Dear Doctor: I read a terrible story about a couple who went to the Caribbean and got hookworms by going barefoot. Is that only possible in the tropics, or should I be worried here in the United States? I hate wearing shoes in the summer.

Dear Reader: Let's start with a recap of the story. A couple visiting a Caribbean resort came home with more than a tan. After a barefoot walk on the beach, their feet began to itch. They chalked it up to bug bites and, amid much scratching, continued their vacation. Once home, however, they developed large, weeping blisters on their feet, followed by subcutaneous markings that looked as though something might be burrowing beneath their skin.

It was. During that barefoot stroll, the couple had unwittingly walked through an area contaminated by hookworm larvae. Larvae are present anywhere that an infected animal (or human -- a bit more on that in a moment) has left its stool. In this case, the hookworms were a species that lives in the intestines of dogs, cats and wild animals. This was actually good news because humans are imperfect hosts for this particular parasite: In other words, the larvae can't mature or reproduce. As a result, infections typically resolve without medication in about four to six weeks. (In the couple's case, once the infection was identified by inspection of a stool sample, they were given a course of antiparasitic drugs.)

The key to understanding what happened lies in the life cycle of the hookworm. The parasite, a nematode, thrives in moist, warm areas and thus is common in the tropics and subtropics. Its eggs are deposited into the soil via the feces of an infected host. After the eggs hatch and the larvae mature, they are ready to burrow into the skin of whichever creature crosses their path.

When hookworm larvae enter their ideal host, they become a serious health threat. They complete a complex journey through the body that brings them to their final destination, the inside of the small intestine. Once there, they latch onto the intestinal walls with the hook-like mouths that give them their name, and begin to feed on the host's blood.

Two different species of hookworm can infect humans -- Necator americanus and Ancylostoma duodenale -- with the former the more prevalent. At least 575 million and up to 740 million individuals are affected by hookworm, making it one of the most common parasitic infections in the world. Without treatment, infection by these species causes severe anemia. Over time, this results in weakness, extreme fatigue, shortness of breath and irregular heartbeat. Children with hookworm infection often have stunted growth and cognitive problems, and become susceptible to other illnesses. Adults become so exhausted that they cannot function fully.

Although infection by N. americanus was once a grave public health problem in the United States, particularly in the Southeast, it is now quite rare, thanks to education and eradication programs, as well as improvements in sanitation. However, hookworms that infect pets and wildlife remain common. If a barefoot walk were to take you across soil contaminated by the feces of an animal (or human) infected with hookworm, then you could indeed be at risk.

(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: 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.)

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.

(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.)