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Milk thistle is a thistle of the genus Silybum, a flowering plant of the daisy family (Asteraceae). The plant is native to the Mediterranean regions of Europe, North Africa and the Middle East. The name "milk thistle" derives from a feature of the leaves, which are prominently banded with splashes of white. Historically, these milky bands were said to be Mother Mary's milk, and this is the origin of another common name, St. Mary's thistle.
Many years of research show the active flavanoid-lignan (flavanolignan) group of constituents, called silymarin, contained only in the seed shell has liver-protective and regenerative properties, as well as antioxidant effects. The liver-protective effects were known and written about in ancient times, leading to the active chemical, pharmacological, and safety research beginning in Germany in the 1950s. Clinical use for a variety of liver ailments, such as hepatitis, has also prospered throughout many parts of the world.
Description and classification
Members of this genus grow as annual or biennial plants. The erect stem is tall, branched and furrowed but not spiny. The large, alternate leaves are waxy-lobed, toothed and thorny, as in other genera of thistle. The lower leaves are cauline (attached to the stem without petiole). The upper leaves have a clasping base. They have large, disc-shaped pink-to-purple, rarely white, solitary flower heads at the end of the stem. The flowers consist of tubular florets. The phyllaries under the flowers occur in many rows, with the outer row with spine-tipped lobes and apical spines. The fruit is a black achene with a white pappus.
Only two species are currently classified in this genus:
Silybum eburneum Coss. & Dur., known as the Silver Milk Thistle, Elephant Thistle, or Ivory Thistle
Silybum eburneum Coss. & Dur. var. hispanicum
Silybum marianum (L.) Gaertner, the Blessed Milk Thistle, which has a large number of other common names, such as Variegated Thistle.
The two species hybridise naturally, the hybrid being known as Silybum × gonzaloi Cantó, Sánchez Mata & Rivas Mart. (S. eburneum var. hispanicum x S. marianum)
A number of other plants have been classified in this genus in the past but have since been relocated elsewhere in the light of additional research.
S. marianum is by far the more widely known species. Milk thistle is believed to give some remedy for liver diseases (e.g. viral hepatitis) and the extract, silymarin, is used in medicine. Mild gastrointestinal distress is the most common adverse event reported for milk thistle. The incidence is the same as for placebo. A laxative effect for milk thistle has also been reported infrequently.
Traditional milk thistle extract is made from the seeds, which contain approximately 4–6% silymarin. The extract consists of about 65–80% silymarin (a flavonolignan complex) and 20–35% fatty acids, including linoleic acid. Silymarin is a complex mixture of polyphenolic molecules, including seven closely related flavonolignans (silybin A, silybin B, isosilybin A, isosilybin B, silychristin, isosilychristin, silydianin) and one flavonoid (taxifolin). Silibinin, a semipurified fraction of silymarin, is primarily a mixture of 2 diastereoisomers, silybin A and silybin B, in a roughly 1: 1 ratio. In clinical trials silymarin has typically been administered in amounts ranging from 420–480 mg per day in two to three divided doses. However higher doses have been studied, such as 600 mg daily in the treatment of type II diabetes and 600 or 1200 mg daily in patients chronically infected with hepatitis C virus. An optimal dosage for milk thistle preparations has not been established. Milkthistle, along with dandelion and other extracts are often referred to as hangover cures as the bitter tincture helps organs rid toxins after heavy drinking.
For many centuries extracts of milk thistle have been recognized as "liver tonics." Research into the biological activity of silymarin and its possible medical uses has been conducted in many countries since the 1960s, but the quality of the research has been uneven. Milk thistle has been reported to have protective effects on the liver and to greatly improve its function. It is typically used to treat liver cirrhosis, chronic hepatitis (liver inflammation), toxin-induced liver damage including the prevention of severe liver damage from Amanita phalloides ('death cap' mushroom poisoning), and gallbladder disorders.
Reviews of the literature covering clinical studies of silymarin vary in their conclusions. A review examining studies with a double-blind protocol concluded that milk thistle and its derivatives has no significant effect on mortality or course of disease in individuals with alcoholic and/or hepatitis B or C disease.
Toxin-induced liver damage
Research suggests that milk thistle extracts both prevent and repair damage to the liver from toxic chemicals and medications. Workers who had been exposed to vapors from toxic chemicals (toluene and/or xylene) for 5–20 years were given either a standardized milk thistle extract (80% silymarin) or placebo for 30 days. The workers taking the milk thistle extract showed significant improvement in liver function tests (ALT and AST) and platelet counts vs. the placebo group.
The efficacy of silymarin in preventing drug-induced liver damage in patients taking psychotropic drugs long-term has been investigated.
A clinical trial in humans showed that silymarin (140 mg orally 3 times daily) was not effective when used for 1 year in combination with ursodeoxycholic acid (UDCA) for the treatment of primary biliary cirrhosis. A study in baboons indicated that continuous intragastric infusion of silymarin retarded the development of alcohol-induced hepatic fibrosis over a 3-year period. The authors suggested that the failure of silymarin to show beneficial effects in other clinical trials may have been due to poor compliance with treatment, resulting in insufficient dosing.
In a 2010 study published in the journal Cancer, milk thistle was associated with a trend towards reducing the liver damaging effects of chemotherapy in a randomized double-blind placebo controlled study of 50 children.
Amanita mushroom poisoning
There has been no controlled clinical study of any treatment suggested for mushroom poisoning. The efficacy of thirty different treatments was analyzed in a retrospective study of 205 cases of Amanita phalloides (death cap) mushroom poisoning. Both penicillin and hyperbaric oxygen independently contributed to a higher rate of survival. When silybin [silibinin] was added to the penicillin treatment, survival was increased even more. In another 18 cases of death cap poisoning, a correlation was found between the time elapsed before initiation of silybin therapy, and the severity of the poisoning. The data appear to indicate that severe liver damage in Amanita phalloides poisoning can be prevented effectively when administration of silybin begins within 48 hours of mushroom intake. Case control studies also suggest that silibinin reduces mortality from mushroom poisoning.
The potential efficacy of silymarin in the treatment of diabetic nephropathy has been demonstrated in several animal studies so far. It has also been found to be effective in reducing proteinuria in type 2 diabetes patients with overt nephropathy in a recent randomized controlled trial. This reduction in proteinuria was attributed to antioxidant and anti-inflammatory effects of silymarin.
Beside benefits for liver disease, other unproven treatment claims include:
Lowering cholesterol levels
Reducing insulin resistance in people with type 2 diabetes who also have cirrhosis,
Reducing the growth of cancer cells in breast, cervical, and prostate cancers.
Clinical study has shown that liver function tests can be improved in active hepatitis patients.
Use as food
Milk thistle has also been known to be used as food. Around the 16th century the milk thistle became quite popular and almost all parts of it were eaten. The roots can be eaten raw or boiled and buttered or par-boiled and roasted. The young shoots in spring can be cut down to the root and boiled and buttered. The spiny bracts on the flower head were eaten in the past like globe artichoke, and the stems (after peeling) can be soaked overnight to remove bitterness and then stewed. The leaves can be trimmed of prickles and boiled and make a good spinach substitute or they can also be added raw to salads.