– Milk Thistle – Milk thistle (Silybum marianum) is an edible plant that has been used medicinally for more than 2,000 years and is widely prescribed by herbalists with almost no known side effects. Milk thistle is native to the Mediterranean and grows wild throughout Europe and North America. It also grows in India, China, South America, Africa and Australia. Several European sources use wild crafted milk thistle from Eastern Europe. The dried seeds from the milk thistle extract contain approximately 60 percent silymarin. Silymarin is a highly concentrated extract of milk thistle seed and is responsible for its many health benefits. It contains up to 80 percent flavanolignans (compound of flavonoids) and is a mixture of silybin (also known as silybinin), silychristin, and silydianin (collectively described as silymarin). Silybin is the most prevalent and accounts for about 50–60 percent of the silymarin. It is also the most biologically active with regard to antioxidant, cytoprotective and hepatoprotective actions. Silymarin content often varies between 1–3 percent (seed with 3–6% silymarin is considered of high quality). Milk thistle seed also contains 20–30 percent oils/lipids (60% linoleic acid, 30% oleic acid), flavonoids (taxifolin and quercetin) and 20–30 percent protein. These ingredients also contribute to milk thistle’s therapeutic actions. Milk Thistle Extracts Silymarin is typically extracted with 95 percent ethyl alcohol. The extraction process may also include filtration (with water), evaporation and may also include pressing and heat drying. There is often poor documentation of the source, ingredients and extraction process of commercial silymarin products. A few companies state that they use purified water and ethanol extraction without harmful solvents. Some companies carefully examine sources of raw milk thistle and use chromatography to optimize quality and to separate the phytochemicals in the extract into individual components. Some product is manufactured according to good manufacturing practice (GMP) standards. Various amounts of raw herb are used in extracts. One Australian company uses a 70:1 extract. They begin with 14.7 grams of milk thistle herb and create a tablet of 210 mg. Other companies use 30:1 or 40:1 extracts. German research initially led to a standardized milk thistle extract of 70 percent silymarin. Current standardized silymarin extracts contains 70 to 80 percent silymarin. Standardized or quantified extracts of milk thistle are often expressed as “standardized to 80 percent silymarin” or “calculated as silybin.” Herbs contain a wide variety of phytochemicals and supporting evidence for the effectiveness of an herbal product is often based on use of the whole herb or the full-spectrum extract. When an herbal extract is standardized to contain 80 percent silymarin, the process of standardization can encourage a manufacturer (by using various solvents) to produce an herbal extract that only focus on the one active ingredient or marker compound while ignoring the remaining phytochemical profile of the herb. This process changes the properties of the herbal preparation, and therefore raises questions about the product’s efficacy. From standardized silymarin, silybin can be isolated and combined on a molecular level with phosphatidylcholine. This formulation, called IdB 1016 (from Idena in Italy), is available as Siliphos, Silipide or Silybin Photosome. Siliphos is the complex of one part silybin and two parts phosphatidycholine from soybean phopholipids (lecithin), for which standardization is expressed as “silybin equivalents.” The term “phytosome” refers to binding molecules of an herbal compound to molecules of phosphatidylcholine creating a new molecule (phytosome). Pharmacokinetics, Bioavailability and Absorption
Pharmacokinetic studies have shown that silymarin is absorbed by the oral route and that it distributes into the digestive tract (liver, stomach, intestine, and pancreas). Absorption of silymarin from the gastrointestinal tract is about 20 to 50 percent – thus bioavailability is low. It is reported that absorption decreases with age and may only be 10 percent when 60 years old. Peak plasma concentrations are achieved somewhere between 90 minutes and 4 hours. Approximately 80 percent of silymarin is excreted in the bile and, to a lesser degree, in the urine. Its elimination half-life ranges from 6 to 8 hours. Milk thistle extracts, although standardized on silymarin content, differ regarding the release of silymarin or silybin; as a result, the availability of silybin for absorption differs. It seems to depend on several factors such as the content of accompanying substances with an ability to become more soluble (such as other flavonoids, amino acids, proteins and fats found in the extract), the concentration of the extract itself and various harvesting processes (including growth conditions such as fertilizer used, water, and field capacity). Also, due to the fact that there are different varieties of milk thistle (identified by chromatography); there are differences in absorption and oral bioavailability. Legalon and Siliphos Reviewing studies of silymarin preparations (not including Siliphos), release of silybin from Legalon (manufactured by Madaus in Germany) was more rapid and higher compared with other preparations. Pharmacokinetic studies indicate that Siliphos when taken orally has better absorption from the gastrointestinal tract and, as a result, is more bioavailable than some standardized silymarin. Studies have shown that the bioavailability of silybin in Siliphos is approximately tenfold greater than the silybin content of other standard milk thistle preparations. In addition, studies have reported that silybin concentrations in patient bile after Siliphos administration were several-fold higher than after oral silymarin. Other preparations Because silymarin is poorly soluble in water, teas are considered to have a less than 10 percent bioavailability. Oral tinctures, or alcohol-extracted preparations, are considered suboptimal, and effective oral therapy is assumed to require concentrated products. It has been reported that the absorption of silymarin in enhanced by adding lecithin. Researchers from Italy reported that a silybin beta-cyclodextrin complex (named IBI/S) increased bioavailability of silybin. This research is limited and may or may not be of any significance. Interpreting data from studies There is difficulty in interpreting available data from human studies. Most studies were done to establish clinical results and the various herbal preparations and products were not a primary concern. The quality of many study designs and published reports has been lacking in regard to quality of product; the number of reliable studies is also low. Milk Thistle Preparations and Doses The most common oral formulation is capsules containing powdered seed extract. Other concentrated oral formulations include tablets and softgel capsules. Dosages for milk thistle are based on silymarin content Most milk thistle marketed in the United States is sold as a dietary supplement containing 200 milligrams of a concentrated extract standardized to 80 percent silymarin. Taking silybin is considered to be the optimal way of obtaining the benefits of silymarin, so one may want to consider an extract that contains 80 percent silybin. Researchers have not yet identified the optimal dose of silymarin The typical adult dosage for silymarin is 240 to 800 mg/day in two or three divided doses. It's noted that a supplement containing at least 240 mg per day of silymarin would be helpful for most people. Doses of 150 to 300 mg per day are considered sufficient to increase the liver's production of the protective antioxidant glutathione. Higher doses are needed for chronic liver disease: 140 to 210 mg of silymarin, three times daily in a standardized extract form (total 420 to 630 mg/day). Simultaneous dosing with a lecithin supplement has been recommended to increase absorption. For Siliphos, 240 mg, three times daily is recommended. Older patients require a higher dose due to age related decrease in absorption abilities. Reviewing the doses that were used in milk thistle human research, the dose varied from 240 to 800 milligrams per day. A few studies used Siliphos at 240 mg. Toxicity Human studies have shown silymarin to be generally without side effects. The typical adult dosage for silymarin is 240 to 900 mg/day in two or three divided doses. At higher doses (>1500 mg/day) silymarin may produce a laxative effect due to increased bile flow and secretion. Mild allergic reactions have also been noted. Traditional vs. Pharmacological Approach to Herbology When considering different approaches to herbs it is important to recognize the difference between the traditional (including Chinese) approach and the Western pharmacological approach. Traditional herbology favors ingesting the whole herb. Western pharmacologists take an herb, find the active ingredient for treating a certain disease, and extract it; thus reducing the herb to its active ingredients. Using this knowledge we can compare traditional milk thistle herbal extracts to the pharmacological approach represented by Siliphos (using only a silybin extract). We have milk thistle seed extracts that have been standardized to 80 percent silymarin; these include different products that use extract ratios of raw milk thistle seed to extract of between 30:1 and 70:1. In addition, several companies integrate the ideologies of both traditional herbalism and standardized herbal technology. To ensure consistent and reliable phytonutrient levels, they isolate a controlled amount of active plant compounds. Then, they blend these enhanced "standardized" compounds with the components that occur naturally in the whole raw herb. We compare this to the Siliphos phytosome product that contains molecules of silybin. Summary We can summarize our findings by mentioning three major areas: active ingredients, bioavailability and approaches to herbalism. Silymarin and specifically silybin are the active ingredients in milk thistle seed. Products with higher levels of these ingredients would be preferred to insure greater bioabailabity. Various studies that compared Siliphos to other silymarin products reported better bioavailability for the phosphatidylcholine-silybin compound. Studies that compare various (non-Siliphos) silymarin products for bioavailability are limited or not available. Traditional herbalism favors using herbal extracts from the raw herb; in this case from the milk thistle seed. Quality and purity of the herb is extremely important and more documentation is needed from manufactures including knowledge that the product was prepared according to good manufacturing practice standards. Selected Milk Thistle Products
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