Step on a crack and you’ll break your mother’s back. An apple a day keeps the doctor away. Sit too close to the TV and you’ll suffer brain damage.

These are but a few old wives’ tales anyone over age 10 can dispel with a quick search on the Internet.

And there’s more.

Drink at least eight glasses of water a day for optimum health. Humans use only 10 percent of their brains. A chemical found in turkey makes people lethargic.

Many people – even some doctors – believe these to be tried-and-true health facts, but according to a new study published in the British Medical Journal, many of these “facts” are unproven or flatly untrue.

The study, “Medical Myths Even Doctors Believe,” was compiled by researchers at the Indiana University School of Medicine, included myths that people only use 10 percent of their brains and that hair and fingernails continue to grow after we die.

The surprising findings are that all these beliefs turned out to be bunk.

“We got fired up about this because we knew that physicians accepted these beliefs and were passing this information along to their patients ... we didn’t set out to become myth busters,” Dr. Aaron Carroll, assistant professor of pediatrics and a Regenstrief Institute Inc. affiliated scientist, told StatePoint.net.

The first belief they explored was that people should drink at least eight glasses of water a day. This advice has long been promoted as healthful, as well as a useful dieting or weight-control strategy.

“When we examined this belief, we found that there is no medical evidence to suggest that you need that much water,” said Dr. Rachel Vreeman, a pediatrics research fellow and co-author of the new study in an interview with StatePoint.

Vreeman believes this myth can be traced back to a 1945 recommendation from the Nutrition Council. But an important part of the Council’s recommendation has been lost over the years: The large amount of fluid contained in food, especially fruits and vegetables, as well as in the coffee and soda people drink daily, should be included in the recommended total.

As a matter of fact, drinking excess water can be dangerous, resulting in water intoxication and even death, the study authors noted.

While not doctor recommended, many local residents recall health myths told to them by mothers and grandmothers throughout their childhood, the most popular being that of not going out in the cold to avoid catching a cold.

“This came from my mother-in-law many years ago,” said Pam Moore. “Now that I am all grown up, I know that germs cause colds, not cold.”

Sammye Rusco had a similar version of the cold myth.