Does shaving hair cause it to grow back faster or thicker? Does reading in dim light ruin your eyesight? Do we really use only 10 per cent of our brains?
These are just some of the common medical myths that it appears that even a lot of doctors still believe, even though none have ever been proven -- or have been proven to be completely wrong.
Researchers in the United States selected seven medical beliefs, long assumed to be true by both doctors and the general public and then searched for evidence to support or refute each of these claims. Their results are published in the holiday issus of the
The results show that all of the beliefs are actually myths. Here are a few from the list:
We only use 10 per cent of our brains
This myth is refuted by brain imaging studies which show that not a single area of the human brain is completely inactive. The researchers also pointed to studies of patients with brain damage, which suggest that damage to almost any area of the brain has specific effects on mental, vegetative, or behavioural capabilities.
Shaving hair makes it grow back faster, thicker and darker
This one is likely a kind of optical illusion. When hair first comes in after being shaved, it grows with a blunt edge on top. Over time, the blunt edge gets worn so it may seem thicker than it actually is. Sun naturally bleaches hair over time, so hair that is just coming in after being shaved may appear darker, but actually is no darker than any new hair growth.
The researchers say that this myth was refuted back in 1928, when a randomized clinical trial compared hair growth in shaved patches to growth in non-shaved patches. The hair that replaced the shaved hair was no thicker, nor did not grow in faster. And yet this myth has persisted almost 80 years after it was disproved.
Fingernails and hair grow after death
Most physicians the study authors queried initially assumed this belief was true. But when they thought about it, they knew it couldn't possibly be; the actual growth of hair and nails requires bodily functions that couldn't possible be present after death.
This myth also likely persists because of an optical illusion. After the body dies, the skin dries out and as it does so, it retracts from nailbeds and thins out along the scalp, explains co-author Dr. Rachel Vreeman, a pediatrics research fellow at the Indiana University School of Medicine.
"As the skin is shrinking back, the hair looks more prominent or sticks up a bit," explains Vreeman.
People should drink at least eight glasses of water a day
This advice has been promoted as healthful as well as a useful dieting or weight control strategy. But when the researchers looked further, they found no medical evidence to suggest that anyone needs that much water.
Vreeman thinks this myth can be traced back to a 1945 recommendation from the U.S. Nutrition Council that a person consume 64 ounces of fluid a day. But an important part of the Council's recommendation has been lost over the years: that amount also includes the large amount of fluid contained in food, especially fruits and vegetables, as well as in the other beverages that people drink every day.
The study authors note that drinking excess water can be dangerous, since it could lead to the potentially fatal condition of water intoxication.
Reading in low light damages your eyes
Generation after generation of parents have warned children (future doctors included) that reading in poor light ruins your eyesight. But the study authors found no evidence that reading in dim light causes permanent eye damage. It is true, they say, that dim light can cause eye strain, causing some temporarily decreased acuity. But after rest, the eyes return to their full potential.
Eating turkey makes you sleepy
Many people believe that the tryptophan in turkey can make you sleepy after a big turkey dinner. But the researchers found that turkey doesn't contain an exceptional amount of tryptophan. In fact, turkey, chicken, and ground beef contain about the same amount of tryptophan. And protein sources such pork and Swiss cheese contain even more tryptophan per gram than turkey.
Most likely, according to the study authors, this myth gained credence because turkey is often consumed during large, heavy dinners. It's the total content of the meal that wears the body out and makes one feel lethargic.
Cellphones can cause electromagnetic interference in hospitals
Again, the evidence on this one is just not there, with conflicting results on the numerous studies that have been done on this issue.
The authors say that no death has ever been reported by the use of a cell phone in a hospital or medical facility. Less serious incidents, including false alarms on monitors, malfunctions and incorrect readings on cardiac monitors, have occasionally been reported.
They note that even though some older cellphones caused interference, recent technological improvements have lessened this minimal interference.
Co-author Dr. Aaron Carroll, assistant professor of pediatrics at Indiana University says her team decided to conduct the study because they knew that these were myths that even
physicians accepted -- even though doctors are taught to rely only on evidence-based research -- and were passing this information along to their patients.
"Until someone takes the time to question and look for evidence, medical myths will remain accepted beliefs. We have tried to show through science and research why certain widely accepted beliefs are untrue," said Carroll.
Vreeman adds that physicians should constantly re-evaluate the validity of their knowledge.
"Sometimes you really have to look back on things already in your head or things you already believe to be true and reinvestigate or investigate for the first time whether those things are true," Vreeman says.
Vreeman and Carroll are currently working on a book examining dozens of other popular medical beliefs to see if they are true, false or unproven.
