Health myths can be as stubborn as ink stains. Passed down from generation to generation or created anew, they refuse to fade away.
We hear them so often we just assume they're true. Some myths have roots in Old English lore, some in one single newspaper quote blown out of proportion. Others are based on nothing more than instinct and emotion.
However, not all of these beliefs are wholly untrue. In many cases, science reinforces what our parents and grandparents have been preaching. Here is the truth behind a few of the most enduring.
Eating an apple every day will prevent illness.
This phrase most likely comes from an Old English verse: "Ate an apfel/avore gwain bed/makes the doctor/beg his bread."
Though they're far from being a wonder drug, apples have plenty of benefits. In 1989, researchers in Japan found that people who ate three or more apples a day were less likely to develop high blood pressure as they got older.
Apples contain boron, a trace mineral that increases calcium absorption, which also may aid in preventing osteoporosis. They also contain fiber, which can help lower cholesterol.
If you swallow chewing gum, it takes seven years to digest.
Forget that scary vision of a wad of gum bouncing around in your stomach like a basketball in an empty gymnasium. While it's true that gum is not digestible, it does not linger in the stomach. Like bran and the skins of many fruits and vegetables, chewing gum is a fiber. Fiber, of course, is that wonderful substance that helps push food rapidly through the body.
"Gum passes right on through the intestines. It doesn't stick just because it's sticky," says Susan Mikolaitis, a registered dietitian with Loyola University Medical Center.
This myth's source is unknown, but Mikolaitis guesses it comes from years of parents trying to keep their children from swallowing gum. "It's not seen as socially the right thing to do," she says. "Parents fear children may choke on it, but nothing bad will happen to your digestive tract."
Eating spicy food in the evening will give you bad dreams.
Enchiladas and Thai green curry most likely do not encourage the nocturnal bogeyman. The main reason people think spicy foods create bad dreams is because these foods can create discomfort, which leads to restless sleep. Another possibility is that spicy foods are often eaten with alcohol, which is known to cause increased intensity of dreams in the last half of the night.
Peppers and spices derived from peppers can stimulate more gastric acid and relax the valve at the top of your stomach, which can allow food to work its way up the esophagus when you lie down, says Dr. Virgil Wooten of the Sleep Disorders Clinic at Eastern Virginia Medical School and spokesman for the American Sleep Disorders Association.
"I have patients say if they eat certain foods, they have more nightmares, and I don't really know what to make of that," he says. "Despite the lack of evidence, I suppose it's possible because there are medications doctors prescribe that cause more dreams and nightmares in some patients."
The best advice is to be wary of the time you eat spicy foods and drink alcohol; turbulent stomach storms will be noticed more if you eat or drink closer than three to four hours before bedtime. Milk may calm those dreams. It's a source of tryptophan, an amino acid that helps the brain produce serotonin, a chemical that turns on the brain's sleep switch.
Taking extra vitamin C will prevent colds.
In the early 1970s, Nobel Prize-winning scientist Linus Pauling began to tout vitamin C as a preventive measure against cancer and the common cold -- and one of the most argued medical myths of this century was born.
Since then, researchers have conducted study after study on this subject, and they agree only on one thing: The evidence is less than overwhelming that vitamin C prevents colds or reduces their symptoms.
In 1975, the Journal of the American Medical Association published a review of 14 studies about vitamin C, showing that people who take 1,000 or more milligrams of vitamin C each day had fewer and shorter colds than those who didn't -- but only shorter by one-tenth of one day.
In 1987, researchers at the University of Wisconsin Medical School found that people who took vitamin C supplements had milder cold symptoms that disappeared, on average, five days sooner than those of people who didn't take the vitamin.
More recently, a study at the University of Helsinki in Finland showed that vitamin C supplements helped prevent colds in people who normally had a low dietary intake of vitamin C.
"There's been some suggestion that vitamin C slightly alleviates symptoms after you have a cold, but I don't think there's much evidence it has beneficial health effects," says Dr. Walter Willett, professor of epidemiology and nutrition at Harvard University's School of Public Health.
Although too much of some vitamin supplements can actually be harmful for you, extra doses of vitamin C don't pose a serious health risk. Dr. Willett says the body sheds unneeded vitamin C through urination.
Cracking your knuckles will give you arthritis.
Knuckle cracking might slightly weaken a person's grip, but it's not enough to alarm doctors.
"If there were a striking relationship, it would have been recognized by now," says Dr. Doyt Conn, senior vice president for medical affairs with the Arthritis Foundation.
It's no wonder this myth exists: Knuckle cracking sounds awful, like a twig snapping or a bone breaking. Actually, it's nothing more than an air bubble popping in the synovial fluid of your joints. The sound is relatively loud because this fluid is thick, like honey.
About 25 percent of people in the United States are chronic crackers.