Ask your doctor how much water you should drink or why you couldn't keep your eyes open after Thanksgiving dinner, and you're likely to get the same misinformation your mother-in-law might dispense. A study published in the December 2007 British Medical Journal tweaked physicians on their acceptance of some widespread medical beliefs that might now be reclassified as old wives' tales. Here's a rundown:
- Drink at least 8 glasses of water a day: The researchers who conducted the study could find no clinical evidence to support this notion. But they did dig up an article from the November 2002 American Journal of Physiology that documented the lack of evidence behind this popular recommendation. You do need to be well hydrated, but research suggests that the liquids most people drink daily - juice, milk, and decaffeinated beverages - will do the trick. Your best bets are purified water, diluted fruit juice, tea, and sparkling water flavored with fruit juice.
- We use only 10 percent of our brains: This is a real oldie that traces its history back to 1907, but didn't originate, as once believed, with Albert Einstein. Now that we know much more about neuroscience than we did 100 years ago, we can say for sure that we use much more than 10 percent of the brain, say the BMJ researchers. In fact, high-tech methods of studying the brain have not identified any inactive areas.
- Hair and fingernails continue to grow after death: This disturbing, gruesome image is pure "moonshine" according to forensic anthropologist William Maples, who was quoted in the BMJ study. However, he explained that dehydration of the body after death can cause retraction of the skin around hair and nails, giving the illusion that they have grown. All tissues require energy to sustain their functions, and no such thing is possible once the mechanism that promotes normal growth shuts down at death.
- Reading in dim light ruins your eyesight: You can get eyestrain and have difficulty focusing when trying to read in poor lighting, but these symptoms have no permanent effect on eyesight. One current theory holds that nearsightedness (myopia) might be caused by reading in dim light or holding books too close to the face. But consider this: rates of myopia are increasing and are higher now then they were centuries ago when people read by candlelight. What's more, the BMJ researchers found hundreds of expert opinions that conclude that reading in dim light doesn't permanently hurt your eyes.
- Shaving causes hair to grow back faster or coarser: No, it does not. This popular notion was disproved as early as 1928 and more recent studies have confirmed that shaving has no effect on hair growth (or regrowth), write the BMJ investigators. They speculate that when shaved hair regrows, it lacks the fine taper seen at the end of unshaven hair, making it appear coarser. And the fact that it hasn't been exposed to light may make it seem darker than other hair.
- Mobile phones are dangerous in hospitals: The BMJ credits this widespread belief (and the origin of those signs in hospitals warning against the use of mobile phones) to a Wall Street Journal article citing a medical journal report of more than 100 incidents of suspected electromagnetic interference with medical devices before 1993. But studies in England and the U.S. have found little in the way of interference and few serious effects. The BMJ cited a 2007 study that showed no interference at all in 300 tests in 75 treatment rooms. Indeed, the journal reported on a survey of anesthetists that showed use of mobile phones by physicians was associated with a reduced risk of medical error or injury resulting from delays in communication. Let's see how long it takes hospitals to react to these findings and change their policies with regard to cell phone use.
- Eating turkey makes people especially drowsy: Not so. Here, the myth is that the tryptophan in turkey causes the drowsiness. This amino acid is known to cause drowsiness, but the truth is that there's as much tryptophan in pork and cheese as there is in turkey. What's more, as the BMJ researchers noted that for tryptophan to promote sleep, you need to ingest it on an empty stomach (with no protein present) - something that's unlikely at Thanksgiving or Christmas dinner. Other factors are probably to blame for post-meal drowsiness: any big meal can make you sleepy because of a decrease in blood flow and oxygenation to the brain. And then, of course, there's the wine.
The researchers said that they selected the seven myths above because they had heard them so often that they thought they were true or might be true. They learned that they could be wrong and "need to question what other falsehoods we unwittingly propagate" in the practice of medicine.