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Herbal Spotlight: Milk Thistle and Thyroid Health

Published February 24 2014

Milk thistle is one of the more popular herbs, as it is well known for its role in liver health. The active complex of milk thistle is composed of three isomer flavonolignans (silybin, silydianin, and silychristin) collectively known as silymarin (1) [1]. In this article I will discuss some of the benefits of milk thistle, and how it can benefit people with thyroid and autoimmune thyroid conditions.

Although the focus of this article is on milk thistle, in order to better understand the benefits of this herb, one should also have a greater appreciation for the role of the liver. Many people reading this already know that the liver is important for biotransformation and detoxification. We’re exposed to many different toxins through the food we eat, the water we drink, and the air we breathe. The liver is responsible for converting these substances into less toxic compounds, and also aids in the excretion of these compounds.

But in addition to helping with biotransformation and detoxification, the liver also plays an important role in the metabolism of carbohydrates, fats, and proteins. It also stores certain vitamins, and plays a role in vitamin D synthesis. The liver also plays a role in blood coagulation.

What Are Some Of The Benefits Of Using Milk Thistle (Silymarin)?

Benefit #1: Has antioxidant activity and inhibits the binding of toxins. Silymarin acts as an antioxidant by reducing free radical production and lipid peroxidation, has antifibrotic activity, and inhibits binding of toxins to the cell membrane receptors of the liver cells (2) [1]. With regards to it being an antioxidant, the evidence shows that silymarin offers a substantial protective effect and has a free radical scavenging mechanism against exogenous hydrogen peroxide-induced oxidative stress damages, and therefore can be used for protection against toxicity induced by environmental contaminants. And so this is why many people take milk thistle as a preventative measure against environmental toxins (3) [2].

Benefit #2: Can prevent or reduce the severity of liver damage. There is plenty of evidence which shows that milk thistle can help with liver damage. Liver cirrhosis, non-alcoholic fatty liver and steatohepatitis are risk factors for hepatocellular carcinoma, and insulin resistance and oxidative stress are the major mechanisms leading to injury of the liver cells in these patients (4) [3]. Silymarin exerts membrane-stabilizing and antioxidant activity, it helps to regenerate liver cells ; furthermore it reduces the inflammatory reaction, and inhibits the fibrogenesis in the liver (4) [3]. Another study concluded that silymarin can be used as a supportive element in the therapy of Amanita phalloides poisoning and alcoholic liver cirrhosis (5) [4]. It’s pretty amazing that taking milk thistle not only can prevent liver damage from occurring, but can potentially regenerate liver cells as well.

Benefit #3: Can be beneficial for hepatitis. Milk thistle can potentially be effective in both chronic and acute hepatitis. I briefly spoke about milk thistle in my article “Is There A Connection Between Hepatitis C and Thyroid Health? [5]“, as I discussed how milk thistle probably is more effective in helping people with acute hepatitis C, although it still might be beneficial for people with chronic hepatitis C. Though silymarin does not have antiviral properties against the hepatitis virus, it promotes protein synthesis, helps in regenerating liver tissue, controls inflammation, enhances glucuronidation and protects against glutathione depletion (6) [6]. I’ve spoken about glutathione in previous articles and blog posts, as this is an antioxidant which plays a major role in detoxification.

How Can Milk Thistle Benefit People With Thyroid and Autoimmune Thyroid Conditions?

Milk thistle doesn’t have a direct effect on thyroid health. However, this doesn’t mean that people with thyroid and autoimmune thyroid conditions can’t benefit from taking this herb. Here are a few reasons why people with these conditions might benefit from taking milk thistle:

1) Milk thistle helps to protect the liver, which has a direct role in thyroid health. Earlier I mentioned a few of the more important functions of the liver. But with regards to thyroid health, the liver plays an important role in converting thyroxine (T4) to tri-iodothyronine (T3). The liver also plays a role in the deactivation of thyroid hormone, along with the transport of thyroid hormone. As a result, problems with the liver are likely to lead to problems with thyroid health.

2) Antithyroid medication such as Methimazole and PTU can damage the liver (7) [7] (8) [8] (9) [8] (10) [9]. Although having a hyperthyroid condition alone can sometimes raise the liver enzymes, the odds of this happening are greatly increased when someone is taking antithyroid medication. And the reason for the elevated liver enzymes is because liver damage is occurring. This doesn’t mean that people with hyperthyroidism and Graves’ Disease should avoid taking antithyroid medication. Although I personally chose to take Bugleweed, the truth is that for some people, taking an herb such as Bugleweed might not be potent enough to manage the hyperthyroid symptoms. The same can be true with L-carnitine, which also has antithyroid activity when taken in high doses. While herbs and supplements can be a great substitute for the prescription drugs, some people do need to take antithyroid medication.

As a result, many of my patients take antithyroid medication while following a natural treatment protocol. They are of course taking the medication to control the symptoms while we address the underlying cause of the condition. But it’s a good idea to monitor the liver enzymes every now and then while on the antithyroid medication. Many people do fine taking the medication and don’t experience any liver damage, and thus the liver enzymes are normal. But even if this is the case, taking milk thistle each day might be a good idea until the thyroid hormone levels are back within a normal range.

3) Everyone is exposed to many different toxins. The truth is, we’re bombarded by toxins. And although we can do things to minimize our exposure to these toxins, it is impossible to completely avoid them. This is one of the reasons why I personally follow a 21-day liver detoxification program a few times per year. And quite frankly, while this might sound extreme to some people, in this day and age it might not be enough, as it probably is a good idea for most people to do sauna therapy on a regular basis, and it might be wise to take herbs such as milk thistle on a daily basis as a preventative measure. With that being said, even though milk thistle seems to be safe when taken on a long term basis, I’d be cautious about taking any herb on a permanent basis.

Are There Contraindications With Milk Thistle?

Most people can tolerate milk thistle well. However, milk thistle is a member of the compositae family, and those people who have a known sensitivity to other members of this family (i.e. ragweed or daisies) might react to milk thistle. According to some herbalists, milk thistle is safe during both pregnancy and lactation, although I still would be cautious when taking this herb if pregnant or breastfeeding.

In summary, milk thistle is a wonderful herb which can benefit many people, and not just those people with thyroid and autoimmune thyroid conditions. However, the liver does play an important role in thyroid health. And since milk thistle helps to protect the liver, one can argue that many people with thyroid conditions should take this herb. This is especially true for those people who have a problem converting T4 to T3 due to a possible liver malfunction. However, people with hyperthyroidism and Graves’ Disease also should consider taking milk thistle, and this is especially true when taking antithyroid medication, which has the potential to cause liver damage.