Dear Doctor: What are the pros and cons of taking milk thistle?

Dear Reader: Let's begin with some background on this purple-flowered plant that most people in this country think of as an invasive weed. It's a member of the thistle family, so-named for the sharp projections upon the leaves and stems. Although it originated in Europe, milk thistle (Silybum marianum) has made its way to many parts of the world, including the hills of Southern California, where I've pricked my legs on it many times while hiking. Nuisance or not, however, the seeds of the plant have been used for medicinal purposes for more than 1,000 years. That's because they contain silymarin, a mixture of plant chemicals known as flavonolignans.

Milk thistle is often touted as a supplement to protect the liver. Before today's more effective treatments for hepatitis C, many patients used milk thistle in an attempt to limit liver damage from the virus. Although silymarin has been shown to have antiviral and antioxidant activity, and theoretically could limit tissue and cellular damage caused by the virus, the majority of studies of silymarin and hepatitis C have not been well-controlled.

Most notably, a 2014 review combined five randomized controlled trials of milk thistle extracts; three of the studies -- involving 216 patients -- compared changes in hepatitis C viral loads among people taking either silymarin or a placebo. The review found a slight decrease in the viral loads of people using silymarin, but it was not of statistical significance. Nor did the compiled studies find any changes in the elevation of liver enzymes, a marker of liver inflammation, in people taking silymarin.

Of course, other conditions affect the liver as well, such as alcohol liver disease and fatty liver. Research has shown some improvement with silymarin use in liver markers in both of these conditions, but the studies have been limited.

Note, however, that one of the flavonolignans, silybin, may have particular potential in limiting damage to the liver. In one study in mice, the addition of silybin prior to the exposure of toxic mushrooms decreased the chance of severe liver damage. Also, case reports have shown that the administration of silybin extract increased the survival rate among people with death cap mushroom poisoning. Further, the larger compound, silymarin itself, can decrease liver toxicity in mice given high doses of acetaminophen.

The larger compound has also been studied in people with diabetes. The thinking is that its anti-oxidant and anti-inflammatory effects could theoretically reduce complications of the disease. And, in fact, preliminary studies in people with diabetes have shown that it does have beneficial effects upon the kidneys, nerves and the retinas.

Silymarin may even have anti-cancer properties, but this needs to be studied further in humans.

As for the side effects of silymarin, they include abdominal discomfort, headache, muscle aches and fatigue. Because the compound acts within the liver, it could theoretically interact with multiple medications metabolized there. Thus far, however, studies of people taking up to 140 milligrams per day of silymarin have not shown significant drug interactions.

In summary, the components of milk thistle supplements do seem to have some beneficial effects. Future studies will need to assess its full benefits, or risks, in those with liver disease, diabetes and cancer.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: My girlfriend is all-in on one of those low-carb diets and has pretty much stopped eating vegetables. (When she does eat any carbs, it's the bread and sweets that she craves). I'm hoping one of the new studies about leafy greens and brain health might change her habits. Can you talk a bit about them?

Dear Reader: Any time you follow a restrictive diet -- and the low-carb variety certainly qualifies -- you run the risk of shorting the body of a range of nutrients essential to health and well-being. As we discussed in a recent column about the super-popular (for the moment, anyway) ketogenic diet, which takes the low-carb philosophy to extremes, using the allotted carbohydrates wisely becomes all the more crucial.

Fortunately, for your proposed plan to get your girlfriend to dig her salad bowl out of storage, the leafy greens in the studies you've referenced are low in carbohydrates and high in a range of health benefits. And according to several recent studies, they may quite literally be brain food.

Let's start with a study published last December in the journal Neurology. Researchers found that older individuals who ate at least one serving per day of leafy greens, like kale, lettuce, spinach, collard or mustard greens, fared better on tests that measure memory and thinking skills than did those who rarely or never included those vegetables in their diets.

The study looked at 960 people between the ages of 58 and 99 who were part of the Memory and Aging Project, which has been ongoing at Washington University in St. Louis since 1979. The purpose of the project, known as MAP, is to study changes in the intellectual functioning in individuals over time as they age. Over the course of five years, each person evaluated in the study had completed at least two cognitive assessments and had tracked their diets.

Those who ate a serving of leafy greens every day experienced half of the cognitive decline as did those who avoided those vegetables. According to the researchers, at the end of the five years, after adjusting for variables like age, sex, education, participation in cognitive and physical activities, smoking and alcohol consumption, the leafy green eaters were an equivalent of 11 years younger mentally than the other group. This bolsters the outcomes of previous studies, which found that the nutrients in these vegetables can put the brakes on cognitive decline.

The specific nutrients in those leafy greens that are most likely to be beneficial turn out to be vitamin K, lutein, folate (also known as folic acid) and beta-carotene. Researchers at the University of Illinois zeroed in on lutein, a carotenoid vitamin that accumulates in neural tissues. The results of their study suggest that, because lutein appears to support both structure and function in the neural membranes, it may be neuroprotective.

The results of these studies are fascinating and, thanks in part to ever-advancing imaging techniques, are opening up new avenues of study. When it comes to your girlfriend, though, we hope the findings are enough to get a salad on her plate.

Dear Doctor: My brother died from Wegener's disease at age 62. Could you please tell me more about this disease -- what causes it and what can be done? Could there be a connection to the fact that our father died of rheumatoid arthritis at age 64?

Dear Reader: I'm sorry to hear about the loss of your brother -- and understand your desire to learn more about this rare disease. For starters, Wegener's is named after Friedrich Wegener, the German pathologist who defined it. In recent years, Wegener's has been called granulomatosis with polyangiitis (GPA), which more accurately describes the disease. Granulomatosis refers to masses of scar tissue, and polyangiitis refers to inflammation of blood vessels.

An autoimmune condition that affects one to two per 100,000 people per year, GPA is usually linked to an abnormal protein called ANCA, for antineutrophil cytoplasmic antibody. ANCA attacks two types of white blood cells, monocytes and -- more important -- neutrophils.

Neutrophils normally help fight infections by ingesting and killing bacteria. They also help in the inflammatory response to injury. ANCA, however, causes the neutrophils to inflame normal tissue. It also causes them to release chemicals normally reserved for killing bacteria, causing even greater destruction to normal tissue. This dual assault affects the smaller blood vessels of the body, especially in the respiratory system and in the kidneys; symptoms can progress either slowly (over several months) or rapidly (over a matter of days).

The hallmark of the disease is vascular inflammation of the organs, most notably the lungs, affecting their air spaces and leading to scar tissue that forms nodules within them. In a severe form of GPA, the small blood vessels leak blood into the air spaces, causing a sudden drop in a person's oxygen level. This is turn leads to a coughing-up of blood and the failure of the respiratory system.

In most cases -- 90 percent -- GPA also affects the sinuses, nose, ears, mouth or throat. These symptoms can appear similar to those caused by common nasal congestion, sinusitis or a runny nose. But as the disease progresses, it can cause ulcers in the nose and mouth, hearing loss and the destruction of nose cartilage, resulting in nasal deformities.

The kidneys don't escape attack either. Because blood is filtered by the small vessels of the kidneys, inflammation of these blood vessels compromises the kidneys' filtering mechanism. Early damage can be diagnosed through tests that detect protein in the urine, but ultimately about 80 percent of people with GPA will develop severe kidney problems within two years of diagnosis -- and many will have kidney failure.

GPA can also damage the eyes, the skin and the nervous system.

Because the disease is, in effect, an autoimmune attack, treatment focuses on suppressing the immune system with steroids and other drugs. Although these drugs have side effects, they're effective in controlling the disease. Once remission occurs, patients can switch to milder immune-suppressing drugs. Note that the disease can reoccur, however, sometimes induced by infection.

Why the disease develops is unknown. It's possible that an infection may lead to the formation of ANCA, causing GPA; genetic factors may play a role as well. In fact, one study found similar genetic changes in GPA and rheumatoid arthritis, so your father's history of rheumatoid arthritis may be a factor. As you can see, however, more research is needed. You're not alone in wanting answers.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)