Research suggests herb can influence blood sugar control, iron chelation and more.

By Kerry Bone, BSc (hons), Dipl. Phyto.

Most of us know about the impressive research on milk thistle (Silybum marianum) and the liver. This herb, and more specifically a concentrated extract from it known as silymarin, has been shown in many lab experiments and clinical trials to protect the liver from toxic attack.¹ This has led to its clinical uses for liver damage or disease, including abnormal liver function tests, toxic mushroom poisoning, fatty liver and even (more controversially) hepatitis.¹

To my surprise, I discovered that the health benefits of milk thistle don't just stop there. New research is showing a beneficial role in the management of a diverse range of conditions, including type 2 diabetes and excess iron in the body. It can even enhance milk production.

Type 2 Diabetes

The benefit of milk thistle for type 2 diabetes is an exciting development. This lifestyle-related condition, characterized mainly by a relative lack of activity for insulin known as insulin resistance, has reached epidemic proportions in Western countries. There were some promising signs from early research that silymarin might help diabetes, but only in the past few years has solid evidence emerged.¹

In a trial published in 2006, treatment with silymarin at 200 mg three times a day dramatically improved blood sugar control.² After four months, average fasting blood glucose level fell by 15 percent in the group taking the silymarin, whereas it rose by 13 percent in the placebo group. Type 2 diabetes is a progressive condition, so in long-term studies such as this, we often see the placebo group get worse. In other words, there is a negative placebo effect. Glycated hemoglobin, which is the best measure of long-term blood sugar control, fell from 7.8 percent to 6.8 percent in the silymarin group, whereas it rose from 8.3 percent to 9.5 percent in the placebo group. In other words, the silymarin treatment resulted in well-controlled diabetes, whereas the diabetics in the placebo group were poorly controlled.

The benefits did not just end at better blood sugar levels. Type 2 diabetes is characterized by abnormal levels of fats in the blood, especially triglycerides. Milk thistle treatment lowered triglyceride levels by 25 percent, but for the placebo, they rose by 12 percent. Cholesterol also went down by around 10 percent in the group receiving the herb.

Another study supports the use of milk thistle for type 2 diabetes. This trial assessed the effect of adding the herb to patients with long-standing diabetes who were poorly controlled by their diet and the drug glibenclamide.³ The placebo-controlled clinical trial lasted over four months and the dose of silymarin was 200 mg/day.

Average fasting blood glucose fell by 20 percent in the herbal group and glycated hemoglobin fell by 16 percent. Changes in the placebo group were negligible. In addition and quite surprisingly, the silymarin patients lost weight. Body mass index (BMI) values fell significantly by 9 percent. In other words, the milk thistle appeared to cause an average weight loss of around 18 lbs. The spike in blood glucose that occurs within four hours of a meal was flattened by a considerable 37 percent by the silymarin treatment, against a significant 19 percent rise in the placebo group.

Why does milk thistle help reduce insulin resistance and provide benefits in type 2 diabetes? The authors of the study suggest it could be related in some way to the antioxidant properties of the herb. It may also be due to the effect of silymarin in inhibiting a key cell-signalling chemical known as protein kinase C (PKC) that is abnormally raised when insulin resistance has developed.

Iron Chelation

It has also been discovered that milk thistle has an activity toward iron in the body. A few years ago, a group of scientists found that silybin, one of the plant chemicals found in milk thistle and the silymarin extract, had a strong chelating capacity for iron.⁴ The authors suggested that the herb could be used for iron overload disorders and high ferritin levels (an indicator of iron stores). The toxicity of the silymarin is low compared to the iron-binding drugs.

Since then, I have seen good results in using silymarin at 200 mg three times a day to reduce elevated ferritin or help control the genetic iron overload disorder hemochromatosis. It is good to see this hunch confirmed in a clinical trial. In an open-label trial design, silybin (complexed with phosphatidylcholine [lecithin] to help its bioavailability) significantly reduced serum ferritin by around 15 percent over four weeks in patients with chronic hepatitis C.⁵ There was no significant change in serum iron or transferrin saturation. However, given this capacity of the actives in milk thistle to bind iron, it is best taken away from meals and iron supplements if iron status is low.

Milk Production

One surprising new role for milk thistle is the enhancement of milk production in healthy breast-feeding mothers, verified by a clinical trial. Following an agricultural trial demonstrating that silymarin promoted milk production in dairy cows, a group of scientists investigated its value in humans.⁶ The trial enrolled 50 healthy lactating women who received a daily dose of 420 mg of micronized (very fine) silymarin or an identical placebo for 63 days.

At both days 30 and 63, there was a clear and significant difference over placebo in favor of the silymarin group in terms of total milk production (p<0.01). There also appeared to be a cumulative treatment effect, with a 64.4 percent increase above baseline at day 30 for the silymarin group (versus 22.5 percent for placebo) which increased to 86.0 percent by day 63 (versus 32.1 percent for placebo). Analysis of the biochemical parameters (water, fats, carbohydrates and proteins) of the milk confirmed no difference between the active and placebo groups. Testing of the milk from a smaller group of women who received 1,800 mg/day silymarin for five days found no detectable levels of silymarin flavanolignans.

Given the common name of milk thistle, why is it surprising to learn of its galactagogue effects? The answer is that the most likely source of this common name is the appearance of the plant, not any traditional galactagogue usage. Specifically, the white stripes on the leaves were said to represent the milk of the Virgin Mary.^7,8 There is no reference to any galactagogue action in texts reflecting traditional use.⁹ Perhaps this confusion serendipitously led to its discovery, or maybe this is a previously unrecognized example of the doctrine of signatures (in which the appearance of an herb suggests its therapeutic activity).

Kerry Bone is a practicing herbalist; co-founder and head of research and development at MediHerb; and principal of the Australian College of Phytotherapy. He also is the author of several books on herbs and herbal therapy, including Principles and Practice of Phytotherapy and The Essential Guide to Herbal Safety.