Pueraria: Source of Important Isoflavones
Background: the herb and its constituents
Pueraria (gegen), the root of Pueraria lobata, is a commonly used herb in Chinese medicine. It is perhaps better known by its Japanese name: kudzu. It is a fast growing vine that can extend a foot in length each day during the warm season. Its root is also fast growing, typically reaching 50 pounds or more, and can attain a weight of 400 pounds (about 2/3 of it is water). Aside from the use of pueraria as an ingredient in traditional Chinese medicine formulas, mainly those from the ancient Shanghan Lun, it is the source of a food ingredient widely used in Japan: its starch. Kudzu starch has a mild taste that doesn’t conflict with delicate and subtle flavors; it creates a smooth consistency; and it crisps well when used as a coating for deep fried foods. Before isolating the starch (which is 99.6% starch with about 0.4% water), the whole roots also have a small amount of protein and are a reasonably good source of calcium, magnesium, iron, potassium, and zinc when compared to starchy foods such as wheat and sorghum.
Pueraria has one major medicinal active component group: isoflavones that are often simply designated as puerarin, which is its main ingredient (chemical structure, right). Although several isoflavones have been isolated and characterized, there are five principal ones: puerarin, methylpuerarin, daidzein, daidzin, and daidzein glucopyranoside. Both daidzein and daidzin are also found in soy beans, which are known for their content of two other isoflavones, genistein and genistin (these isoflavones appear to be primarily responsible for soy’s benefits in alleviating menopausal symptoms; pueraria contains little of these two components). The total isoflavone content of the dried pueraria root slices generally is typically around 1%, and may reach 2%. By contrast, the main dietary source of isoflavones, soybeans, usually do not exceed 0.6% isoflavones and more typically contain about 0.3% of this component. Isoflavones are almost exclusively found in the Fabaceae Family, including the Chinese herbs pueraria, soja (soybeans), astragalus, licorice, sophora, and millettia.
The pueraria isoflavones were intensively researched in China during the 1970’s, and developed into a drug-like product that is used for circulatory disorders. The tablet or injection (given as IV drip) of concentrated pueraria isoflavones is used to treat dizziness, headaches, neck pain, sudden deafness, glaucoma, diabetic retinopathy and hearing loss, angina, heart attack, myocarditis, and symptoms of hypertension (1,2). More recently, pueraria isoflavones have been examined for neuroprotective effects; as an example, it was indicated that administration of aspirin plus puerarin after a stroke had improved neurological function (3). Laboratory animal investigation suggests that puerarin may help reduce glutamate damage to axons (4). The uses of pueraria and its isoflavones are somewhat like those of ginkgo leaf flavonoids, crataegus flavonoids, and hippophae (sea buckthorn) flavonoids; the first is known for promoting circulation to the brain and the latter two are used for promoting cardiac circulation.
Dosage and Effect
Using the appropriate dosage of the crude herb, as indicated in traditional texts, can be elaborated from work done with isolated active components in a standard dosage form. As examples of clinical applications (5), pueraria flavones were given in tablets at a dose of 30–40 mg each time, three times daily (total daily dose is 90–120 mg) to 191 patients with coronary heart disease and angina pectoris; in the treatment of hypertension, 50 mg of pueraria flavones given twice per day (total daily dose is 100 mg) for several weeks; similarly, hypertensive patients suffering from angina were given a daily dose of pueraria flavones at 150 mg/day. From a survey of such applications for the tablets, the maximum daily dose recommended appears to be 300 mg/day. However, this upper level is apparently not because of toxicity, but simply an amount that was indicated as effective for the particular applications. Recently, work done with puerarin injection has involved 400 mg for a single injection treating diabetic retinopathy (6) and 500 mg in a single injection for heart attack patients (7).
At a maximum level of 2% isoflavones in the dried pueraria roots, to get a dosage in the range of about 100–500 mg of this component, one would use 5–25 grams in decoction. However, the level of isoflavones is more typically only about 1%, so that a dose of 10–50 grams would be more suitable. Since the higher dosages are given by injection for serious and acute conditions, the suggested decoction range for most applications would be 10–30 grams of dried root for a one day supply. In a report on the treatment of diabetic hearing loss (8), the treatment group received a decoction for which the basic recipe included pueraria at 30 grams per day.
The Materia Medica guides published in China, dosage recommendations range from 5–24 grams in decoction, which is thus on the low side, but when the herb is blended in formulas, as is common, additional flavonoids are usually obtained from one or more of the other ingredients. The low doses of pueraria root (e.g., 3-9 grams) as used in some large traditional formulas may have limited effect. It is possible that when combined with licorice root (which is common in these formulations), the isoflavone components of these two herbs work together to alleviate inflammation, thus allowing the low dose of pueraria to contribute to the action of the formula. A good summary suggestion is found in Oriental Materia Medica (9), where the recommended dosage range for pueraria roots in decoction is 6–24 grams, and the recommended dosage of the pueraria flavonoid is 100–300 mg/day.
The herb has very low toxicity, as demonstrated by the fact that the isoflavone extract of pueraria has even been used as an IV drip without reported adverse effects. The authors of a report (10) on use of puerarin IV drip for heart disease patients concluded: “Puerarin is a safe and effective drug in treating patients with unstable angina and worth spreading in clinical usage.” The authors of a review of pueraria flavonoids (11), based on work from several institutes in Beijing and Chengdu, stated that they “recently prepared [puerarin] in an 80+% concentration that shows little toxicity, benefits cardio-cerebro vascular disease, and has good absorption when taken orally. It has passed pre-clinical examination for new drugs in accordance with criteria established by the Health Ministry of the People’s Republic of China, and is presently in clinical trials.”
Pueraria isoflavones are rapidly absorbed from the GI tract, but are also rapidly eliminated (12). This high turn-over indicates the need for frequent dosing when using the oral form at moderate dosage, such as three times a day, to maintain significant blood levels for the desired effects on circulation.
Conditions determining what form to use
A limiting factor in use of high dosage pueraria in decoctions is that the starch turns the decoction quite thick, especially if it is allowed to cool. In China, because of the availability of puerarin in pill form, this herb is not often included in decoctions. The change in practice may have come also as a result of recognizing the need for higher dosage and the shift of applications from alleviating symptoms of the common cold (as fit some of the early concepts of its use) to treating serious cardiovascular diseases.
In sum, China’s use of pueraria in recent years is tending towards less frequent administration in traditional style decoction formulas (or dried decoctions), relying more heavily on the form of concentrated extracts of the isoflavone fraction taken in daily doses of 100–300 mg puerarin per day orally or by IV drip with doses up to 500 mg. The herb can still be utilized in traditional decoction formulas with good effect especially if incorporated at a dose of about 15–18 grams/day (about 3.0-3.6 grams of dried decoction). The isoflavones are the key ingredient of pueraria roots that influences the determination of proper dosage.