I posted this on my blog but I'll re-post here, since it seems to be apropos to the discussion...
Seven Cherished Medical Beliefs: All Called Myths
By Crystal Phend, Staff Writer, MedPage Today
Published: December 21, 2007
INDIANAPOLIS, Dec. 21 -- As most physicians know, the evidence underpinning many medical beliefs is flimsy at best, but the backing for some common wisdom is downright ethereal.
Take the conviction that patients need to drink at least eight glasses of water a day, for instance. A myth, said Rachel C. Vreeman, M.D., of Indiana University here. No bona fide evidence.
"Most of us have probably heard that myth somewhere if not from our own doctors even," Dr. Vreeman said.
She and a colleague, Aaron E. Carroll, M.D., M.S., of the Regenstrief Institute here, debunked that and six other deeply entrenched medical beliefs in a review published in the end-of-year issue of the BMJ. This issue is traditionally devoted to off-beat or humorous, albeit legitimate, research results.
"The medical myths we give here are a light-hearted reminder that we can be wrong and need to question what other falsehoods we unwittingly propagate as we practice medicine," they wrote.
Advice to drink 64 oz of water per day likely stemmed from a 1945 recommendation that "a suitable allowance of water for adults is 2.5 liters daily in most instances," they said.
However, much like a game of telephone, Dr. Vreeman said, the message eventually got lost that "most of this quantity is contained in prepared foods."
Other studies have since shown that the typical diet with accompanying intake of juice, milk, coffee, and caffeinated drinks usually meets the body's fluid requirements, the investigators noted.
"There's not a number amount," Dr. Vreeman added. "It's more that you just need to pay attention to what your body wants."
Although no harm would be expected from drinking an extra eight glasses of water beyond fluid intake from other sources in the diet, excessive amounts could lead to water intoxication, hyponatremia, and death in the most extreme cases.
Another common belief -- that we use only 10% of our brains--has persisted for over a century, the researchers said. Some have attributed its origin to Albert Einstein but no records support this. Another source may have been self-improvement experts advocating tapping into latent abilities.
However, brain-imaging studies have shown no area of the brain that is completely inactive, the researchers said. Damage to almost any area of the brain causes specific, long-term deficits in mental, vegetative, and behavioral capabilities.
"Even micro-level localization, isolating the response of single neurons, reveals no gaps or inactive areas," they wrote. "Metabolic studies, tracking differential rates of cellular metabolism in the brain, show no dormant areas."
One myth from the grave is the belief that hair and fingernails continue to grow after death. This is an illusion on the basis of increased prominence from retraction of the skin around hair and nails as the body dehydrates after death.
"The actual growth of hair and nails, however, requires a complex hormonal regulation not sustained after death," the researchers said.
Other unproven and untrue myths in the review included:
- "Reading in dim light ruins your eyesight," a belief that probably stems from the sensation of difficulty focusing and drying because of a decreased blinking rate, which, although uncomfortable, do not persist.
- "Shaving causes hair to grow back faster or coarser," another illusion, as trimmed hair lacks the finer taper seen at the ends of unshaven hair and has not yet been lightened by sun or chemical exposures.
- "Mobile phones are dangerous in hospitals," which was disproved by a 2005 Mayo Clinic study that found only a 1.2% rate of clinically important interference. Also, rigorous testing in Europe that revealed minimal interference only at distances less than 1 m.
- "Eating turkey makes people especially drowsy," which although popularly attributed to tryptophan is more likely the result of reduced blood flow to the brain from a heavy holiday meal. Turkey has no more tryptophan per gram than chicken or ground beef and less than pork and cheese.
Belief in these statements is unlikely to cause harm, the researchers emphasized.
In a homily to physicians, the authors pointed out that "speaking from a position of authority, as physicians do, requires constant evaluation of the validity of our knowledge."
Other myths that the researchers hope to explore in the future include whether swallowed chewing gum stays in the body for seven years, how colds are acquired and treated, and especially, whether sugar makes kids hyperactive.
"That's one that none of my friends with kids are going to believe me when I tell them that it's not true," Dr. Vreeman said.
Likewise, she acknowledged that the report is unlikely to make much of a dent in propagation of these medical myths.
"These things are incredibly hard to get rid of," she said. "Other people besides us have pointed these out, but still the myths persist."
The authors reported no conflicts of interest.
Primary source: BMJ
Source reference:
Vreeman RC, Carroll AE, "Medical myths" BMJ 2007; 335: 1288-89.
