Turkey makes you drowsy. Dim light ruins your eyes. Drink at last eight glasses of water a day. These are some of the medical myths that even doctors believe, reports the British Medical Journal.
Researchers from the Indiana University School of Medicine made a list of common medical beliefs espoused by physicians and the general public. They included statements they had heard endorsed by doctors on multiple occasions. The result is a seven-item list of medical and health myths that are widely repeated by doctors and in the media, all of which either aren’t true or lack scientific evidence to support them.
The study authors, Dr. Rachel C. Vreeman and Dr. Aaron E. Carroll, said that while doctors realize good medicine requires them to constantly learn new things, they often forget to reexamine their existing medical beliefs. “These medical myths are a lighthearted reminder that we can be wrong and need to question what other falsehoods we unwittingly propagate as we practice medicine,” wrote Dr. Vreeman and Dr. Carroll.
Here are the seven medical myths they identified.
1. People should drink at least eight glasses of water a day.
The article authors found no scientific evidence for this advice, although they found several unsubstantiated recommendations in the popular press. The source may be a 1945 article from the National Research Council, part of the National Academy of Sciences, which noted that a “suitable allowance” of water for adults is 2.5 liters a day, although the last sentence noted that much of it is already contained in the food we eat.
“If the last, crucial sentence is ignored, the statement could be interpreted as instruction to drink eight glasses of water a day,” Dr. Vreeman and Dr. Carroll noted. “Existing studies suggest that adequate fluid intake is usually met through typical daily consumption of juice, milk and even caffeinated drinks.”
2. We use only 10 percent of our brains.
The belief that we use only 10 percent of our brains has persisted for nearly a century, the authors noted. Sometimes the claim is attributed to Albert Einstein, but no reference or statement has ever been recorded. The study authors found references to this myth as early as 1907 and noted that it’s often repeated by people advocating the power of self-improvement.
However, the authors said that evidence from studies of brain-damaged people, imaging and metabolic studies and other brain research shows that people use much more than 10 percent of their brains. “Numerous types of brain imaging studies show that no area of the brain is completely silent or inactive,” wrote the authors. “Detailed probing of the brain has failed to identify the ‘non-functioning’ 90 percent.”
3. Hair and fingernails continue to grow after death.
The claim has been repeated in movies and talk-show monologues, but it’s not true. The growth of hair and nails requires “a complex hormonal regulation” that stops after the body dies. The reason for the long-held belief may be that dehydration of the body after death, and subsequent shrinking of soft tissue, can create the illusion of growth of hair and nails.
4. Shaving hair causes it to grow back faster, darker or coarser.
This common belief is often repeated in the media and reinforced when coarse stubble appears on the body after shaving. A 1928 clinical trial showed that shaving had no effect on hair growth, a finding confirmed by more recent studies. When hair grows back after shaving, it seems coarse because it doesn’t have the fine taper of unshaved hair. It seems darker because it hasn’t been exposed to the sun like the previously unshaved hair.
5. Reading in dim light ruins your eyesight.
The idea that dim light ruins eyesight probably has its origins in eye strain, said the study authors. Bad lighting makes it hard to focus, makes you blink less and leads to dry eyes, particularly if you’re squinting. So reading in dim light is uncomfortable, but it doesn’t cause permanent damage.
6. Eating turkey makes people especially drowsy.
This myth stems from the fact that turkey contains tryptophan, an amino acid found in proteins and essential to the human body. Scientific studies show that sleep and mood are affected by tryptophan.
However, turkey does not contain an exceptional amount of tryptophan. Chicken and beef contain about the same amount, and pork and cheese contain more tryptophan per gram than turkey. Because turkey is consumed with other foods, absorption of tryptophan from turkey is minimal, noted the authors. The myth likely stems from the fact that everyone feels drowsy after eating a large meal because the body is using energy to digest food and blood flow and oxygenation to the brain decreases. Large meals in the United States usually occur around Thanksgiving and Christmas, holidays during which turkey is often served.
7. Cellphones create considerable electromagnetic interference in hospitals.
Anecdotal reports persist that cellphones create false alarms on monitors and malfunctions in infusion pumps. After publication of a medical journal article citing more than 100 reports of suspected electromagnetic interference with medical devices before 1993, The Wall Street Journal published a front page article on the topic. As a result, many hospitals banned the use of cellphones, perpetuating the belief.
But the study authors found no evidence to support it. At the Mayo Clinic in 2005, in 510 tests performed with 16 medical devices and six mobile phones, the incidence of clinically important interference was 1.2 percent. A 2007 study that examined cellphones “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 found that use of cellphones by doctors was associated with a 22 percent reduction in medical error resulting from delays in communication.
Update: After reading dozens of reader comments on this post, the study authors have added their own response. To see what they have to say read comment #101 below.
Healthy living doesn't happen at the doctor's office. The road to better health is paved with the small decisions we make every day. It's about the choices we make when we buy groceries, drive our cars and hang out with our kids. Join columnist Tara Parker-Pope as she sifts through medical research and expert opinions for practical advice to help readers take control of their health and live well every day. You can reach Ms. Parker-Pope at 
The easiest and most pleasurable way to eat well is to cook. Recipes for Health offers recipes with an eye towards empowering you to cook healthy meals every day. 
From 1 to 25 of 266 Comments
The real myth is that people use AS MUCH AS ten percent of their brains. Most people seem to use almost none.
— ACWWhile I’ll be the first to admit that physicians make mistakes and can be misinformed, it is, without citing adequate data, quite disingenuous to trumpet in headline fashion that doctors believe certain medical myths.
One can find certain doctors who believe in just about anything, but we really don’t know WHAT PERCENTAGE of docs believes in or disseminates these medical myths.
Without providing those data, the article may be giving the false impression that vast numbers of docs are disseminating scientifically unproven information.
Such false impressions do little to improve doctor-patient relations.
Ms. Pope, I’m sorry you did not provide these critical data in your article, or in the absence of such, noted the lack of data.
From TPP — Thanks for your comments. The report authors didn’t provide that data.
— Jack F. Bukowski, MD, PhD8. Dairy products are good for you.
9. People with high cholestorol should take drugs, instead of ceasing to eat the insane amounts of fat and protein they’re eating.
10. A heart bypass operation is normal medicine, but a vegan diet is “radical” and unreasonable.
— k2I particularly liked the dispelling of the myth reference dim lighting 2. the use of cell phones in hospitals and the drinking of water
— Cam OgleThanks for a delightful article. At least none of the myths cited cause severe adverse side effects. I wonder what other beliefs commonly held by physicians do cause adverse sided effects.
Science Editor
— Reader001http://www.polijam.com
Your Guide to News Around the Web
Who did the studies toward these conclusions. My conclusion is that we need be aware of everything we read.
— lana adamsNo. 8. If you go swimming within 60 minutes of eating you will instantly get a cramp, be sucked under the water, and die. This will break your mother’s heart.
Oh, sorry, that’s for the old wives article.
— Andrew@k2
8: Well, the gene making it possible for us to eat dairy products evolved about 5000 years ago. We’re just getting better and better at digesting those products.
9: my wife has high cholesterol. She’s almost always eaten a near vegetarian diet. She’s not the only person like this. This response highlights another myth which is that all patients respond the same way to diets and drugs. Fortunately, doctors are starting to come around and understand how everyone responds differently. Only advocates of extreme measures conveniently ignore this little aspect of patient behavior.
10: another myth about medical practitioners. For some reason, the myth persists that doctors and other medical practitioners just want to throw some solution at a patient and collect their money. I’ve met one or two doctors like that but I fire them and go on to someone that cares. In the case of cardiologists, I don’t know of a single cardiologist that thinks of a heart bypass as normal medicine. They clearly know that is a result of a series of failures of health and with preventative measures the operation could have been avoided or at least delayed.
A vegan diet is unnatural and driven more by philosophical motivations than good health. But it’s most important to remember no one diet fits all people. The vegan diets give me high triglycerides and migraines. Only if I eat a low-fat high-protein diet (including large amounts of animal protein) do my triglycerides come down and migraines go way. On the other hand, I know a very successful marathoner that only eat vegetarian. Everybody’s different and your path is not their path.
— country mouseAnother one:
8. Alcohol should not be consumed while taking antibiotics.
Don
— eromlignodThe notion of drinking eight glasses of water a day has been hijacked by the (insatiable) bottled water industry, perhaps the most shocking and obvious result of marketing in our country’s history, certainly in my lifetime. The waste of it and the waste it causes would be laughable if it were not so pathetic and destructive. Once again the market place finds something we absolutely do not need and makes us pay through the nose for it. Congratulations!
— charlieI’ve been using all my brain all these years? Wow, I’m in deep trouble.
— Don#3 - Your # 9 is not exactly a myth. If you take a basic biochemistry class, you will learn that the enzyme which makes cholesterol is actually inhibited by cholesterol itself. So, while people with high cholesterol should learn to watch their diet, sometime the only way to significantly lower their cholesterol is by drugs.
#8 there aren’t any more studies saying milk is good for than those saying milk is bad for you
if you’re going to add comments in a medical vein, why don’t you bother doing real research, instead of listening to your vegan media as if it is real research. It spins a story just as much as any media does.
— LizM, PHD studentI am a doctor and I believed none of these myths. Does the article you cite give examples of doctors who believe these myths? If not, then your headline is misleading.
— House WhispererAs another member of the medical profession, I too found the publication of this article in such a respectable newspaper inexcusable without posting data indicating what percentage of physicians believed these myths.
If the authors did not supply this data to the newspaper, it is both the fault of the authors for sloppy work, as well as the newspaper for printing the report.
The authors should print an erratum with the requested percentages.
— MDk2, yes, thank goodness a heart bypass is normal medicine that can save many, many lives. And I don;t know anyone who thinks that a vegan diet is unreasonable, just different and perhaps not to their liking.
But let’s keep piling on with irrelevant axes to grind.
— hankBravo for a cogent description of some facts surrounding these prevalent self-perpetuating biological myths. The likely origin of the 8 glasses of water per day was especially useful; I have sought that out unsuccessfully for a number of years. This article will greatly simplify my continuing task of infusing some degree of medical science into my delightful but frequently misinformed flock. I am also, however, a bit skeptical about how many of my colleagues truly subscribed to these myths, as the BMJ article is said to assert.
— Dr Steven KannerMyth #11. Vegans are physically healthier than the general meat-eating population.
— MattWhat about the repeated Thanksgiving stories citing the use of tryptophan in turkey tranquilizers that was then passed to humans? Also, your hair shaving point makes no sense. If the hair that grows back is less tapered and darker, than it is different from the original. If I have blonde arm hair, shave it, and it grows back black, that is different. This is wishy washy at best…
— Patrick WardThese myths are amusing and essentially harmless. Too bad more attention hasn’t been paid to the many medical myths that cost billions (like the alleged efficacy of over-the-counter cold remedies) or are dangerous (like having post-menopausal women take estrogen is a good idea).
— rwIf you’re over 21 and develop diabetes it must be type 2.
— tThis item should not have been published.
1. Cell phones. While the effect of cell phones on medical equipment is controversial, it is not a “myth”: it’s a controversy. There is an effect sometimes especially at low distance; then there’s a discussion of policy trade-offs — how much risk for what benefit and how to make an enforceable simple policy.
Some research by Dutch scientists into mobile phones and hospital equipment was published here: http://ccforum.com/content/11/5/R98
and reported in the New Scientist in September 2007 here:
http://technology.newscientist.com/channel/tech/mg19526214.000- cellphones-are-an-increasing-danger-in-hospitals.html
2. Reading in dim light may affect ocular development and be myopia-potentiating; the popular opinion is more certain than the science. That does not make it a “myth.” (Compare to the absurd, zero-data view harking back to William James’ speculation about the 10% of brain in use.)
— David GrosofHow did they leave out the one myth that causes so much grief - the ideal weight vs. height chart, which has no medical basis. Even most doctors use that thing. Insurance companies use it. Weight loss scheme companies use it. In reality it has nothing to do with a persons health.
— Tony T.Thank you for an article that was fun.
— ZaneyHowever, since physicians are just human beings, is it really noteworthy that they believe in some myths? Should they be myth-free simply by virtue of their M.D.? And, does this mythology apply to others in the health field who converse with patients as much or more than busy M.D.s?
While the study may show no effect of cell phones “in the normal way” provided no meaningful interference, 1.2% of the times, this is by no means inconsequential.
1. First, ask any audio or video technician who records events about cell phone interference… they will tell you that it is not only the ringing of a cell phone that interferes with a recording… before a cellphone rings a technician can absolutely hear a hum interference that is caused when a phone connects to the network just prior to ringing. Sprint/Nextel - the “click to talk” walkie talkie mode in particular causes the most interference on sets or live recording programs. While this doesn’t mean that “random” electromagnetic interference will cause clinically relevant problems, it does mean that systems that rely on transmitting and receiving wireless information, or systems that do utilize a magnetic device for operation and are sensitive to low levels of interference can be affected.
2. 1.2% does not equate to “acceptable” standards… if you were to talk about “network reliability” from your internet provider to your business, most businesses that operate financial transactions require 99.9% or greater uptime… meaning that financial requirements already beat that 1.2% margin of errors. But many businesses require 99.99% or greater uptime, because 99% uptime of business during standard 9-5 business hours translates into 16+ hours of downtime a year… that’s 2 out of 200 business days down… whereas 99.99% uptime translates into 1.6 hours of downtime a year.
In a hospital setting, obviously 2 days worth of downtime, or interference, a year can have an impact on some departments. But not on all… so it is best to determine what is mission critical and treat it as such.
Many if not most systems subject to electromagnetic interference in a research setting is isolated in a Faraday cage to protect against interference… and rather than blindly following or rejecting based on small, random reports or “conventional wisdom” hospitals need to evaluate the risk on a per-machine basis with the manufacturers and ensure that proper installation and configuration is addressed.
— MikeAt age 65, a woman has the greatest life expectancy if she is FORTY POUNDS HEAVIER than her “ideal weight”, according to the height/weight tables.
Neither is diabetes caused by being fat. It’s caused by defective mitochondrial RNA, as we’ve known for almost 20 years.
Ah, but many doctors still think that gout is caused by eating rich foods (disproven in the 1940s), and ulcers are caused by too much stomach acid (disproven in the 1980s). They’ll figure out that diabetes causes obesity, not the other way around, in another century or three….
— Paul Ding