Drinking 8 glasses of water a day and other medical myths

The Christmas edition of the British Medical Journal exposes seven medical myths as just that.

1 Drink at least 8 glasses of water a day
This is a common myth, perpetuated by the popular press and less well educated dieticians and even some doctors. Rachel Vreeman and colleagues suggest that the myth may have originated as early as 1945 with a recommendation that stated that a suitable allowance of water for most adults is 2.5 litres daily. What most people ignore is the final sentence of the recommendation that says that most of this water can be found in prepared foods. In fact there is no evidence at all that consuming an extra 8 glasses of water daily is at all beneficial. In fact, it may be dangerous if taken on top of ordinary food and drink, leading to water intoxication, hyponatraemia and even death.

2 We only use 10% of our brains
This is a particularly old adage and is apparently ascribed to Einstein in the first instance. It arose as early as 1907 - when neuroscience was not the subject it is today - and was eagerly advocated by proponents of self-improvement and tapping into latent and unrealised potential - no doubt also advocating expensive programmes supporting their theories. But, now we have evidence from brain damage, brain imaging, localisation of function, analysis of the microstructure of the brain and metabolic studies that show that we do indeed use far more than 10% of our brains.

3 Hair and fingernails continue to grow after death
This popularly macarbre myth probably has its basis in the fact that after death the skin dehydrates and shrinks, so hair and nails could appear to get longer. There is absolutely no basis in fact. Once you are dead, nothing grows!

4 Shaving hair causes it to grow back faster, darker or coarser
Evidence presented as early as 1928 showed that shaving had no effect on hair growth. In fact, shaving removes the dead portion of hair just below the skin and not the growing portion. Shaved hair is cut off at the tip, rather than being tapered, which can result in a coarse appearance and may be darker because it hasn't been lightened by exposure to the sun.

5 Reading in dim light ruins your eyesight
Simply not true. Reading in dim light may result in eye strain, with temporary effects, but it doesn't result in permanent damage to the structure of the eye. When you read in dim light you don't blink as much, which may cause dry eyes. But all this is reversed when you are back in good light conditions.

6 Eating turkey makes you drowsy
This myth arises from the fact that turkey, and other poultry, contains tryptophan - an amino acid that is involved in sleep and mood control and which can make you drowsy. In fact turkey doesn't contain any more tryptophan than other poultry or indeed minced beef. So it's probably what you imbibe with the turkey that is the culprit!

7 Cell phones cause considerable electromagnetic interference in hospitals
In fact the authors could find absolutely no evidence of any deaths caused by the use of cell phones in a hospital or other medical facility. They did find occasional reference to interference with monitors or ECG machines. However, an article on the front page of the Wall Street Journal reporting a journal article published in 1993 that cited more than 100 reports of suspected interference with medical devices lead to most hospitals banning cell phones on their premises. But a 2007 study of cell phones, used "in the normal way", showed no evidence of interference of any kind in 300 tests in 75 treatment rooms. In fact, another study of anaesthetists showed that using cell phones reduced the incidence of medical error or injury resulting from delays in communication.

See the full text of the article here http://www.bmj.com/cgi/content/short/335/7633/1288