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Why We Believe Medical Myths

Why do we keep clinging to myths, even when research or other facts tell us the myths aren’t true? That’s the question posed by Newsweek’s Sarah Kliff, discussing a new book put out by Vreeman and Carroll, who blow away 66 new medical myths in their new book, Don’t Swallow Your Gum!

The research offers only a few answers as to why we keep believing things like we must drink 8 glasses of water a day (myth) and the belief that vitamin C helps cure the common cold (myth):

The body of research on belief formation is relatively sparse. One expert in the field, York University psychologist James Alcock, admits that it’s difficult to trace where beliefs start.

“Even as individuals we usually can’t explain where beliefs come from,” says Alcock, who is currently at work on a book about the psychology of belief. “Why should you drink eight glasses of water? People will say they heard it somewhere. Sometimes it’s impossible to trace the source, but it just gets repeated over and over.”

Some myths begin with a kernel of truth that gets misinterpreted, like the eight-glass theory. In 1945, the Food and Nutrition Board of the National Research Council stated that adults should take in about 2.5 liters of water a day and that most of this is contained in prepared foods. Ignore that last part of the recommendation and you’ve got the eight-glass mandate.[…]

So why do we do it? Something called “illusory correlation” may play a role:

Once we believe something, whether it’s truth or myth, we begin to see confirmation in the world around us. In psychology, Alcock explains, this is known as an illusory correlation: making connections between particular events that line up with our beliefs about the world.

I also think this ties in with something called “confirmation bias,” which suggests we only seek out information (or interpret information we find) that confirms our existing preconceptions about something. So if we hear “Drinking 8 glasses of water a day is a myth,” we’ll go look for something online that tells us otherwise (such as this article on the Mayo Clinic’s website that repeats the 8 glasses of water a day myth as an acceptable medical recommendation, despite admitting that the approach “isn’t supported by scientific evidence.” Which kind of begs the question — why list it on your medical website if there’s no evidence to support it?).

Getting back to Alcock’s explanation:

“We can become attached to beliefs that seem to serve a function for us,” Alcock explains, “and we don’t like to give them up even if they’re false because they seem too true to be false.” This is especially true when we get information from a trusted source. Since medical myths usually come from parents, doctors and media, it’s no surprise they’re particularly robust.

A while back, Alcock did an experiment with his students in illusory correlations. He told them all that redheads were particularly erratic drivers and to watch out on the road for them. Sure enough, his students came back reporting all sorts of stories of redheads gone wild on the road.

Alcock’s pointing out that once this misinformation is out there, it’s very difficult to change. Myths take on a life of their own and enter into the “common wisdom” of society.

What about the myth that sugar intake causes symptoms of ADHD?

Those illusory correlations seem particularly strong with one of the more controversial myths that Vreeman and Carroll debunked that sugar causes hyperactivity in children (it doesn’t). There’s a slew of double-blinded, randomized trials that have shown no connection between sugar consumption and a child’s increase in energy.

“For that one, anecdote seems to trump science,” says Carroll. “They don’t care how many good studies are out there, they’ve seen it happen with their child so they know it must be true.” Carroll suspects that parents will often associate situations with sugar a birthday party, for example with hyperactivity and immediately identify sugar as the culprit, rather than considering the other factors that could cause a burst in energy.

Again, it doesn’t help when websites such as WebMD suggest that “a child may become more active due to an adrenaline rush produced by this blood sugar spike” when answering the question “Does sugar cause symptoms of ADHD.” The real answer is simply, “No, there’s no proof that sugar is connected to symptoms of ADHD in children.” Instead of that being the first sentence in the answer, it’s the last sentence, clouding the clarity of our existing knowledge (and the actual answer).

What can be done about all of these medical myths that seem to continue to float around?

Medical myths usually stick around because no one’s on a public-health crusade to set the record straight. Of all the battles to pick in health care, chances are convincing Americans that they don’t need to have eight glasses of water is nowhere near a top priority.

True. Although a search of information on the web about the “8 glasses of water a day” myth seems to be busted by every mainstream website in the search results. That’s because when a website can write a news article that “busts” a myth, it can be very newsworthy in itself.

So one of the ways we can combat such myths isn’t by a public health crusade, per se’. It’s by simply reporting on studies as they are published, which can by itself provide some counterbalance to the myth.

Read the full article: Why We Cling to Outdated Medical Myths

Why We Believe Medical Myths

John M. Grohol, Psy.D.

Dr. John Grohol is the founder of Psych Central. He is a psychologist, author, researcher, and expert in mental health online, and has been writing about online behavior, mental health and psychology issues since 1995. Dr. Grohol has a Master's degree and doctorate in clinical psychology from Nova Southeastern University. Dr. Grohol sits on the editorial board of the journal Computers in Human Behavior and is a founding board member of the Society for Participatory Medicine. You can learn more about Dr. John Grohol here.

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APA Reference
Grohol, J. (2018). Why We Believe Medical Myths. Psych Central. Retrieved on September 29, 2020, from
Scientifically Reviewed
Last updated: 8 Jul 2018 (Originally: 30 May 2009)
Last reviewed: By a member of our scientific advisory board on 8 Jul 2018
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