UNDER THE MICROSCOPE:I RECENTLY CAME across a very entertaining article entitled "Mixed Messages: Medical Myths", by RC Vreeman and AE Carroll, British Medical Journal(BMJ), Vol 335, pp1288-1289, December 22nd, 2007. The authors critically examined seven medically related beliefs commonly endorsed by physicians and accepted by the public, seeking the under- pinning evidence where it exists and exposing the lack of evidence where none exists.
Belief No 1: People should drink at least eight glasses of water a day.This is so commonly believed that many people are prepared to lug around heavy bottles of water with them all day. The advice is interpreted to mean you should drink at least 8 glasses of water per day in addition to your normal eating and drinking of beverages such as tea/coffee and soft drinks.
But the fact is, and I wrote a column on this topic not long ago, there is no evidence to support the advice to drink eight glasses of water a day. Studies show that you get adequate fluid intake through typical daily intake of milk, juice, tea, coffee and soft drinks.
Belief No 2: We only use 10 per cent of our brains.Some people think this claim was originally made by Albert Einstein, but there is no record that he ever made such a statement. How would he know anyway? Einstein was a physicist, not a neurophysiologist. In fact studies of the brain, including brain imaging, localisation of function and metabolic studies, reveal no dormant areas. Brain injury studies show that damage to almost any part of the brain has specific effects on capabilities whether mental, vegetative or behavioural.
Belief No 3: Fingernails continue to grow after death.This is untrue because growth of nails and hair requires sophisticated hormonal regulation not possible after death. The myth may have originated in a description given in the book All Quiet on the Western Front. Johnny Carson further popularised the notion with his oft-quoted joke: "For three days after death, hair and fingernails continue to grow, but phone calls taper off'." Dehydration of the body post-mortem may cause the skin around fingernails to retract thereby creating the appearance of increased nail length.
Belief No 4: Shaving hair causes it to grow back faster and thicker.Scientific studies have shown that shaving has no effect on hair growth. Normal strands of hair taper gradually towards their ends, but shaved hairs lack this taper and consequently give the impression of coarseness or thickness. The part of a hair that is living lies beneath the skin and remains unaffected by shaving. Shaving does not affect rate or type of growth.
Belief No 5: Reading in poor light ruins your eyesight.The great majority of studies in this area do not support this belief, but one review concluded that reading in dim light could result in impaired eye growth and refractive error. It is true that reading in poor light can lead to eye strain and discomfort from squinting, but, these effects do not persist. Rates of myopia have increased over the past 100 years despite the fact that lighting conditions for reading were surely better using electric light than in previous centuries when people had to rely on candles and oil lamps.
Belief No 6: Eating turkey makes you feel especially drowsy.This belief seems to derive from the fact that turkey contains the amino acid tryptophane which is involved in sleep and mood control and can cause drowsiness. However, turkey contains no more tryptophane than chicken or beef and less than pork or cheese. It is a myth that eating turkey particularly disposes one to drowsiness. Many of us only eat turkey for Christmas dinner when we accompany it with lots of stuffing, ham, vegetables and wine. Naturally you will feel drowsy after all of this.
Belief No 7: Mobile phones create considerable electromagnetic interference in hospitals.There have been reports that mobile phones interfere with sensitive medical equipment such as cardiac monitors and some hospitals ban the use of mobile phones in intensive care units. But the evidence shows that the extent of interference is quite low.
The authors quote a Mayo Clinic Study in 2005 where 510 tests were performed with 16 medical devices and six mobile phones. The incidence of clinically important interference was 1.2 per cent. Also, interference usually occurs only at distances less than 1 metre. Another 2007 study found no interference at all during 300 tests in 75 treatment rooms.
The authors recommend that physicians take care to evaluate the evidence supporting all of their medical decision-making. Many physicians believe in some of the seven myths described above. This is unlikely to cause any harm but recommending other medical treatments for which there is little evidence could cause harm.
William Reville is associate professor of biochemistry and public awareness of cience officer at UCC – http://understandingscience. ucc.ie
