Medical myths laid to rest

New research from the United States has revealed that a number of commonly-held medical beliefs are in fact just medical myths.

Such beliefs cover virtually the entire gamut - from the danger of mobile phones to shaving legs which causes hair to grow back thicker.

A review of evidence by researchers from the Indiana University School of Medicine in Indianapolis surrounding seven commonly-hold beliefs suggests they are actually "medical myths".

According to researchers Aaron Carroll of the Regenstrief Institute in Indianapolis and Rachel Vreeman of the Indiana University School of Medicine, some are completely untrue, while others have no evidential proof as their basis.

The seven beliefs investigated were based on ideas and conversations the authors had heard endorsed on a number of occasions which many doctors thought were true.

They were:-

• Everyone must drink at least eight glasses of water a day.

• We only use 10% of our brains.

• Hair and fingernails continue to grow after death.

• Mobile phones are dangerous in hospitals.

• Eating turkey makes you especially drowsy.

• Reading in dim light ruins your eyesight.

• Shaving causes hair to grow back faster or coarser.

The researchers trawled through medical literature for evidence on each claim and found no evidence to support them.

They say the need to drink eight glasses of water a day and adequate fluid intake is often met by drinking juice, milk, and even caffeine-rich tea and coffee; some research even suggests that drinking excessive amounts of water can be dangerous.

The belief that we only use 10% of our brains also appears to be completely untrue as studies of patients with brain damage suggest that damage to almost any area of the brain has specific and lasting effects on mental, vegetative and behavioural capabilities and brain imaging studies show that no area of the brain is completely silent or inactive.

Hair and fingernails which appear to continue to grow after death may be an optical illusion caused by retraction of the skin after death, as such growth requires a complex set of precisely regulated hormones, which do not continue after death.

Shaving causes hair to grow back faster or coarser is again an illusion possibly because the stubble resulting from shaving grows out without the finer taper seen at the ends of unshaven hair, giving the impression of thickness and coarseness.

Experts say that reading in a dim light does not damage your eyes, and there is little evidence to support the banning mobile phones from hospitals on the basis of electromagnetic interference.

Eating turkey does not make people especially drowsy but any large meal can induce sleepiness because blood flow and oxygenation to the brain decrease, and meals rich in protein or carbohydrate may cause drowsiness; wine may also play a role.

The two doctors wanted to remind their colleagues that anyone could get things wrong and suggest that doctors think twice about commonly held ideas that might not be based on evidence.

The study is published in the British Medical Journal.