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What Is Milk Thistle? Its Benefits for Liver and Beyond

Milk thistle is a medicinal herb subject of many studies for its health benefits. Primarily utilized for health issues concerning the liver and gallbladder, due to its antioxidant properties, milk thistle has also been found to have the potential to help with blood sugar regulation, inflammation, and increased oxidative stress. However, studies have shown inconsistencies, so more research is needed to confirm these benefits.

What is milk thistle?

The seeds and fruit of milk thistle, or Silybum marianum, have been used for more than 2,000 years as botanical therapy; however, its use as an herbal remedy in our Western world has only been approved by the U.S. Food and Drug Administration as “Generally Regarded as Safe” since 2001.

Derived from a prickly plant, the bioactive ingredients in milk thistle are compounds known as silymarin, a group of different flavonoids. It originated from the Mediterranean region, but over time, it has spread across South America, Africa, Australia, Asia, and the eastern United States such as California.

As a flavonoid, milk thistle is predominantly known for its antioxidative and protective power against liver diseases, such as cirrhosis and hepatitis C. However, some data supports its potential to improve issues, such as gallbladder disorders, diabetes management, metabolic disorders, and inflammation.

Potential milk thistle benefits

Due to its antioxidant and anti-inflammatory properties, this herbal supplement has been found to have a wide range of benefits. Beyond liver protection and antioxidant effects against various diseases, milk thistle has also been used for centuries to help regulate the immune system and protect the liver from snake bites, alcohol, and other environmental toxins. But is there enough scientific evidence to prove these benefits? Here are seven benefits of milk thistle with some supporting studies:

1. May improve liver health

Liver diseases are a growing concern in the U.S., with chronic liver disease or cirrhosis being considered the 12th leading cause of death in 2020, according to the American Liver Foundation.

One meta-analysis found that in a population of non-alcoholic fatty liver disease (NAFLD) patients, silymarin, the bioactive compound in milk thistle, seemed effective in reducing the levels of transaminase, an enzyme the body releases upon detecting damaged or injured liver cells. These benefits may have been attributable to milk thistle’s possible anti-inflammatory and antioxidant activity.

Other research that investigated the impact of milk thistle on patients with hepatitis C found no evidence of it being beneficial.

However, more research is needed to confirm efficacy. A systematic review with meta-analysis found that most studies concerning the link between liver health benefits and milk thistle were of low quality, showing inconsistencies and lacking statistical significance.

2. May help with type 2 diabetes

A systemic review and meta-analysis indicated that milk thistle, when combined with traditional diabetes treatments, may improve fasting blood sugar levels in patients with type 2 diabetes. However, researchers pointed out that the studies included were of low quality, so these didn’t provide adequate evidence required to confirm the herb’s effectiveness on type 2 diabetes.

3. May improve insulin resistance

Insulin resistance is linked to many liver diseases and is also a condition that often precedes the development of type 2 diabetes. Additionally, insulin resistance is also closely related to being overweight or obese.

There’s conflicting evidence on milk thistle’s impact on insulin resistance. Several studies in animal models have reported silymarin to have a positive impact on glucose or carbohydrate metabolism and insulin resistance. However, a comprehensive review of research published in 2021 also noted a mice study where silymarin was found to induce and enhance insulin resistance.

Such mixed results prompt additional research, especially in human subjects.

4. May help cancer treatment efficacy

Silymarin and silibinin have been studied for their potential benefits as complementary therapy in various types of cancer, including breast, ovarian, lung, skin, prostate, cervical, bladder, liver, and colon cancer.

Research in animal models has shown that milk thistle interferes with certain harmful cell-signaling pathways that normally allow cancer cells to grow and multiply and may also activate certain genes that suppress tumors and regulate tumor cell growth.

Additional studies have also shown promise in milk thistle making cancer cells more sensitive to chemotherapy by reducing drug resistance, potentially increasing the effectiveness of cancer drugs.

Current research shows weak evidence, so more studies are needed to translate these results over to potential outcomes in humans as these were all done in cell cultures or animal models.

5. May help reduce allergic asthma symptoms

Allergic asthma often manifests in wheezing, coughing, and difficulty breathing as a reaction to a chronic inflammation of the airways. Compounds in silymarin have been reported to help reduce the severity of these symptoms by reducing inflammation and oxidative stress in the lungs and modulating the immune responses.

6. May improve skin health

Researchers have evaluated milk thistle’s impact on acne by comparing its efficacy in combination with the treatment of doxycycline against doxycycline alone. While milk thistle on its own wasn’t as efficacious as doxycycline therapy, findings have shown slightly improved outcomes with patients who did the combined treatment. The research available for this benefit is very limited.

7. May protect brain health

Research suggests that silymarin may promote the growth of new neurons and protect existing ones from inflammation and oxidative stress. This neuroprotective effect may help prevent the cognitive decline associated with aging and neurodegenerative diseases (diseases that are caused due to loss of neurons).

One study on mice with induced Alzheimer’s disease showed that milk thistle treatment significantly improved cognitive abnormalities, particularly memory impairment, and reduced oxidative damage.

With the reduction of oxidative damage in the brain as well as an increase in glutathione levels (the body’s master antioxidant), milk thistle has been found to protect the hippocampus — an area of the brain important for memory — that’s impaired due to neurodegeneration.

Studies have been performed in a lab setting or on mice, so more research is needed to fully uncover the potential cognitive benefits of milk thistle.

Is milk thistle safe?

Milk thistle is considered generally safe, even at a dosage as high as 700 mg taken three times per day. While it’s been found to be well-tolerated across various populations, it may cause allergic reactions, especially in people who may already be allergic to similar plants like ragweed, chrysanthemum, marigold, and daisy.

Additional side effects may include:

  • Diarrhea
  • Constipation
  • Nausea
  • Vomiting
  • Bloating
  • Headache
  • Itchiness

Due to its potential to lower blood sugar levels, people with diabetes should talk to their healthcare provider before taking it to avoid any harmful effects.

Currently, there's no clear information about the safety of using milk thistle during pregnancy or while breastfeeding. Therefore, it's generally advised against taking milk thistle supplements if you are pregnant or nursing.

The information on how milk thistle interacts with other drugs or supplements is still limited. While it doesn't significantly affect a key group of enzymes that help process drugs in the body, it does interact with certain cell transporters. This interaction could alter how other drugs or supplements are absorbed and processed, potentially leading to adverse effects, especially in people taking medications that require precise dosage management.

How to take milk thistle

Milk thistle is available in a few different forms:

  • Capsule
  • Tablets
  • Liquid extracts
  • Tea

With different types of oral formulations, the guidance from the manufacturer should be followed. It is important to consider that research has shown milk thistle to have a low bioavailability, meaning very little of its active ingredient gets absorbed into the body. Only 20–50% of oral silymarin is absorbed in the gastrointestinal tract.

Research points to a possible workaround by encapsulating silymarin in a phytosome. In this process, the phytosome acts like an envelope, with silymarin inside. It effectively carries the polyphenol through the intestinal cells and into the bloodstream, which increases its absorption and therapeutic potential.

When consuming it as a tea, soak a milk thistle tea bag in hot water for about three to five minutes on its own or in combination with another herbal tea. Keep in mind that its efficacy as a tea may be lower than all the other forms of supplementation.

How much milk thistle should you take?

The recommended dosage of milk thistle varies based on the health issue treated. Research shows silymarin to be safe in maximum doses of up to 700 mg three times a day. Otherwise, 140 mg three times per day as a general dose for adults has been studied in liver cirrhosis and other conditions. There is no specific dose of silymarin for any particular condition. It is important to follow the dosage guidelines of each product and speak to your healthcare provider for personalized recommendations.

Choosing a quality milk thistle supplement

Choosing the right milk thistle supplement can make the difference between seeing a positive impact and seeing no impact at all. Whether you prefer capsules, tablets, liquid extracts, or tea, ingredient quality, manufacturing standards, brand reputation, and appropriate certifications are all important factors to consider before adding a supplement to your cart. Here are some other factors you may want to consider before purchasing milk thistle supplements:

  • Appropriate ingredients. Confirm the silymarin content, the active ingredient in milk thistle. Quality supplements typically contain 70–80% silymarin. Supplements that utilize phytosomes may provide enhanced absorption of silymarin and may often be more effective. Choose a form that best suits your dietary needs.
  • Third-party validation. Certifications by third-party organizations such as USP (United States Pharmacopeia), NSF International, or ConsumerLab guarantee that the product meets strict standards for strength, purity, and safety.
  • Transparency. Ensure that the supplement provides a clear list of ingredients, including the presence of any fillers or artificial components. The best products are transparent about their contents and free from unnecessary additives. Stay away from proprietary blends that don’t note the exact list of ingredients and the dosage of each in the supplement.

Manufacturing practices and brand reputation may also be important factors to consider:

  • Manufacturing practices. If the supplement is produced in facilities adhering to GMP (Good Manufacturing Practices), it indicates that the manufacturing process is subject to strict quality controls.
  • Brand reputation. Choosing brands with a solid reputation and customer satisfaction may point you to more reliable products. Look for online reviews and seek recommendations from healthcare professionals to gauge the effectiveness and reliability of the brand.
  • Choose organic. Check for organic certification to avoid products contaminated with pesticides or herbicides. Be mindful of the supplement's cost relative to its quality. While the cheapest option might be tempting, it often does not guarantee the same quality and efficacy as more reasonably priced, well-certified products.

Should you take milk thistle?

Milk thistle’s active compound, silymarin, has been studied for many health benefits. While it’s best known for protecting the liver, it also shows promise in improving blood sugar control, reducing inflammation, and possibly helping with other health issues such as asthma or skin issues. However, current research is limited and has often been low-quality or only done in a laboratory setting or on animal models.

More human clinical trials are needed to fully understand how it may help with various medical conditions. Side effects are mild and rare, but it’s not recommended for pregnant or breastfeeding women. Additionally, it may interact with other medications, so remember to consult with a healthcare provider before taking milk thistle, especially if you have pre-existing health conditions or are taking other medications.

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