Medical myths exposed as untrue

* Some claim drinking eight glasses of water a day leads to good health,
while reading in dim light damages eyesight. *

Others believe we only use 10% of our brains or that shaving legs causes
hair to grow back thicker.

But a review of evidence by US researchers surrounding seven
commonly-hold beliefs suggests they are actually "medical myths".

Some are utterly untrue, while others have no evidential proof, the
British Medical Journal reports.

Researchers from the Indiana University School of Medicine in
Indianapolis hunted medical literature for evidence on each claim.

They found no evidence supporting the need to drink eight glasses of
water a day.

* Medical myths *

In fact, studies suggest that adequate fluid intake is often met by
drinking juice, milk, and even caffeine-rich tea and coffee.

Data also suggests drinking excessive amounts of water can be dangerous.

The belief that we only use 10% of our brains appears to be completely
untrue.

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.

    * Absence of evidence does not necessarily mean absence of effect *
Dr David Tovey
Editor of Clinical Evidence journal

Brain imaging studies also show that no area of the brain is completely
silent or inactive.

And the belief that hair and fingernails continue to grow after death
may be an optical illusion caused by retraction of the skin after death.

The actual growth of hair and nails requires a complex interplay of
hormonal regulation not present after death.

Again, illusion may be to blame for the belief that shaving hair causes
it to grow back faster, darker, and coarser, report author Rachel
Vreeman told the BMJ.

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.

Again, expert opinion is that reading in 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.

Finally, eating turkey - and the tryptophan amino acid it contains -
does not make people especially drowsy.

Indeed, turkey, chicken and minced beef contain similar amounts of
tryptophan.

   
THE SEVEN MEDICAL BELIEFS
Drink at least eight glasses of water a day
We use only 10% of our brains
Hair and fingernails continue to grow after death
Reading in dim light ruins your eyesight
Shaving causes hair to grow back faster or coarser
Mobile phones are dangerous in hospitals
Eating turkey makes people especially drowsy

The researchers explained: "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."

Dr David Tovey, editor of Clinical Evidence journal, said: "The
difficulty is it is often hard to disprove a theory.

"On the flip-side, absence of evidence does not necessarily mean absence
of effect.

"Where reliable evidence becomes really important is in helping people
make serious decisions about harms and risks.

"Many of these 'myths' are innocuous. However, we are still finding
evidence that runs contrary to current practice and what we expect."

He gave the example of the relatively recent U-turn in advice over
sleeping positions for babies to cut cot deaths.

Experts now recommend babies are positioned on their backs when sleeping
to reduce the risk of sudden infant death.