Why We Cling to Outdated Medical Myths

Rachel Vreeman and Aaron Carroll weren't looking to start a controversy. They're both pediatricians at Indiana University who, as a side project to their day jobs, put together a study on a few medical myths that many doctors believe. The results weren't exactly earth-shattering: they revealed that you don't actually need to drink eight glasses of water and nails do not continue to grow after death. And the research definitely wasn't new. "We looked through old research and basically put it all together," explains Vreeman.

But from the reactions that Vreeman and Carroll got, you'd think they were questioning the very flatness of the earth. They received hundreds of e-mails from strangers and dozens of media requests. One particularly disquieted man repeatedly called their office, irate over their discrediting of the eight-glass myth. He was so threatening and abusive that their administrative staff filed a restraining order. "A lot of people were incredibly upset to think that we would question the fact that you need eight glasses of water," says Vreeman. "Nine studies from the physiology literature have suggested we get enough water from other things we drink, yet many people feel very strongly about water."

Now, the authors are back with Don't Swallow Your Gum! (Griffin Original), a book of medical myths and half-truths that will be published next week. Among the 66 myths, there's something to surprise everyone: that, despite what Mom told us, vitamin C does not cure a cold and even the highest SPF sunscreen will not prevent all sunburns. But what's more surprising than the myths they debunk, is how strongly their friends, colleagues and readers protested their research. Both Vreeman and Carroll have been repeatedly told they're incorrect, misinformed or flat-out wrong, that these are medical facts they're messing with. "It's not like we discovered something new, we just reviewed the literature," says Carroll. "But people still won't take it, it's like nothing would be enough to convince them otherwise."

Why do we believe and cling to these seemingly unimportant nuggets of information? Why is it so difficult for us to accept that reading in poor light won't ruin our eyesight and we don't actually need to drink eight glasses of water each day? Turns out, we're pretty likely to side with the things our doctors and parents have told us, myths we've seen reinforced with our own eyes, even when research tells us to believe otherwise. "People often take rumors or anecdotes as fact," says Vreeman. "We tend to give those things as much weight as we would a scientific study because they're connected to people in charge. We sometimes reason things out after the fact, come up with patterns to explain what we saw happen."

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. Others are couched in what seems like common sense, like the idea that reading in the dark is bad for the eyes. After all, our eyes do hurt after reading in the dark, so it makes sense to assume that some kind of damage is taking place.

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. "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.

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.

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. And if parents restrict their child's sugar intake because they're worried about hyperactivity, is it really all that bad? "For a lot of these things, the danger is negligible," says Carroll. "Let's say my mom knew reading in the dark was okay, so I would have gotten to read in bed more. But in the end, who really cares?"

There are, however, a few in their book though that the authors believe are worthy of a public-health crusade, particularly the supposed link between vaccines and autism that has not been validated by the research. Yet, believers may be inclined to overlook the science in favor of anecdotal evidence. (Think Jenny McCarthy's appearance on Oprah during which she describes watching her son, who has autism, get a vaccine and seeing the "soul gone from his eyes.") "People want to understand the world so they latch onto a reason," says Carroll. "We all know autism incidence is increasing and it's devastating. People looked for a pattern and when one emerged, they grabbed it." But it frustrates Carroll, a pediatrician by practice, that this medical myth not only misleads parents but also distracts the autism community. "Nothing would please me more than to find a cure for autism," he says. "Every dollar we sink into trying to combat these myths could be put towards research."

Will their book rid the world of medical myths and set the record straight? Carroll and Vreeman are realistic about their prospects and aren't on a crusade to end the eight-glass myth. It's instinctual to make sense of the patterns we see, to assign some kind of order to the mystifying connections that continually occur around us. Medical myths, however inaccurate they may be, will continue to persist because they make complicated material a little bit easier to wrap our heads around. So the authors don't expect their readers to come away form the book with a complete medical education, but rather a willingness to question their doctor's expertise. "I consider it a success if we got a few people to ask why," says Carroll. "If we empower patients to ask why, do we have to do this." It's a prescription that's probably good for any patient, regardless of how much water they're drinking.

Join the Discussion