Milk Thistle's Liver-Protective Properties

Milk Thistle's
Liver-Protective Properties

This section is compiled by Frank M. Painter, D.C.
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From The October 1999 Issue of Nutrition Science News

By Lise N. Alschuler, N.D.

In an increasingly toxic world, we place growing burdens on the body's detoxification system, the hub of which is the liver. Millions of compounds are detoxified within each liver cell, or hepatocyte. Inevitably, this wear and tear compromises liver cells and surrounding connective tissue. Hepatotoxicity is fast becoming a major health issue. In fact, many practitioners believe poor liver function caused by toxin accumulation or by liver-function decline may contribute to other seemingly unrelated illnesses, such as rheumatoid arthritis, eczema, migraine headaches and premenstrual syndrome, and may manifest symptoms of its own. As a result, milk thistle (Silybum marianum) is widely prescribed by herbalists throughout Europe and the Americas for liver protection.

Milk thistle, also known as St. Mary's thistle and lady's thistle, is native to Asia Minor, North Africa, southern Europe and southern Russia. It has been naturalized to central Europe, North and South America, and South Australia. The herb has dark-green prickly leaves mottled or streaked with white veins, blooms from June to September and can grow to six feet tall. Its medicinal properties are found in the small, hard fruits, sometimes called seeds but known technically as achenes, that appear after the plant flowers.

Milk thistle fruits contain a mixture of flavonolignans--a unique group of carbohydrates that share a common chemical structure. These flavonolignans, the plant's active constituents, are known collectively as silymarin. Silymarin usually comprises about 1.5 to 3 percent of the fruit and contains silybinin, the major constituent, along with isosilybin, dihydrosilybin, silydianin, silychristin, and probably a few flavonoids. The fruits also contain 20 to 30 percent fixed oil (a combination of fatty acids that are solid at room temperature), mucilage, protein and taxifolin (a chemical with unknown significance).

Although milk thistle's mechanism of action has not been fully explained, the herb has a long history of use as a liver protectant and liver decongestant. (A liver decongestant stimulates bile flow through the liver and gallbladder, thus reducing stagnation and preventing gallstone formation and bile-induced liver damage.) Pharmacological investigations have centered on silymarin, which is most notable for its antihepatotoxic activity. This effect has been demonstrated against a variety of potent liver toxins including those from the death cap mushroom (Amanita phalloides). [1, 2] S. marianum extract works as both a preventive and antidote for death cap mushroom poisoning. Intravenous administration up to 48 hours after ingestion is effective. [3]

Finnish researchers conducted a double-blind, controlled study to look at the effect of milk thistle fruit extract on liver inflammation. They measured levels of serum transaminase, an enzyme released from inflamed liver cells, in 97 patients. All subjects reportedly abstained from alcohol during the four-week study during which they received either a 420 mg daily dose of standardized S. marianum extract (Legalon, manufactured by Madaus AG of Germany) or placebo. Subjects who received the extract showed a statistically significant decrease in liver enzymes compared with those taking placebo. [4]

In a larger clinical trial, researchers assessed the benefits of milk thistle extract on 170 patients, 91 of them alcoholics with liver cirrhosis. Subjects received 140 mg silymarin three times daily for 41 months. The four-year survival rate was 58 percent in the silymarin group and 39 percent in the placebo group--a difference of 19 percent. The reduced death rate among those taking silymarin was most pronounced in the alcoholic cirrhosis subgroup. There were no side effects from silymarin. [5] This study is significant for several reasons. The results support the idea that long-term treatment with milk thistle extract is beneficial and not likely to be harmful. These results also suggest milk thistle extract may be particularly effective for patients with alcohol-induced liver damage.

In all, studies suggest S. marianum protects the liver. It is prescribed for any condition of threatened or obvious hepatotoxicity including chronic daily exposure to environmental pollutants, toxic effects of viral hepatitis, toxic side effects of certain medications, toxicity from chronic alcohol use, cirrhosis and fatty degeneration of the liver. Milk thistle extract should help improve liver function, protect hepatocytes and increase bile flow for anyone with these conditions. [6] The antihepatotoxic effects are quite pronounced while the liver-decongesting and bile-stimulating effects are mild and gentle. This herb is extremely well tolerated.

Milk thistle is effective in a variety of preparations, though the traditional one is a medicinal tea or decoction. Silymarin is poorly soluble in water but historical use indicates its bioavailability increases if the crushed fruits are soaked overnight before being boiled for 15 minutes. A therapeutic tea contains 1 to 3 tablespoons of crushed fruits per 8 to 10 ounces of water. Another preparation is alcohol and water extraction, commonly known as a tincture. Encapsulated standardized milk thistle extract is the preparation studied in clinical trials. Extracts are typically standardized to 70 percent of the silymarin complex. The typical dose is 200 to 420 mg daily taken in three divided doses with meals for eight weeks, then 280 mg/day in three divided doses. There are no known side effects or contraindications, and this herb is safe for use during pregnancy and lactation.

Milk thistle can be taken as a preventive measure, particularly if a person eats chemically processed foods, is exposed regularly to foreign compounds that require detoxification, has a known liver disease or family history of liver disease, or drinks alcohol regularly. Long-term continued use has no known side effects or contraindications. Recommend that customers discontinue use for two to seven days every eight weeks to maintain effectiveness, as they should with any herbal medicine.

Pollutants, toxic medications and exposure to infectious organisms underscore the need for liver protection. Milk thistle offers a reliable and safe solution.

Lise N. Alschuler, N.D., received her degree from Bastyr University, Bothell, Wash., where she is currently the clinical medical director. She also has a private practice in Seattle.

Commission E Monograph

Milk Thistle fruit

Name of drug: Cardui mariae fructus, milk thistle fruit

Composition of drug: Milk thistle fruit consists of ripe seed of Silybum marianum (L.) Gaertner [Fam. Asteraceae], freed from the pappus, and its preparations in effective dosage. The drug contains silibinin, silydianin and silychristin.

Uses: Crude drug--dyspeptic [digestive] complaints. Formulations*--toxic liver damage; for supportive treatment in chronic inflammatory liver disease and hepatic cirrhosis.

Contraindications: none known

Side effects: Crude drug--none known; Formulations--a mild laxative effect has been observed in occasional instances.

Interactions with other drugs: none known

Dosage: Unless otherwise prescribed, average daily dose of drug is 12 to 15 g; formulations equivalent to 200 to 400 mg of silymarin, calculated as silibinin. Mode of administration: Powdered drug for making infusions and other galenical formulations to be taken by mouth.

Actions: Silymarin acts as an antagonist in many experimental liver-damage models: phalloidin and -amanitin (death-cap toxins), lanthanides, carbon tetrachloride, galactosamine, thioacetamide, and the hepatotoxic virus FV3 of cold-blooded vertebrates.

The therapeutic activity of silymarin is based on two sites or mechanisms of action: a) it alters the structure of the outer cell membrane of the hepatocytes in such a way as to prevent penetration of the liver toxin into the interior of the cell; b) it stimulates the action of nucleolar polymerase A, resulting in an increase in ribosomal protein synthesis, and thus stimulates the regenerative ability of the liver and the formation of new hepatocytes.

*Note: "Formulation" refers to an extract standardized to at least 70 percent silymarin, the collective name for the three compounds listed in the "Composition of drug" section above.

Reprinted with permission from The Complete German Commission E Monographs--Therapeutic Guide to Herbal Medicines, a 700-page guide featuring 380 monographs. The guide is published by the American Botanical Council, Austin, Texas, 1998.
  1. Faulstich H, et al.
    Silybin inhibition of amatoxin uptake in the perfused rat liver.
    Arzneim-Forsch Drug Res 1980; 30: 452-4

  2. Tuchwever B, et al.
    Prevention of silybin of phalloidin induced acute hepatoxicity.
    Toxicol Appl Pharmacol 1979; 51: 265-75

  3. Hruby K, et al.
    Effect of the flavolignans of Silybum marianum L. on lipid peroxidation in rat liver microsomes and freshly isolated hepatocytes.
    Pharmacol Res 1992; 25: 147-54

  4. Salmi H, Sarna S.
    Effect of silymarin on chemical, functional, and morphological alterations of the liver.
    Scand J Gastroenterol 1982; 17: 517-21

  5. Ferenci P, et al.
    Randomized, controlled trial of silymarin treatment in patients with cirrhosis of the liver.
    J Hepatol 1989; 9: 105-13

  6. Nassauto G, et al.
    Effect of silibinin on biliary lipid composition: experimental and clinical study.
    J Hepatol 1991; 12: 290-5


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