Many common medical beliefs are untrue

Should we drink at least eight glasses of water a day? Does shaving hair cause it to grow back faster or coarser? Does reading in dim light ruin your eyesight?

These are just some of the common medical myths that are unproven or untrue, according to a study in this week’s Christmas issue of the BMJ.

Researchers in the United States selected seven medical beliefs, espoused by both physicians and members of the general public, for critical review. They then searched for evidence to support or refute each of these claims.

The quality of evidence was taken into account and instances in which no evidence supported the claim were noted.

The results show that all of these medical beliefs range from unproven to untrue. For example, they found no evidence supporting the need to drink eight glasses of water a day. In fact, studies suggest that adequate fluid intake is often met by the consumption of juice, milk, and even caffeinated beverages. Clinical evidence also points to the dangers of drinking excessive amounts of water.

The belief that we only use ten percent of our brains is refuted by studies of patients with brain damage, which suggest that damage to almost any area of the brain has specific and lasting effects on mental, vegetative, and behavioural capabilities, say the authors. Brain imaging studies also show that no area of the brain is completely silent or inactive.

The belief that hair and fingernails continue to grow after death may be an optical illusion caused by retraction of the skin after death, they add. 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, they say. 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.

Finally, expert opinion is that reading in dim light does not damage your eyes, and there is little evidence to support beliefs such as banning mobile phones from hospitals on the basis of electromagnetic interference.

Despite their popularity, all of these medical beliefs range from unproven to untrue, say the authors. They suggest that physicians should constantly evaluate the validity of their knowledge.

Source: British Medical Journal

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Citation: Many common medical beliefs are untrue (2007, December 21) retrieved 23 August 2019 from
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Dec 22, 2007
Umm... Excuse me, but I can personally vouch for the electromagnetic interference caused by cell phones.

Example: Sit close to a pair of computer speakers and make a call. The speakers will buzz loudly - I have observed this effect with multiple speaker systems, and at ranges of up to 15ft.

Maybe it won't crash a computer, but having an EM source like that in a hospital of all places seems somewhat foolhardy if it can be avoided. Accidents come from a convergence of factors, so let's not add any extras.


Dec 22, 2007
Also, a bit of speculation - I'd bet that a cellphone in someone's pocket during an x-ray would carry an induced voltage. Hard to say for sure without actual testing, but the circuit boards could probably fry and short.

This is just speculation though.


Dec 22, 2007
This is the kind of article that does NOT need to be on physorg. I'm sorry, perhaps you don't need to consume 8 glasses of water a day. But with the average salt intake today... and the fact that caffeine is a DIURETIC... you need to replace water. I would like to see these 'researchers' drink coffee all day, every day, for a week. Hell, if they can do it for a day and not wind up thirsty, I'll be very impressed. The rest of the points are just common sense. Any fool who has taken a high school biology class should be aware of all of these fallacies.

Oh, and I HATE that cell phone/speaker interaction by the way. I have 3 roommates, and they all use their phones a bit. If you upgrade your speaker wire (to a heavier gauge, or shielded... you won't have any more problems.)

Dec 22, 2007
I can only report my own experience on the water front. The three most dramatic effects were the elimination of my regular headaches(average one a week), the elimination of my dry and flaky skin and - alarming to my optician friend who discovered it - a 20% improvement in my short sightedness.

He was alarmed because he'd only previously seen such an improvement in diabetics. The reason was that their disease caused the same behaviour - involuntarily - that I was performing voluntarily; viz a significant increase in water consumption (Diabetics are permanently thirsty). This, apparently, causes the lens in the eye to "fill out" and, if you're shortsighted like I am, it improves your vision.

I have been on this regime for about 8 years now and have noticed nothing but beneficial effects. It also helps with general kydney function and in maintaining blood alkalinity. I have advised others to try it and most report similar benefits. The headache one is particularly common. It appears that about 90% of headaches are caused simply by dehydration. Fix that and you fix 90% of headaches. I genuinely haven't had one for 8 years. That alone is enough to keep me on my 3-4 pints of pure (filtered) water a day.

The argument that other fluids provide all the water we need is partly answered by bmcghie's point. Coffee, alchohol and many other "beverages" are diuretics. Even those that aren't often contain the water they need to flush through only the contents of the beverage. We seem to need the additional water to deal with all the other flushing.

Dec 22, 2007
In total, 8 (1 glass = 8oz) glasses of water is not bad that's only 64ounces. If you do the math that's really 5.33/day, 12 ounce glass(Fast food restaurants usually have 16oz ). I drink 1-2glasses of liquids per meal, so i meet the recommended. Besides, they aren't saying to gulp all 8 glasses of water in one sitting.

Haha i laughed pretty hard when i saw "optical illusion** caused by retraction of the skin", honestly? people need to consider that hair roots go fairly deep(fingernails too). I suppose surprise! Teeth are also longer, when the gums retract(*cough Gingivitis!) Approximate water in a human is 70%, we are little bodies of ocean, with ebb and flow :D

Eyes, no damage perhaps in the short run, but all that strain can eventually lead to damage...(Eyes dilate in dark conditions to see, but eyes also attempt to focus on text = conflict = strain) [Strain = stress = pissed off = no good]Check what stress can do, it's baffling.

Cellphones haha all electronics give off EM fields, consider usage in hospital when it needs to measure in microvolts, any slight disturbance may not harm the patient directly, but the delay in getting the proper image/info because of this disturbance can be serious or fatally harm in the long run. Perhaps banning cellphones hospital wide is unnecessary, though consider going towards sensitive areas of the hospital, its easier to have no/off cell (as standard) than say "oh crap".. Like what axemaster said, extra problems can be left behind. Besides, doctors or any health profession generally work with % of success, purpose is to increase chance not decrease it.

Dec 22, 2007
*sigh* Look people, give me a break. The folks who write these articles and the teams who make these discoveries are, how do I put this delicately...smarter than you. They do what you call "research" in order to come up this stuff, as opposed to reading a few articles on google and suddenly declaring themselves an electronic engineer or seeing themselves fit to play doctor. Do us all a favor, instead of hurling your "speculations" around, back up your rebuttals with actual facts and research before you rant and rave about how you know everything and the pros don't. And if you can't, then go back to watching Youtube and playing online poker and leave us in peace.

Dec 22, 2007
Plus...I don't know many doctors who would let you use your cell phone while getting an x-ray. First of all, they make you take off all your clothes and change into one of those fancy gowns that happen to be pocket-less. So good luck sneaking a cell phone into the room. Secondly, hospital equipment doesn't cost millions of dollars for nothing. Its made to be durable and highly accurate and thus they don't skimp out by using cheap parts and cutting corners. If my cell phone could interfere with them I would be very, very worried. Plus, if that were true hospitals would have to be completely shielded from outside cell and radio band waves. Those huge cell towers are thousands of times more powerful than your hand held phone, and if anything was going to cause your hospital equipment to go awry, then those bad boys would do it for sure.

Also, with the risk of using 'speculation' I would say that when I die, all the water in my body would, I don't know, dry up. Thus causing my skin to shrivel up, retract and oh say, make my fingernails look longer. Ask any mortician, when they prepare the bodies for the funeral viewing they use moisturizer to combat this effect. And ill take their word for it, since they do it for a living.

Dec 23, 2007
Good posts. About the cell towers though.. The signal strength dissipates proportionally to the inverse square of the distance. The interference from a cell phone resting on a machine is extreme compared to that from a reasonably distant cell tower. You can have fun with cell phone interference by putting it right up to a speaker. It's wild. It would be worthwhile for someone to do the math though (I'm sure it's been done). Again, the rest of what you said was on the right track.

Jan 02, 2008
Black is the new brown.

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