Dear Readers: We've been reading your letters. Thank you for your interest in our thoughts, the humor with which you evaluate -- and sometimes chide -- us, and the passion you continue to show for health sciences and research. Your thoughts and questions are always interesting, often touching and never fail to make us think.

With that in mind, we're following up on some past columns that caused a stir with readers.

Toenail fungus: The column about toenail fungus remains a hot topic. As you may recall, this is a common infection that causes nails to thicken, darken and become malformed. The most effective treatment is an oral anti-fungal drug, such as Lamisil or Sporanox, which can come with side effects. Prescription topical treatments like the medicated nail polish Penlac or antifungal creams are also available. But whichever route you go, this can be a tough infection to beat.

Quite a few of you have offered two interesting home remedies, each of which has been the subject of several studies. Unfortunately, neither of these will actually cure the fungus. But the research agrees with you readers that the appearance of the affected nails can be improved, and the extent of the fungal damage lessened.

-- Topical treatment with tea tree oil: A natural (and quite strong-smelling) disinfectant, this essential oil is derived from the native Australian plant Melaleuca alternifolia. Readers recommend that you apply it to infected nails twice daily for at least eight weeks. For the fungus to be eradicated, the nail must grow out completely. That means results can take up to a year. Tea tree oil is widely available at health food stores and sometimes in the nutritional supplements section of your local drug store.

-- Topical treatment with Vicks VapoRub: The combination of camphor, eucalyptus oil and menthol, the three main ingredients in Vicks VapoRub, is believed to stop the growth of certain fungi. Follow the same application process as for tea tree oil. Numerous readers swear by this.

And for a bit of preventive hygiene, use rubbing alcohol on nail clippers between uses to prevent the risk of further infection.

Nosebleeds: In response to the column explaining the hows and whys of sudden nosebleeds, a reader shared a tip for individuals whose homes are heated with forced air, or who live in arid environments. She followed her physician's advice to put a dab of K-Y Jelly into each nostril at bedtime (not Vaseline, which is petroleum-based), and the nosebleeds that had plagued her stopped.

Copper pans: A reader considering the purchase of a set of unlined copper pans wondered if they pose a health risk. The answer is: It depends on what they're used for.

Copper is easily dissolved by acidic foods like tomatoes or tomato sauce, which should never be cooked or stored in copper. While small amounts of copper are considered safe, when ingested in large amounts it can cause nausea, vomiting and diarrhea.

If you do use unlined copper pots and pans, research the acidity of the foods you plan to cook in them. Or buy a couple of pretty ones and use them for decor.

(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 benefits and risks of taking kava?

Dear Reader: The kava shrub originates from the South Pacific, where Pacific Islanders used it to promote psychological and physical relaxation for medicinal and ceremonial purposes. Within traditional cultures, the root of the plant is crushed, ground and then combined with a mixture of water and coconut milk to make it drinkable. In the naturopathic boom of the 1990s, kava was touted as a safe alternative to other medications used for anxiety. Today, kava is a popular supplement for anxiety, and various brands can be found in any health food store.

The root of the kava plant contains 18 different phytochemicals, or plant-based compounds, known as kavalactones. These compounds alter the conduction of nerve signals, decrease excitatory neurotransmitters, increase the ability of the amino acid GABA to bind its receptors, inhibit the enzyme monoamine oxidase, and reduce uptake of the neurotransmitters noradrenaline and dopamine. All of this is a technical way of saying: Kava can help reduce anxiety.

A 2003 review of 11 randomized controlled trials with a total of 645 patients assessed kava supplements' ability to treat anxiety. The studies used varying levels of the kavalactones, from 60 to 280 milligrams. These doses are significantly higher than what Pacific Islanders traditionally used. The studies varied from one to 25 weeks.

Ten of the 11 studies showed a decrease in anxiety compared with placebo. These benefits appeared to be comparable to the effect of tranquilizers such as benzodiazepines and the anxiety drug buspirone. Side effects included nausea, stomach aches, drowsiness and headaches. No liver toxicity was reported, but then, no liver tests were performed.

Note that kava has been banned in the United Kingdom and within Europe due to liver toxicity. More than 100 cases of liver toxicity related to the use of kava have been identified, some leading to liver transplant and others leading to death. There are many reasons for liver damage. For one, kava depletes glutathione, a chief antioxidant, within the liver. It also inhibits enzymes involved in the metabolism of many drugs. Many of the cases of liver toxicity were seen in people who had prior liver disease or used alcohol in addition to kava.

You may think kava is safe if you don't have liver disease or are not taking medications metabolized by the liver, but that might not be the case. A study of 31 people in Hawaii who were regular kava drinkers showed a significantly greater elevation of two liver enzymes compared with people who were not kava drinkers. There is some evidence that kava that is prepared with water is less harmful to the liver than suspensions prepared in acetone or ethanol.

Studies have shown that consumption of kava supplements leads to a slower reaction time and an impairment of motor skills. However, there has been no proof of any decline in cognitive function. Also, because it inhibits multiple enzymes and has psychoactive properties, kava likely should not be taken with anti-depressants.

In summary, kava may help relieve anxiety in the short term. However, due to the severe side effects at its current doses, I would be hesitant to use it for the short term and recommend not using it in the long-term. Cognitive behavioral therapy has greater long-lasting benefits.

(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: Our family visits a lake in the mountains every summer where the water almost never gets above 60 degrees. I dislike swimming in cold water, but my husband and dad insist that it's good for you. It won't get me into the water, but I just want to know -- are they right?

Dear Reader: Some people find cold-water swimming invigorating. Others, like the groups who take part in those midwinter "polar bear plunges," love an even icier challenge. And then there are those of us who prefer not to suffer for our swim.

Swimming in and of itself is great exercise. Your heart, lungs and muscles all get a workout. The buoyancy of the water is kind to weight-bearing joints, and the concentration, isolation and repetition of swimming laps can be meditative. And while there are plenty of theories about how and why spending time in cold water is good for you -- it sure does feel fantastic once you get out -- when it comes to scientific evidence, things get a bit trickier.

Research into cold-water immersion tends to focus on its use as therapy for sports injuries. Some studies with individuals who do open-water ocean swimming cite a lower rate of respiratory illness, but that data is anecdotal. And while several studies have found an increase in white blood cells in individuals who take daily cold showers, whether the resulting boost in immune response translates into long-term better health remains an open question.

What's more apparent are the potential dangers of swimming in cold water. Water conducts heat far more efficiently than air. By some estimates, you lose heat 25 times more quickly in water than in air. That's why the body responds so differently to a walk in 60-degree weather and a swim in water at that same temperature. It's also why, when you get into water that's 60 degrees or colder, it causes a phenomenon known as "cold shock."

In cold shock, the body releases adrenaline and stress hormones, which can make you either feel exhilarated or panicky. In response to the sudden cold, you lose control of your breath. Your lungs contract and you gasp and breathe irregularly, a response that can last for up to a minute. To protect the vital organs, blood vessels contract, which raises blood pressure. As the body redirects blood flow away from the periphery and to your core, coordination can become impaired.

Because of this, experienced cold-water swimmers warn against jumping into icy water. Instead, they recommend that you dash water on your face, chest and shoulders to "warn" your nervous system of what's coming. Then wade in, steadily but slowly, until you're fully submerged. Monitor your breathing and heartbeat and, if all is well, off you go.

It's understandable that your dad and husband would want to make swimming an all-family affair. But whether to brave the chilly lake is a matter of personal preference.

If you -- or they -- have high blood pressure or any heart issues, don't do it. And if you are going to go the cold-water route (for just a few minutes or so the body will acclimate), have fun.

Just don't stay out too long. And never swim alone.

(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.)