorrheal diseases, frequent urination, chronic gastritis, chronic enteritis, dyspepsia, ulcerative stomatitis, eczema, diabetes, and chronic nephritis.
There are more than 300 kinds of traditional Chinese medicine prescriptions containing Shan Yao, such as Ren Shen Jian Pi Wan, Liu Wei Di Huang Wan，Zhi Bai Di Huang Wan, and Ren Shen Jian Pi Wan.
Health benefits of Shan Yao (Chinese Yam or Rhizoma Dioscoreae)
- Anti-oxidation, scavenging DPPH radical, hydroxyl radical, and superoxide anion, delaying aging.
- Inhibiting the proliferation of colon cancer cells HCT-116, human liver cancer SMMC-7721, Hepa1-6 cells, and melanoma.
- Reducing the damage of CCL4 to liver tissue and protecting the liver.
- Lowering blood sugar and blood lipids, antagonizing the increase in blood sugar caused by alloxan, epinephrine, or glucose.
- Promoting the regeneration, repair, and reconstruction of renal tubular cells and preventing renal ischemia-reperfusion injury.
- Enhancing the phagocytic ability of phagocytes, promoting the proliferation of lymphocytes and the production of antibodies, and improving immunity.
- Inhibiting gastric emptying and intestinal propulsion, relieving gastrointestinal smooth muscle spasm, and promoting digestion.
- Invigorating the spleen and benefiting qi, treating emaciation, lassitude, loss of appetite, and loose stool caused by the asthenia of splenic qi.
- Draining dampness and treating abnormal leucorrhea caused by the downward flow of damp turbidity.
- Benefiting the lung, nourishing lung yin and lung qi, alleviating cough and asthma caused by lung deficiency.
- Supplementing kidney qi and treating lumbar and knee weakness, frequent nocturnal urination, enuresis, spermatorrhea, and premature ejaculation caused by kidney qi deficiency.
- Nourishing kidney yin, treating seminal emission and thin leucorrhea caused by kidney yin deficiency.
- Invigorating qi and nourishing yin, treating hyperglycemia, urine sugar, polyuria, and polydipsia caused by a deficiency of both qi and yin.
Shan Yao is used with other Chinese herbs
- It with Bai Bian Dou (White Hyacinth Bean), Bai Zhu (Rhizoma Atractylodis Macrocephalae), and Ji Nei Jin (Endothelium Corneum Gigeriae Galli) can treat indigestion in children.
- It with Huang Qi (Astragalus Root), Tian Hua Fen (Radix Trichosanthis), and Zhi Mu (Rhizoma Anemarrhenae) can treat hyperglycemia, urine sugar, polyuria and polydipsia caused by a deficiency of both qi and yin.
- It with Tai Zi Shen (Radix Pseudostellariae) and Nan Sha Shen (Radix Adenophorae) can nourish lung yin and lung qi, alleviate cough and asthma caused by lung deficiency.
- It with Yi Zhi Ren (Sharpleaf Galangal Fruit) and Wu Yao (Radix Linderae) can treat nocturnal urination and enuresis caused by kidney qi deficiency.
- It with Shan Zhu Yu (Fructus Corni), Tu Si Zi (Semen Cuscutae), and Jin Ying Zi (Fructus Rosae Laevigatae) can treat thin leucorrhea caused by kidney qi deficiency.
Side effects of Shan Yao
Shan Yao is an edible vegetable with almost no side effects.
The fresh Shan Yao can easily cause skin irritation. If you feel itchy after peeling the skin of Shan Yao, it is recommended to clean the affected area and apply edible oil.
Precautions of Shan Yao
- The dosage of Shan Yao should be controlled at 15-30g.
- The dosage should not exceed 250g when consuming fresh Shan Yao.
- It can be made into decoction, pill, or mashed for external use.
- The unprocessed Shan Yao is recommended for nourishing yin, and the bran-fried Shan Yao is recommended for invigorating the spleen and stopping diarrhea.
- It should not be together used with Cong Bai (Scallion) or Gan Sui (Euphorbia Kansui).
- It should not be taken with alkaline drugs.
- People with dryness-heat, dry stools, or fever due to colds should not take it.
- People who have abdominal distension due to dampness should not take it.