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Medical myths

BMJ 2007; 335 doi: (Published 20 December 2007) Cite this as: BMJ 2007;335:1288
  1. Rachel C Vreeman, fellow in children’s health services research1,
  2. Aaron E Carroll, assistant professor of paediatrics2
  1. 1Children’s Health Services Research, Indiana University School of Medicine, Indianapolis, IN, USA
  2. 2Regenstrief Institute, Indianapolis, IN, USA
  1. Correspondence to:R C Vreeman rvreeman{at}

    Sometimes even doctors are duped, say Rachel C Vreeman and Aaron E Carroll

    Physicians understand that practicing good medicine requires the constant acquisition of new knowledge, though they often assume their existing medical beliefs do not need re-examination. These medical myths are a light hearted reminder that we can be wrong and need to question what other falsehoods we unwittingly propagate as we practice medicine. We generated a list of common medical or medicine related beliefs espoused by physicians and the general public, based on statements we had heard endorsed on multiple occasions and thought were true or might be true. We selected seven for critical review:

    • People should drink at least eight glasses of water a day

    • We use only 10% of our brains

    • Hair and fingernails continue to grow after death

    • Shaving hair causes it to grow back faster, darker, or coarser

    • Reading in dim light ruins your eyesight

    • Eating turkey makes people especially drowsy

    • Mobile phones create considerable electromagnetic interference in hospitals.

    We used Medline and Google to search for evidence to support or refute each of these claims. Because “proving a negative” can be challenging, we noted instances in which there was no evidence to support the claim.

    People should drink at least eight glasses of water a day

    The advice to drink at least eight glasses of water a day can be found throughout the popular press.w1-w4 One origin may be a 1945 recommendation that stated: A suitable allowance of water for adults is 2.5 litres daily in most instances. An ordinary standard for diverse persons is 1 millilitre for each calorie of food. Most of this quantity is contained in prepared foods.w5 If the last, crucial sentence is ignored, the statement could be interpreted as instruction to drink eight glasses of water a day.w6

    Another endorsement may have come from a prominent …

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