Health 'Facts' You Only Thought You Knew

July 22, 2008

By JANE E. BRODY
In 45 years of writing about medicine and health, I’ve heard more than my share of myths and misinformation, from the merely nonsensical to the downright dangerous. And until I explored the evidence, I too occasionally fell for a “fact” that turned out to be less than met the eye.

Lately a number of medical writers have taken on these commonplaces and old wives’ tales.

Last year, Anahad O’Connor, who does so every week in his “Really?” column for Science Times, published “Never Shower in a Thunderstorm: Surprising Facts and Misleading Myths About Our Health and the World We Live In” (Times Books).

Now, Dr. Nancy L. Snyderman, a surgical oncologist at the University of Pennsylvania and a medical correspondent for NBC News, has a new book, “Medical Myths That Can Kill You — And the 101 Truths That Will Save, Extend, and Improve Your Life” (Crown).

The following myths owe something to both authors, and also to my own research. How well informed are you?

DRINK EIGHT GLASSES OF WATER A DAY I had long believed that eight glasses of plain water or caffeine-free beverages a day were important to keep the body hydrated and to prevent constipation. Perhaps the toilet paper manufacturers were behind this notion. Researchers have been unable to find scientific support for it.

The Institute of Medicine recently noted that you can meet your body’s need for liquids in many ways, including drinking coffee and tea (with or without caffeine) and eating fruits and vegetables with a high water content. Two clues that you may need to drink more are thirst and the color of your urine, which should be clear like, well, water.

If you are physically very active, especially in hot weather, repeatedly sipping cold water is helpful. But beyond two quarts, you may need to also replace the salts lost in sweat — for example, by drinking a diluted sports drink or eating foods with salt and potassium.

POISON IVY IS CONTAGIOUS The rash of poison ivy cannot be spread from person to person or even to another part of the body unless the plant’s resin is still on your hands or clothes. The rash, a contact dermatitis, may seem to spread because it often develops sequentially, depending on when and where the skin was exposed. Scratching does not spread the rash but can prolong it and cause an infection.

Over-the-counter anti-itch lotions and creams are not helpful, and those containing an antihistamine, like Benadryl, may complicate matters by causing an allergic reaction. The rash is best treated with a steroid, topically with hydrocortisone or, in more severe cases, orally with prednisone. Apply a cool wet wash cloth to oozing blisters to speed drying.

Mango skin contains a less potent form of urushiol, the allergen in poison ivy, and you can develop a rash around the mouth if you eat the flesh off the rind.

Those who think they are immune to poison ivy should know that sensitivity develops through repeated exposure.

USE COTTON SWABS TO CLEAN YOUR EARS Bellybuttons, perhaps, but not ears. My son wishes he had known this years ago, before his 2-year-old son copied his dad and punctured his eardrum with a Q-tip. The hole was so big it needed surgical repair.

Dr. Snyderman points out that a cotton swab can push wax farther into the ear, causing impaction and diminished hearing. I’ve long supported the medical adage: Put nothing smaller than an elbow in your ear. If accumulated wax is a problem, try ear wax softening drops or have your ears professionally cleaned now and then.

DON’T SWIM AFTER EATING My parents repeatedly warned us to wait an hour after a meal. It might have been good advice if I was planning to race, swim a long distance or battle a stiff current. Strenuous exercise on a full stomach is never a good idea, because it can result in stomach or muscle cramps. But experts find no harm in a gentle plunge or casual play in the water (pool or ocean) soon after eating.

What can be hazardous is swimming after drinking alcohol, because it can impair judgment and encourage undue risk-taking.

SHAVING MAKES HAIR GROW BACK FASTER AND COARSER This myth persists even though a study conducted 80 years ago disproved it. Hair that is shaved is dead, and shaving has no effect on the speed of regrowth, which comes from the living hair follicles below the skin’s surface. The new growth may appear darker since it hasn’t been exposed to the sun or chemicals for very long. Also, it may seem coarser since the ends have not been tapered by wear and tear.

COLON CLEANSING WASHES OUT POISONS Colonics, as the practice is called, has no known medical value and risks damage to the rectum or bowel. The bowel is not “dirty” and, unless disease or medication interfere, nature does a fine job of clearing out wastes. If you are concerned about unwholesome substances in your body, drink lots of water to help your body get rid of them.

NATURAL IS SAFER THAN MAN-MADE A woman recently asked me if it was safe to take “bioidentical hormone replacements.” These, I’m afraid, are estrogens, and there is no reliable evidence to support claims that they are safer than the ones made by chemists that have been linked to an increased risk of cancer and heart disease.

Remember, nature has produced some of the most dangerous substances known, including arsenic and botulinum toxin. And chemists have produced medications that can control or cure many life-threatening ills. Many important medications are derived from natural substances that not only have druglike actions but also druglike side effects.

Only carefully controlled clinical trials can assure the safety of a natural or man-made drug, and few natural substances have been tested in this way.

TAKE PAINKILLERS ONLY FOR SERIOUS PAIN In a doctor’s waiting room the other day, a woman sat groaning for an hour and a half before she finally asked the nurse for an over-the-counter pain pill to relieve her headache. Although many people see pills as the answer to every ill, others avoid medications at all costs, much to their disadvantage.

Pain medication works best if taken at the first hint of pain, and may not work well at all if you wait too long. Dr. Snyderman says to consider taking it before engaging in an activity, like heavy-duty gardening or chopping wood, that is likely to cause pain later. Before I had my arthritic knees replaced, I downed two ibuprofen tablets before every tennis match.