Silymarin (Milk Thistle Fruit Extract): Definition, Metabolism, Bioavailability

Silymarin is a fruit extract and comes from milk thistle (Silybum marianum). This medicinal plant belongs to the composite family (Asteraceae), subfamily Carduoideae. With a stem height of 20 cm to 150 cm, the annual to biennial herb is easily recognizable by its white-green marbled leaves and purple flower. Milk thistle grows preferentially on dry, stony soil and is found in North Africa, Asia Minor, southern Russia and the Mediterranean region. This plant is cultivated and grown in Austria, Hungary, Germany, Argentina, Venezuela and China. The black-brown fruits of milk thistle consist of 20% to 30% fat-rich oil with a high linoleic acid content, 25% to 30% protein, 1.5% to 3% silymarin, as well as phytosterols and mucilage. The resulting silymarin complex consists of the flavanolignans silybin (or silibinin), silicristin, silidianin, isosilibin and the flavanonol taxifolin. At 40% to 70%, silybin makes up the largest proportion and has the highest biological activity.

Metabolism

After oral intake, silymarin is absorbed by 20% to 50%. The flavanolignans are conjugated with sulfate and glucuronic acid in the liver and then enter the plasma and bile. After 4 to 6 hours, the maximum plasma concentration is reached at 1.3 µg/ml to 1.7 µg/ml.80% of silymarin is excreted in bile and approximately 10% enters the enterohepatic circulation (intestinal-liver circulation).

Bioavailability

The bioavailability of silymarin is low and depends on the concentration as well as the presence of other ingredients (such as flavonoids, phenolic derivatives, proteins, tocopherols, etc.). The addition of phosphatidylcholine or ß-cyclodextrin makes silymarin more bioavailable.