Milk thistle extract: properties, uses, pros, cons, safety

Milk thistle (Silybum marianum) is a short-lived perennial or biennial herbaceous plant belonging to the botanical family Asteraceae. It is characterized by a sturdy stem, large green leaves with distinctive white marbled veins and spiny margins, and purple flower heads surrounded by spiny bracts. It grows wild in many areas of the Mediterranean basin and is cultivated mainly for its seeds.

As a food ingredient, milk thistle is used primarily for its achenes (seeds), whole or ground, and for milk thistle seed oil obtained by pressing. The seeds can be used in small amounts in herbal tea blends, added to bread and baked goods, or as a topping for salads and grain-based dishes. The oil, with a delicate, slightly herbaceous taste, is generally used raw to dress salads or cold dishes. Both seeds and oil contain a lipid fraction and phenolic compounds typical of the species, and milk thistle is also traditionally regarded as a medicinal plant.

Botanical Classification

• Kingdom: Plantae
• Order: Asterales
• Family: Asteraceae
• Genus: Silybum
• Species: S. marianum

Plant Characteristics

• Height: Typically grows to 1-1.5 meters (3-5 feet).
• Leaves: Large, lobed, and spiny, with dark green coloration and silver streaks due to the presence of vein-like markings.
• Flowers: Purple or pink, arranged in capitula, blooming in summer.
• Fruits: Achenes covered with a spiny involucre.

Chemical Composition and Structure

Silybum marianum contains a range of bioactive compounds, most notably silmarin, which is a group of flavonolignans with significant medicinal properties:

• Silymarin: The primary active compound, consisting mainly of:

  • Silybin (Silibin): The most studied flavonolignan, known for its potent antioxidant, hepatoprotective, and anti-inflammatory properties. It is primarily responsible for the liver-supporting effects of Milk Thistle.
  • Silibinin: An isomer of silybin, also contributing to the hepatoprotective effects.
  • Silydianin: Contributes to the antioxidant and anti-inflammatory properties of silymarin.
  • Silycristin: Present in smaller amounts, it has antioxidant effects and supports liver function.

• Phenolic Acids: Including caffeic acid and ferulic acid, known for their antioxidant properties.

• Flavonoids: Such as apigenin and luteolin, which provide additional antioxidant and anti-inflammatory benefits.

How to Cultivate It

• Climate: Prefers temperate and Mediterranean climates. Can be grown in cooler climates but is sensitive to frost.
• Soil: Requires well-drained, nutrient-rich soil with a pH between 6.0 and 7.5.
• Light: Needs full sun exposure for optimal growth.
• Watering: Regular watering is necessary during growth; however, it is drought-tolerant once established.
• Propagation:
  • From Seeds: Sow seeds in spring or early summer. Seeds should be planted superficially and kept moist until germination, which takes 2-4 weeks.
  • From Cuttings: Less common, but possible. Cuttings should be rooted in a moist, well-drained substrate.

Uses and Benefits

• Medicinal Uses:

  • Liver Protection: Milk Thistle is used to improve liver function and treat liver disorders such as fatty liver disease and hepatitis.
  • Antioxidant: Silymarin neutralizes free radicals and reduces oxidative stress.
  • Anti-inflammatory: Reduces inflammation and supports general health.

• Dietary Uses:

  • Supplements: Milk Thistle extracts are commonly used in dietary supplements for liver support.
  • Teas and Decoctions: Leaves and seeds can be used to make infusions beneficial for digestion.

• Cosmetic Applications:

  • Skincare: Extracts are included in skincare products for their antioxidant and regenerative properties.
  • INCI Functions:

Skin protectant. It creates a protective barrier on the skin to defend it from harmful substances, irritants, allergens, pathogens that can cause various inflammatory conditions. These products can also improve the natural skin barrier and in most cases more than one is needed to achieve an effective result.

Skin conditioning agent. It is the mainstay of topical skin treatment as it has the function of restoring, increasing or improving skin tolerance to external factors, including melanocyte tolerance. The most important function of the conditioning agent is to prevent skin dehydration, but the subject is rather complex and involves emollients and humectants that can be added in the formulation.

Applications

• Traditional Medicine: Widely used in herbal medicine for its hepatoprotective and antioxidant properties.
• Cosmetics: Incorporated into skincare products for its antioxidant and anti-inflammatory effects.
• Health and Wellness: Used as a dietary supplement to support liver function and overall well-being.

Environmental and Safety Considerations

• Environmental Impact: Generally non-invasive and suitable for cultivation without significant negative environmental effects.
• Safety:
  • General Safety: Considered safe when used as directed. Potential for allergic reactions and interactions with liver medications and anticoagulants. Consult a healthcare provider if you have pre-existing conditions or are taking other medications.

INCI Functions:

• Silybum Marianum (Milk Thistle) Extract: Antioxidant, anti-inflammatory, hepatop

Some interesting flavonolignans are present in the bark: silibinin, isosilybin, silydianin, and silychristin (1). 

Flavonolignans are composed of flavones and lignans and exert antioxidant and hepatoprotective activity.

Silymarin studies

References________________________________________

Lee J. I., Narayan M., Barrett J. S. Analysis and comparison of active constituents in commercial standardized silymarin extracts by liquid chromatography-electrospray ionization mass spectrometry. Journal of Chromatography B. 2007;845(1):95–103. doi: 10.1016/j.jchromb.2006.07.063.

Abstract. A sensitive method for the simultaneous quantitation of six active constituents in commercial silymarin standardized extracts was developed based on liquid chromatography (LC) in combination with mass spectrometry (MS). The six main active constituents, namely, silydianin, silychristin, diastereoisomers of silybin (silybin A and B), and diastereoisomers of isosilybin (isosilybin A and B) were completely separated and quantified by LC/MS. Silymarin obtained from Sigma-Aldrich Co. was evaluated and used as standard reference material for the six individual constituents in comparing the relative content of silymarin and the relative ratio of each constituent in commercial standardized silymarin extracts, respectively. Significant variation was found between different commercial silymarin sources. As a result, this method has proven useful in evaluating and quantifying the six active constituents in commercial milk thistle extracts. The calibration curves were over the range from 0.25 to 100 microg/mL for silychristin and silydianin, and from 0.10 to 100 microg/mL for silybin A, silybin B, isosilybin A and isosilybin B, respectively (r(2)> or =0.9958). For all six active constituents, the overall intra-day precision values, based on the relative standard deviation replicate for four QC levels, ranged from 1.18% to 12.4% and accuracy ranged from 89.4% to 112%. This methodology could easily be incorporated into standardized testing to assess content uniformity including lot-to-lot variation as part of routine process controls as well as a means to describe cross-product variation among the exiting marketed formulations.

Wang X, Zhang Z, Wu SC. Health Benefits of Silybum marianum: Phytochemistry, Pharmacology, and Applications. J Agric Food Chem. 2020 Oct 21;68(42):11644-11664. doi: 10.1021/acs.jafc.0c04791.

Abstract. Silybum marianum (SM), a well-known plant used as both a medicine and a food, has been widely used to treat various diseases, especially hepatic diseases. The seeds and fruits of SM contain a flavonolignan complex called silymarin, the active compounds of which include silybin, isosilybin, silychristin, dihydrosilybin, silydianin, and so on. In this review, we thoroughly summarize high-quality publications related to the pharmacological effects and underlying mechanisms of SM. SM has antimicrobial, anticancer, hepatoprotective, cardiovascular-protective, neuroprotective, skin-protective, antidiabetic, and other effects. Importantly, SM also counteracts the toxicities of antibiotics, metals, and pesticides. The diverse pharmacological activities of SM provide scientific evidence supporting its use in both humans and animals. Multiple signaling pathways associated with oxidative stress and inflammation are the common molecular targets of SM. Moreover, the flavonolignans of SM are potential agonists of PPARγ and ABCA1, PTP1B inhibitors, and metal chelators. At the end of the review, the potential and perspectives of SM are discussed, and these insights are expected to facilitate the application of SM and the discovery and development of new drugs. We conclude that SM is an interesting dietary medicine for health enhancement and drug discovery and warrants further investigation.

Bijak M. Silybin, a Major Bioactive Component of Milk Thistle (Silybum marianum L. Gaernt.)-Chemistry, Bioavailability, and Metabolism. Molecules. 2017 Nov 10;22(11):1942. doi: 10.3390/molecules22111942.

Abstract. Milk thistle (Silybum marianum) is a medicinal plant that has been used for thousands of years as a remedy for a variety of ailments. The main component of S. marianum fruit extract (silymarin) is a flavonolignan called silybin, which is not only the major silymarin element but is also the most active ingredient of this extract, which has been confirmed in various studies. This compound belongs to the flavonoid group known as flavonolignans. Silybin's structure consists in two main units. The first is based on a taxifolin, the second a phenyllpropanoid unit, which in this case is conyferil alcohol. These two units are linked together into one structure by an oxeran ring. Since the 1970s, silybin has been regarded in official medicine as a substance with hepatoprotective properties. There is a large body of research that demonstrates silybin's many other healthy properties, but there are still a lack of papers focused on its molecular structure, chemistry, metabolism, and novel form of administration. Therefore, the aim of this paper is a literature review presenting and systematizing our knowledge of the silybin molecule, with particular emphasis on its structure, chemistry, bioavailability, and metabolism.

Pickova D, Ostry V, Toman J, Malir F. Presence of Mycotoxins in Milk Thistle (Silybum marianum) Food Supplements: A Review. Toxins (Basel). 2020 Dec 8;12(12):782. doi: 10.3390/toxins12120782. 

Abstract. The consumption of herbal-based supplements, which are believed to have beneficial effects on human health with no side effects, has become popular around the world and this trend is still increasing. Silybum marianum (L.) Gaertn, commonly known as milk thistle (MT), is the most commonly studied herb associated with the treatment of liver diseases. The hepatoprotective effects of active substances in silymarin, with silybin being the main compound, have been demonstrated in many studies. However, MT can be affected by toxigenic micro-fungi and contaminated by mycotoxins with adverse effects. The beneficial effect of silymarin can thus be reduced or totally antagonized by mycotoxins. MT has proven to be affected by micro-fungi of the Fusarium and Alternaria genera, in particular, and their mycotoxins. Alternariol-methyl-ether (AME), alternariol (AOH), beauvericin (BEA), deoxynivalenol (DON), enniatin A (ENNA), enniatin A1 (ENNA1), enniatin B (ENNB), enniatin B1 (ENNB1), HT-2 toxin (HT-2), T-2 toxin (T-2), tentoxin (TEN), and zearalenone (ZEA) seem to be most significant in MT-based dietary supplements. This review focuses on summarizing cases of mycotoxins in MT to emphasize the need for strict monitoring and regulation, as mycotoxins in relation with MT-based dietary supplements are not covered by European Union legislation.