What precautions should parents take for children who swim a lot, particularly those on swim teams? Is there a higher incidence of chlorine-related health problems among swimmers? Does sunblock prevent the skin from absorbing chlorine?

Chlorine used to disinfect swimming pools is widely recognized as a health hazard. New research suggests that children who swim frequently in chlorinated pools may have increased risks of developing allergies or asthma. Among adults exposure to chlorine in swimming pools has been linked with other health problems including bladder and rectal cancer and, possibly, an increased risk for coronary heart disease.

The latest on this comes from a study in Belgium, which found that teens who spent more than 1,000 hours swimming in chlorinated pools had more than eight times the risk of developing asthma or allergies, compared to kids who usually swam in pools using a copper-silver disinfecting method.

A total of 847 youngsters between 13 and 18 took part in the study - 114 of them mainly swam in pools disinfected with a copper-silver ion system. The number of kids who developed asthma increased in proportion to their exposure to chlorinated pools. Those who swam for 100 to 500 hours had almost twice the risk of developing asthma; while those who spent 500 to 1,000 hours had just over twice the risk; and asthma cases nearly quadrupled among those who spent more than 1,000 hours in chlorinated pools compared to teens who swam in non-chlorinated ones.

The Belgian researchers also found that the risks of hay fever and other allergies more than doubled with significant exposure to chlorinated pools. The study was published in the online issue of Pediatrics on Sept. 14, 2009.

Another Belgian study, published in 2003, showed that an irritant released when chlorinated water reacts with urine, sweat or other organic matter from swimmers increased the risk of asthma among children who regularly swam in public pools. This irritant, trichloramine, is believed to damage the cellular barrier that protects the lungs. Blood samples showed elevated trichloramine levels even among individuals who sat at the side of pools but didn't swim.

I've long believed that inhaling chlorine fumes that accumulate above and around pools is unhealthy. Chlorine is a strong oxidizing agent and irritant, harmful to eyes and skin, the respiratory passages and lungs.

To protect yourself in chlorinated pools, consider wearing a mask and snorkel to shield your eyes, and after swimming, leave the pool area and inhale fresh air to flush the gas out of your system. Shower quickly and thoroughly to wash the chlorine off your skin.

Sunblock won't protect against the effects of chlorine. Instead, lobby local officials and public pool managers to switch from chlorine to safer, more modern disinfection methods. I use a Sigma System silver-copper ion generator in my own pool. Chlorine-based disinfection of swimming pools is obsolete.

Andrew Weil, M.D.

I know you've written before about potential health risks from cell phone use. I recently heard a report that sounds truly alarming about the cancer risk as well as other dangers. Is there new evidence?

• An analysis of 25 earlier studies by two research groups showing a 50 to 90 percent increase in the risk of glioma, a usually malignant brain tumor on the side of the head favored for cell phone use in individuals who had used cell phones for more than 10 years, and a 60 percent increase in acoustic neuromas, benign but troublesome tumors of a cranial nerve among long-term cell phone users
• A 50 to 60 percent increased risk of salivary gland tumors among people who used cell phones frequently.
• A 10 to 20 percent increased risk of hospitalization for migraine and vertigo among long-term cell phone users.
• An 80 percent increased risk for emotional and hyperactivity problems among young children who use cell phones and whose mothers used cell phones during pregnancy.

All of this sounds very alarming - and it isn't good news - but it is important to keep some of these numbers in perspective. When speaking in terms of a percentage increase in risk, bear in mind that if, for example, one person out of 100 is normally at risk of a brain tumor, a 100 percent increase in risk means that 2 people out of 100 would be at risk. It does NOT mean that as a cell phone user, you have a 100 percent chance of developing a brain tumor.

The EWG report maintains that current U.S. government radiation standards are outdated. It noted that in 2008, the European Parliament passed a resolution urging member countries to develop lower radiation limits for cell phones; no such steps have been taken in the U.S. Here, particular concern is focused on the amount of radiation that could penetrate a child's softer, thinner skull (roughly twice the amount that could penetrate an adult skull) and that long-term cell phone use starting in childhood could pose even bigger risks than those already documented. Experts in the U.S. and Europe have advised limiting youngsters' cell phone use.

I noted that the EWG check list for safe cell phone use is similar the safety tips I've been recommending for some time:

• Save long conversations for conventional phones.
• In your car, use a cell phone that has a remote antenna outside the vehicle.
• Always use a headset and keep the phone itself away from your body.
• Find out how much radiofrequency energy your cell phone emits. (This measurement is called the Specific Absorption Rate or SAR; find the SAR for your cell phone. The SAR permitted in the United States is 1.6 watts per kilogram.) The EWG also has a tool that may be easier to use to check on your phone's emissions.

To eliminate the most immediate danger of cell phone use to yourself and others, don't talk or text while driving.

Andrew Weil, M.D.

What do you think of a "soda tax" to discourage people from drinking so many calories? Is soda really the leading cause of obesity?

Sugary drinks are certainly not the only contributor to the obesity epidemic in the United States, but they are a major source of the average intake of 355 "empty" calories of sugar per day consumed in the United States. That amounts to 22 teaspoons of sugar daily. A single 12-ounce soda contains about 130 calories and the equivalent of eight teaspoons of sugar. Moreover, the high glycemic load of sugary drinks provokes insulin resistance in many people, which underlies much of the obesity in our society and raises risks of type 2 diabetes.

A tax on soda isn't a new idea, but the current proposal is more appealing to me than earlier ones. The researchers estimated that at current levels of consumption, a penny-an-ounce tax could raise $14.9 billion per year that could be directed toward health care reform. And it should decrease consumption. Evidence suggests that for every 10 percent rise in the price of soft drinks, consumption decreases by eight to 10 percent.

It's no surprise that this proposal is vehemently opposed by the beverage industry. Its representatives take issue with claims that their products are to blame for obesity and with the notion that a soda tax would remedy the problem.

In the past, I've been dubious about similar proposals, such as the so-called "fat tax" that was floated a few years ago to discourage people from buying and eating junk food including soft drinks. Ideally, this would encourage people to divert the money they spend on junk food to healthy foods.

At that time, my primary concern was that the tax might not have the intended result. But I now think that a tax on sodas is worth the experiment. We know that raising taxes on cigarettes has deterred use, especially in young people, and I like the idea of using the money raised by the tax to fund health care reform.

But, like many good ideas, I'm not so sure that a soda tax will win enough political support to become a reality.

Andrew Weil, M.D.

My granddaughter, age 10, has a very bad case of vitiligo. She is spotted from her head to her little toes. Are there any herbs that can help? 

The characteristic white patches can begin on the face, neck, armpits, elbows, hands or knees. There's no way of predicting how much of the skin will be affected. While it can be emotionally distressing, vitiligo doesn't present a threat to general health. Treatment focuses on evening out skin color, usually with steroid creams or with the drug psoralen (which reacts with ultraviolet light so that skin darkens) and ultraviolet A (PUVA) therapy. Here, you take psoralen as a pill or have it applied to affected areas, then expose the skin to ultraviolet light in the doctor's office. PUVA is said to be up to 85% effective in more than 70% of patients with vitiligo of the head, neck, upper arms, legs, and trunk. It can take months to get good results, and maintenance treatments are needed to keep the condition in check.

Some herbs do seem to help arrest vitiligo and even achieve repigmentation. One study reported in Clinical and Experimental Dermatology in May 2003 showed that ginkgo helped. I've also read that a combination of ultraviolet therapy plus the ayurvedic herb khella (Ammi visnaga) can promote repigmentation. A study of this method was reported in the May-June 2001 issue of the European Journal of Dermatology, but I don't have any personal clinical experience with it.

First, however, I suggest taking your granddaughter to a hypnotherapist. Skin conditions respond well to hypnosis; there have been reports that it can lead to repigmentation in vitiligo patients. And kids do particularly well with hypnosis.

Andrew Weil, M.D.

I've suffered with a facial headache for two years. Migraine medications don't help, physical therapy hasn't helped, decongestants don't help, and extra sleep doesn't help. My doctor doesn't know what to try next. I'm 34, female and in otherwise in good health. Do you have any recommendations?

Yet other causes include sinus problems and trigeminal neuralgia or ("tic douloureux"), a condition that causes sudden, intense facial pain most often described as "stabbing" or "lightning-like," resulting from dysfunction of the trigeminal nerve.

Your experience in trying different modalities that haven't worked is typical. Many patients with this type of pain experiment with various treatments before they find one that works for them.

Rather than recommending any particular therapy, I suggest that you consult a neurologist who specializes in headache treatment. What you need most at this time is a good diagnosis. Once you know what is causing your headaches you may be able to get appropriate treatment without further trial and error.

Andrew Weil, M.D.

What are your thoughts and opinions on a drug called MDV3100 for prostate cancer elimination in advanced-stage patients?

MDV3100 has been studied in cell cultures, where it worked well, and in mice, where it shrank tumors, but so far, it has been studied in only two human trials. The first enrolled 30 men with advanced CRPC. In 22 of the men, levels of prostate-specific antigen (PSA), a marker for tumor growth, declined with MDV3100 treatment. In 13 of those cases PSA levels fell by more than half. A second trial with 110 men tested higher doses, which reportedly were well tolerated. The company that produces MDV3100 announced in March, 2009, that it has FDA permission to launch a randomized, placebo-controlled, double-blind, multinational trial to assess overall survival with MDV3100. A total of 1,200 men with advanced CRPC will be enrolled.

If all goes well, it will be at least three to four years before MDV3100 could be ready for FDA evaluation and even longer before it becomes available for treatment.

If you're looking for ways to lower your risk of prostate cancer, here's what I recommend:

• Get regular aerobic exercise, which is associated with a reduced risk of prostate cancer.
• Take a daily multivitamin that includes antioxidants, especially selenium.
• Take at least 2,000 IU of vitamin D a day.
• Limit your intake of red meat and saturated fat, which are correlated with an increased risk for prostate cancer.
• Eat less dairy. High calcium intake from dairy products has been linked with prostate cancer. Keep your total calcium intake below 700 mg a day from all sources.
• Eat more vegetables, especially tomatoes and tomato sauce. Lycopene, a carotenoid found in tomatoes and watermelon, is associated with a lower risk of prostate cancer.
• Include whole soy foods in your diet (they contain genistein, an isoflavone that helps normalize hormone levels and seem to be linked to a lower risk of prostate cancer).
• Eat more fish: as little as one fish meal per week has been associated with a lower risk of prostate cancer.
• Eat more fiber: it helps in the normal elimination of hormones such as testosterone which influence prostate changes.
• Drink green tea: it contains EGCG, an antioxidant that kills prostate cancer cells in test tubes. Another compound in green tea blocks the actions of an enzyme that promotes prostate cancer.

Andrew Weil, M.D.

What can you tell me about bioresonance therapy? Is there any validity to a diagnosis made with this method?

The electromagnetic differences are supposedly detected by an electrical device, which is said to determine which organs are involved and be able to "cancel out" unhealthy signals. Beyond that, treatment may ;involve removing and replacing dental fillings (amalgams), which are said to carry currents that "alter the body's electromagnetic circulatory system" in undesirable ways.

No evidence supports any of these claims. In fact, the little scientific evidence that does exist refutes them. In a randomized, double-blind trial of bioresonance for treatment of atopic dermatitis in children at Alpine Children's Hospital at Davos, Switzerland, researchers found the method to be ineffective. Another trial compared the efficacy of electrodermal testing to the standard skin-prick test for allergies to house dust mites or cat dander and found no correlation between the electrodermal testing results and those from the skin-prick method. In addition, a British clinical trial to evaluate electrodermal testing for allergy diagnosis also found it to be unreliable. The findings were published in the British Medical Journal on January 20, 2001.

So far, no clinical trials have looked at bioresonance therapy for cancer, but I can tell you that there is no validity to claims that the devices can kill tumor cells by releasing "suppressed" tumor suppressor genes. In fact, the genes in question aren't suppressed at all - they have mutated and can no longer carry out their normal functions of monitoring cell division and causing defective cells to self-destruct. Once mutated, these cells can't be restored to normal activity.

In short, bioresonance therapy has no scientific validity. Avoid it.

Andrew Weil, M.D.

I have read in "The Arthritis Cure" that avocado/soybean unsaponifiables, along with glucosamine and chondroitin, are beneficial in treating arthritis. Can you tell me if the research backs up these claims, and if so, what the risks are of taking avocado/soybean unsaponifiables? 

Dr. Low Dog says that avocado/soybean unsaponifiables or ASUs, for short, are derived from the oily fractions of avocado (100 mg) and soybean (200 mg) and have an excellent safety profile and good evidence of benefit. She reports that four high-quality clinical trials have demonstrated that ASUs eased the pain and stiffness of knee and hip osteoarthritis and reduced the need for the non-steroidal anti-inflammatory drugs (NSAIDs) commonly used to treat arthritis. NSAIDs pose a risk of ulcers and gastrointestinal bleeding when taken long-term.

Dr. Low Dog further explains that the active components of the ASUs mixture have not been identified and that their mechanism of action is not well understood. However, she adds that there are no toxicity issues associated with these products. Because ;ASUs have a slow onset of action, if you want to use them, she recommends continuing to take your current pain medication for the first 4-6 weeks and then tapering off slowly. The dose of ASUs is 300-600 mg per day.

Andrew Weil, M.D.

I have been diagnosed with scombroid poisoning. I was told to take Benadryl and Zantac. I have followed this for a week. What else can I do to speed my recovery?

Symptoms usually develop immediately after eating and can include flushing, hives and itching, nausea, vomiting, diarrhea and, in severe cases, breathing problems. Treatment begins with giving antihistamine medications such as Benadryl, and, if needed, intravenous fluids to replace what you may have lost from vomiting and diarrhea. If you go to the emergency room, you may get drugs to stop the vomiting and, if needed, stronger medication to quell a severe allergic reaction. In rare cases, a breathing tube may be needed. Fortunately, the symptoms of scombroid poisoning usually subside within a few hours of treatment. If your symptoms have persisted for a week, you should be aware of another, more serious type of poisoning associated with eating fish: ciguatera (pronounced seeg-wha-terra). This can occur as a result of eating fish from warm tropical waters that have consumed ciguatoxin, a poison made in small amounts by algae and algae-like organisms called dinoflagellates. Here's what happens: little fish that eat the algae become contaminated. If larger fish eat a lot of the smaller, contaminated fish, the poison can build to a dangerous level. Because ciguatoxin is heat-stable, cooking doesn't destroy it. Fish that carry this poison include sea bass, grouper and red snapper and are most common in waters around Florida and Hawaii.

Symptoms of ciguatera poisoning typically develop two to 12 hours after eating and include nausea, vomiting, diarrhea, dizziness and numbness followed by headache, a metallic taste in your mouth, and a change in your ability to feel cold and hot - you perceive something as hot when it really is cold and vice versa. Treatment includes medication to stop the vomiting, IV fluids to replace those lost from vomiting and diarrhea, and in severe cases the drug mannitol to help reduce neurological symptoms such as dizziness, numbness and misperception of cold. Ciguatera poisoning symptoms can last from days to weeks depending on the severity of the case.

Anytime you eat bad fish in a restaurant, be sure to let the management know; your doctor should contact the local health department to make sure the fish is discarded before other people get sick.

Andrew Weil, M.D.

I heard that something in green tea could help people live longer. Is this true?

Research has shown that as cells replicate and age, telomeres get shorter and shorter and that when telomeres finally disappear, the cells can no longer replicate. Some experts have suggested that the length of telomeres may be a marker for biological aging. The shorter your telomeres, the "older" you are. Earlier studies have suggested that telomeres are highly susceptible to oxidative stress.

Now, for the Hong Kong study findings: researchers looked at telomere lengths of 976 Chinese men and 1,030 Chinese women, all over the age of 65. All the study participants completed a food frequency questionnaire.

The researchers reported that telomere length was associated only with tea drinking - participants with the highest intake, three cups per day of tea, had longer telomeres than participants who drank an average of only one quarter of a cup of tea daily. Most participants drank green tea while a few drank black tea. The investigators reported that the average difference in telomere length corresponded to "approximately a difference of five years of life" and that the "antioxidative properties of tea and its constituent nutrients may protect telomeres from oxidative damage in the normal aging process." The study was published online on August 12, 2009.

Incidentally, a recent U.S. study found that telomere length was longer in women who took multivitamins regularly. Here, researchers looked at multivitamin use in a group of 586 women between the ages of 35 and 74. They found that higher intakes of the antioxidant vitamins C and E from food were associated with longer telomere length. The findings were published in the June 2009 issue of the American Journal of Clinical Nutrition.

Andrew Weil, M.D.