Medical Myths "Debunked"

Researchers find some medical myths are just nonsense

Sharon Kirkey, CanWest News Service

Published: Friday, December 21, 2007

Shaving doesn't make hair grow back faster, humans don't use just 10 per cent of their brains and they don't need to drink eight glasses of water a day.

So concludes a review of some of the most common medicine-related myths published in this week's Christmas issue of the British Medical Journal.

Two American researchers who searched for data to support myths espoused by doctors and the public alike, including that reading in dim light ruins your eyesight or that turkey makes people drowsy, found either no evidence to confirm the claims or studies proving them flat out wrong.

For example, the prevailing medical mantra that people need to ingest at least eight glasses of water daily appears to have originated with a 1945 recommendation from the American Nutrition Council that said people should drink the equivalent of about eight glasses of fluid per day.

Ignored in the original statement was that most of the fluid people need is found in food, especially fruits and vegetables, says Dr. Rachel Vreeman, co-author of the study and a fellow in children's health services research at Indiana University School of Medicine in Indianapolis.

"They also said that other things that people drink -- coffee, soda even -- should be included in this amount," Vreeman says. Frederick Stare, the prominent nutritionist and founder of the department of nutrition at Harvard's School of Public Health, went further: his recommendation -- without references -- that people consume around six to eight glasses per 24 hours included beer.

YOUR BODY KNOWS

Vreeman says the human body is remarkably efficient at regulating how much water it needs. "Your body tells you when you're thirsty." Taken to the extreme, too much water can be dangerous: In January, a 28-year-old California woman died of water intoxication after competing in a water-drinking contest run by a Sacramento radio station.

She was trying to win a video game system.

The myth that humans use only 10 per cent of their brains "goes against everything that you learn in medical school," Vreeman says. None of the different brain imaging studies reviewed show any gaps or inactive or dominant areas of the brain. "In the studies where they look at individual cells and how they function in terms of their metabolism, there are no parts of the brain that are not functioning or don't show that they are processing chemicals."

She and her co-author, Dr. Aaron Caroll, believe the myth arose in the early 1900s, propagated by early motivational speakers who wanted to convince people they had not reached their full potential.

"They essentially started telling people, if you tap into the 90 per cent of your brain that was not used you could go further. They really had no evidence to say that."

MORE MISCONCEPTIONS

More myths debunked in the study:

- Eating turkey makes people especially drowsy: Evidence shows that tryptophan, a chemical in turkey, can cause drowsiness, but turkey contains the same amount of tryptophan, gram per gram, as chicken and ground beef, Vreeman says. And other sources of protein, including pork, contain more tryptophan per gram than turkey.

Any big meal or holiday feast can make people sleepy because blood flow and oxygenation to the brain decrease. Wine also doesn't help.

- Hair and fingernails keep growing after death: It's an optical illusion, Vreeman says. After death, skin and other soft tissue dries out. The shrunken skin pulls back and retracts, making fingernails or hair more obvious or prominent. The actual growth of hair and nails, the authors report, "requires a complex hormonal regulation not sustained after death."

- Reading in dim light ruins your eyes: It does cause some eye strain and can make eyes feel dry and irritated, because people blink less when reading in sub-optimal light. It can also cause a temporary decrease in acuity, or how well you see. "But there is no evidence this causes any permanent problems," Vreeman says.

 Shaving causes hair to grow back faster or coarser: As early as 1928 a study showed shaving had no effect on hair growth. Shaving removes the dead part of hair, "not the living section below the skin's surface" so it's unlikely to affect how fast it grows back. What's more, "shaved hair lacks the finer taper seen at the ends of unshaven hair, giving an impression of coarseness," Vreeman and Caroll report.

- Mobile phones are dangerous in hospitals: The duo found no deaths caused by the use of a mobile phone in any medical facility and say 510 tests with 16 medical devices by the Mayo Clinic in 2005 concluded "the incidence of clinically important electromagnetic interference was 1.2 per cent."

Their literature search wasn't exhaustive. But, "I think these myths are of interest to everyone. Sometimes we believe things just because we've heard them from other people, especially 'experts'," Vreeman said.