Despite what you may have heard, drinking eight glasses of water a day isn't the key to good health. Also, neglecting to wear a coat on a cold day won't make you sick. And — you might want to sit down for this — pregnancy doesn't last nine months.
Health-related myths are often repeated as fact, even though any diligent Google search will reveal the truth behind these fallacies. Here are 26 of the most common medical myths, debunked.
Myth: Vaccines can cause the flu (and autism).
Although the body can develop a low-grade fever in response to any vaccine, rumors that a flu shot can cause the flu are "an outright lie," said Dr. Rachel Vreeman, co-author of "Don't Swallow Your Gum! Myths, Half-Truths, and Outright Lies about Your Body and Health (opens in new tab)" (St. Martin's Griffin, 2009).
The flu shot does contain dead flu viruses, but they are, well, dead. "A dead virus cannot be resurrected to cause the flu," Vreeman told Live Science in 2010. As for vaccines causing autism, this myth was started in 1998with an article in the journal The Lancet. In the study, the parents of eight (yes, only eight) children with autism said they believed their children acquired the condition after they received a vaccination against measles, mumps and rubella (the MMR vaccine). Since then, rumors have run rampant despite the results of many studies. For example, a 2002 study in The New England Journal of Medicine of 530,000 (yes, a whopping 530,000) children found no link between vaccinations and the risk of a child developing autism.
Unfortunately, the endurance of this myth continues to eat up time and funding dollars that could be used to make advances in autism, rather than proving, over and over again, that vaccinations do not cause the condition, said Vreeman, who also researches pediatric conditions.
Myth: Supplements always make you healthier.
Vitamin supplements may be not only ineffectual but even dangerous, studies have shown. For example, a study published in 2016 showed that some older women who take calcium supplements may face an increased risk of dementia. And in a huge review of 20 years of supplement research published in 2015, researchers found that taking high doses of vitamins may be linked with an increased risk of cancer.
Aside from these possible long-term risks, reports have suggested that supplements can cause damage in the short term too. A report published in 2016 found that a man in Pennsylvania who took Ayurvedic herbal supplement developed lead poisoning. Another report, also published in 2016, showed that a 4-year-old boy in England went to the ER after taking a slew of "natural" supplements, and developing a condition called vitamin D toxicity.
"The FDA does not require supplements to be regulated in the same way that drugs are, which can be a real problem," Vreeman said in 2010. As a result, the safety of many supplements has not been rigorously studied. Furthermore, supplement bottles can sport unsubstantiated claims and even make errors in dosage recommendations, she said.
It's a better idea to get your vitamins and other nutrients from eating real food, rather than taking a pill, she said.
"A vitamin pill is not the answer," Vreeman said. "Eating more healthily in general is the answer."
Myth: Cold weather makes you sick.
"This myth is common around the world, but it is just not true," Vreeman told Live Science. Studies have shown we may feel more cold symptoms — real or imaginary — when we are chilled (after all, a cold is called a "cold" for a reason), but the temperature itself does not make us more susceptible to viruses. This has been known since at least 1968, when a study in The New England Journal of Medicine showed what happened when researchers exposed chilly people to the rhinovirus (one cause of the common cold).
It turned out that whether they were shivering in a frigid room or in an icy bath, people were no more likely to get sick after sniffing cold germs than they were at more comfortable temperatures.
Vreeman said that cold air also does not make a difference in people's recovery time from a cold. In fact, although the research is in its early stages, "it is possible that being exposed to cold may even help your body in some way," she said.
However, its unclear how chilly conditions might affect the germs themselves. Research has shown that two common causes of colds — rhinoviruses and coronaviruses — may thrive at colder temperatures, and that the flu may spread most effectively under cold, dry conditions.
Some scientists speculate that colds are more common in cooler months because people stay indoors more, interacting more closely with one another and giving germs more opportunities to spread.
Myth: We use only 10 percent of our brains.
Motivational speakers and other self-help gurus have been promoting this one since as early as 1907, as a way to encourage people to tap into some latent capacity, explained Vreeman and the co-author of her book, Dr. Aaron Carroll, both of the Indiana University School of Medicine, write in the book. But these people were not basing the proclamation on sound science.
Today, scientists can look at any brain scan, measuring activity at any given time, and have a big laugh at this myth. "You just don't see big dormant areas," Vreeman said. The idea lingers in popular culture because "we want to think we haven't reached our full potential," Vreeman said.
Myth: Sugar turns kids into little monsters.
It can be hard to find a parent who does not believe this, Vreeman said. "But it is in their heads." In one particularly clever study among a slew of studies finding sugar's nil effect on unruliness, kids were given Kool-Aid sweetened with aspartame, a compound that contains no sugar. Researchers told half of the parents the Kool-Aid contained sugar, and told the other half the truth.
The parents in the study who thought their kids were riding a sugar high reported their children were uncontrollable and overactive. But a sensor on the kids' wrists that measured activity level said the opposite: The kids were actually acting subdued. The study was published in the Journal of Abnormal Child Psychology in 1994.
Sugar is often given at times when the rules are loosened and there are lots of other kids around, like birthday parties and holidays, Carroll told Live Science. These factors may be behind the myth's persistence in popular culture, he said.
Myth: You need to stay awake if you've had a concussion.
Anyone who may have a concussion should seek medical attention, but the condition is rarely severe or life-threatening. Warnings that people need to stay awake after incurring a concussion most likely grew out of a misunderstanding about a particular type of head injury — one that involves brain bleeding and that causes people to have a "lucid period," followed by a coma or even death. But this is very uncommon and doesn't pertain to people with normal concussions, Vreeman said.
"If you've been evaluated by a doctor, and he has said that you have a mild regular concussion, you don't need to worry that someone has to wake you up every hour," she said.
Myth: Chewing gum stays in your stomach for 7 years.
Although it is true that many of the ingredients in gum — such as elastomers, resins and waxes — are indigestible, that does not mean they hang out in your guts for seven years. Plenty of what you eat — even things you are recommended to eat, such as fiber — is indigestible. But the digestive system is a robust piece of organic machinery, and anything it can't absorb, it moves along. Despite the stickiness and strange consistency of gum, "it passes right through your digestive tract and into the toilet," Vreeman explained.
Myth: Reading in the dark or sitting too close to the TV ruins your eyesight.
Dim light — or alternatively, staring into the multicolored tube at close range — can undoubtedly make your eyes work so hard they hurt. But there is no evidence that these practices cause long-term damage, Vreeman said. The TV myth may have started in the 1960s, and at that time, it may have been true. Some early color TV sets emitted high amounts of radiation that could have caused eye damage, but this problem has long been remedied, and today's TV and computer monitors are relatively safe, she said.
If you or your child tend to sit so close to the computer or TV that it hurts the eyes, it may be a good idea to get checked for nearsightedness. However, sitting too close does not create a need for glasses even if getting glasses can remedy the habit.
Myth: You should drink at least 8 glasses of water a day.
"In general, we are not all walking around in a dehydrated state," Vreeman said, adding that our bodies are very good at regulating our fluid levels. The eight-glasses-a-day myth likely started in 1945, when the Food and Nutrition Board of the National Research Council said adults should take in about 2.5 liters of water a day (equivalent to about eight glasses, or two-thirds of a gallon). Although most media outlets reported that as fact and stopped there, the council actually went on to explain that most of the 2.5 liters comes from food. According to Vreeman, the recommendation should be amended to the following: Drink or eat about eight glasses of fluid a day.
Myth: You should wait an hour after eating before you go swimming.
This myth has ruined many summer afternoons, forcing young and old to swelter in the heat while cool waters beckoned, all because they were careless enough to down a PB&J. Let the ban be lifted: There is no special reason not to swim after eating, Vreeman said.
It's true that any type of vigorous exercise can be uncomfortable (although not dangerous) after an overwhelming feast. But for most of us whose waterfront dining experience includes sand-dusted chips and soggy sandwiches, that is hardly a concern. And cramps can happen anytime, whether you've eaten or not. If you are swimming in waters so rough that a charley horse will mean the death of you, you should probably swim elsewhere. Just don't forget the picnic!