More medical myths: Turkey doesn't make you tired?

The answer: The British medical journal BMJ. Last month, the journal published a list of health myths related to the holidays.

It was the journal's second study into health-related myths that even many doctors believe. You can find the seven myths from the first study lower down in this story. But first, some perspective from Dr. Laura Mosqueda, the medical director of the UC Irvine Senior Health Center, who said after reading the myths that the most important message is not related to the medical beliefs at all.

"It is that we are susceptible to believing unproven concepts if they are repeated often enough by 'experts' (real or self-perceived/self-proclaimed)," Mosqueda said.

So here are the other seven myths.

1. Drink eight glasses of water each day

The authors found references as early as 1945 suggesting that healthy people should stay hydrated by drinking eight glasses of water each day. But they say there's a complete lack of evidence supporting that recommendation. Studies also show that most people get enough fluids through daily consumption of juice, milk and even caffeinated drinks.

2. People only use 10 percent of their brains

This myth has been around for more than a century. Some believe it came from Albert Einstein, although the authors found no evidence of that. What they did find were studies that show people use much more than 10 percent of their brains. For example, when almost any area of the brain is damaged, it has "specific and lasting effects on mental, vegetative and behavioral capabilities." Also, imaging studies have found no area of the brain is completely inactive.

3. Hair and fingernails keep growing after death

While it's impossible for the body to continue the complex hormone regulation needed to cause hair and nails to grow after death, this myth does have a basis in a biological phenomenon that sometimes occurs after death.

When someone dies, dehydration of the body can cause the skin around the hair or nails to retract, creating the appearance of increased length. But the authors say this is an optical illusion.

4. Shaving causes your hair to grow back faster, darker or thicker

Several studies show that shaving has no effect on the thickness or rate of new hair growth. But because shaved hair is blunt, and doesn't have the finer taper at the ends of unshaven hair, it can give an impression of being coarse. And new hair sometimes appears darker because it has not yet been lightened by the sun or other chemical exposures.

5. Reading in dim light ruins your eyesight

While reading in dim light can cause eye strain, and the uncomfortable effects that go along with it such as dryness and difficulty focusing, it does not cause permanent damage, the authors say.

6. Eating turkey makes you especially tired

If turkey contains tryptophan, and science has found that tryptophan can cause drowsiness, how is this medical belief a myth?

The authors say turkey doesn't contain "an exceptional amount of tryptophan." In fact, turkey, chicken and minced beef contain nearly the same amounts of the amino acid. Other proteins, such as pork or cheese, contain more tryptophan per gram than turkey.

Perhaps the reason turkey has long been accused of making people extra sleepy is because of all the overeating we do on Thanksgiving. Studies show that eating any large, solid meal can make you tired because blood flow and oxygenation to the brain decreases. Plus, meals that are high in protein or carbohydrates can cause sleepiness. So can wine.

7. Cell phones cause significant electromagnetic interference in hospitals

Hospitals widely banned cell phone use after a front page Wall Street Journal story cited an article detailing more than 100 reports of suspected electromagnetic interference with medical devices before 1993. But an Internet search by the study's authors could not find any cases of death caused by use of a mobile phone in a hospital. They did find reports of less serious events, such as false alarms or incorrect medical readings.

Meanwhile, subsequent studies show little or no interference. For example, a 2007 study examining mobile phones "used in a normal way" found no interference in 300 tests in 75 treatment rooms.

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