The Dec. 22, 2007, edition of the British Medical Journal corrects seven medical myths commonly espoused by doctors and widely believed by the public. The following is an excerpt of the article, which is available at: www.bmj.com/cgi/content/full/335/7633/1288.

MYTH: YOU SHOULD DRINK AT LEAST EIGHT GLASSES OF WATER A DAY
FACT: Studies suggest that adequate fluid intake is usually met through typical daily consumption of juice, milk and even caffeinated drinks. In contrast, drinking excess amounts of water can be dangerous, resulting in water intoxication, sodium deficiency and even death.

MYTH: WE USE ONLY 10 PERCENT OF OUR BRAINS
FACT: Evidence from studies of brain damage, brain imaging, localisation of function, microstructural analysis and metabolic studies show that people use much more than 10 percent of their brains. Studies of patients with brain injury suggest that damage to almost any area of the brain has specific and lasting effects on mental and behavioral capabilities. Numerous types of brain imaging studies show that no area of the brain is completely silent or inactive. The many functions of the brain are highly localised, with different tasks allocated to different anatomical regions. Detailed probing of the brain has failed to identify the “non-functioning” 90 percent. Even micro-level localisation, isolating the response of single [neurons], reveals no gaps or inactive areas. Metabolic studies, tracking differential rates of cellular metabolism within the brain, reveal no dormant areas.

MYTH: HAIR AND FINGERNAILS CONTINUE TO GROW AFTER DEATH
FACT: Dehydration of the body after death, and drying or desiccation may lead to retraction of the skin around the hair or nails. The skin’s retraction can create an appearance of increased length or of greater prominence because of the optical illusion created by contrasting the shrunken soft tissues with the nails or hair. The actual growth of hair and nails, however, requires a complex hormonal regulation not sustained after death.

MYTH: SHAVING HAIR CAUSES IT TO GROW BACK FASTER, DARKER OR COARSER
FACT: Shaving removes the dead portion of hair, not the living section lying below the skin’s surface, so it is unlikely to affect the rate or type of growth. Shaved hair lacks the finer taper seen at the ends of unshaven hair, giving an impression of coarseness. Similarly, the new hair has not yet been lightened by the sun or other chemical exposures, resulting in an appearance that seems darker than existing hair.

MYTH: EATING TURKEY MAKES PEOPLE ESPECIALLY DROWSY
FACT: Scientific evidence shows that tryptophan is involved in sleep and mood control and can cause drowsiness. Turkey does not contain an exceptional amount of tryptophan. Turkey, chicken, and minced beef contain nearly equivalent amounts of tryptophan (about 350 mg per 115 g), while other common sources of protein, such as pork or cheese, contain more tryptophan per gram than turkey. Any effects of the tryptophan in turkey are probably minimized by consuming it in combination with other food, which would limit its absorption. Other physiological mechanisms explain drowsiness after meals. Any large solid meal can induce sleepiness because blood flow and oxygenation to the brain decreases.

MYTH: MOBILE PHONES CREATE CONSIDERABLE ELECTROMAGNETIC INTERFERENCE IN HOSPITALS
FACT: At the Mayo Clinic in 2005, in 510 tests performed with 16 medical devices and six mobile telephones, the incidence of clinically important interference was 1.2 percent. Similarly rigorous testing in Europe found minimal interference and only at distances less than one meter. Recent technological improvements may be lessening even this minimal interference. A 2007 study, examining mobile phones “used in a normal way,” found no interference of any kind during 300 tests in 75 treatment rooms. In contrast, a large survey of anesthesiologists suggested that use of mobile phones by doctors was associated with reduced risk of medical error or injury resulting from delays in communication.