Milk Thistle
by Dr. Dean Gray

"If plants were as simple as the physiologist might wish, there would be nothing left to do." This quote from William S. Hillman describes the reductionist approach a scientist is sometimes required to take in order to measure a discrete phenomenon; while it also conveys the enjoyment in discovering the unknown.

Medicinal plants, even those that have been widely studied, still contain secrets that have yet to be uncovered.

Milk thistle (Silybum marianum (L.) Gaertn.) seeds contain several compounds that are produced from the coupling of a flavonoid and a lignan (flavonolignans). Flavonoids and lignans are sub-classes of plant phenolics (compounds that possess a six-carbon aromatic ring). There are approximately 8,000 known phenolics, nearly half of which are flavonoids.1 All of the flavonoids are antioxidants, and many have antibacterial, antimicrobial and anti-inflammatory activities as well. Lignans are found predominantly in woody plant tissue, and have shown antifungal 2, and analgesic 3 activities.

The predominant Milk Thistle flavonolignans include silybin and isosilybin (each of which is a mixture of two isomers), silychristin, and silydianin. Collectively, these compounds are known as silymarin. The unique properties of silymarin can inhibit the absorption of toxins into the liver, and because the compounds are also phenolics, they are effective antioxidants.

Milk Thistle medicines are generally prepared from the seeds, which can vary substantially in color from milky white to nearly black as they develop towards maturity. Given that certain flavonoids and most lignans exist in woody tissues (like a seed coat), we hypothesized that seed color (i.e., seed maturity) may be correlated to either silymarin, and/or taxifolin content, another prevalent flavonoid believed to be one of the synthetic starting points for the silymarin compounds. Recently, Herb Pharm’s Analytical Lab completed a study comparing the silymarin and taxifolin content of different colored milk thistle seeds.

Milk Thistle seeds were separated into color gradients from the lightest to the darkest in color, and analyzed using high performance liquid chromatography. The results showed that as the seed matured and color became darker, silymarin content increased by approximately 25%, a statistically significant amount. In addition, taxifolin differed most dramatically between treatments, where the darker seeds contained an average of 226% greater concentration than the lighter colored seeds. From these results, we are able to scientifically justify our exclusive use of dark, fully-ripened milk thistle seeds, harvested at their peak of natural potency.

References
1. Harborne JB. Phytochemical Dictionary. Second Edition. (Eds. JB Harborne, H Baxter, and GP Moss). Taylor & Francis Ltd, London. 1999, pp. 976.
2. Pauletti PM, Araujo AR, Young MC, Giesbrecht AM, Bolzani VD. nor-Lignans from the leaves of Styrax ferrugineus (Styracaceae) with antibacterial and antifungal activity. Phytochemistry. 2000, 55(6):597-601.
3. Borsato ML, Grael CF, Souza GE, Lopes NP. Analgesic activity of the lignans from Lychnophora ericoides. Phytochemistry. 2000, 55(7):809-13.