We Asked Doctors What Our Dumbest Health Beliefs Are

Even reasonably well informed patients walk into doctor's offices every day with assumptions that are 100 percent false. We asked three health care providers on the front lines to share the most common misconceptions that drive them nuts—and to shed light on the truth.

Green mucus means you need antibiotics. 
From amoxicillin to Z-packs, antibiotics rank as one of medicine's greatest discoveries—but as the name implies, they only work against illnesses caused by bacteria. Meanwhile, viruses deserve the credit for colds, flu, and most sinus infections, says Myers R. Hurt III, a family doctor at Diamond Physicians in Frisco, Texas.

Contrary to the belief of many patients and even some doctors, Hurt says, the color of the stuff oozing from your nostrils and clogging up your coughs has more to do with where you are in the course of your illness than what's causing it.

When your body fights any kind of foreign invader, your white blood cells produce iron-containing enzymes—that's what gives your snot its grassy tint instead of a sunnier yellow glow. Meanwhile, dehydration intensifies the color.

There's some evidence that for the super-sick—say, people recovering from heart surgery or with chronic obstructive pulmonary disease—mucus color does signal flare-ups worthy of medical attention. But for those of us just dealing with a run-of-the-mill cold or respiratory infection, studies have found zero link between the shade of your sputum and the chances that antibiotics will make you better.

If antibiotics won't work, anyway, it's not wise to take or demand them. Besides contributing to the worldwide rise of drug-resistant superbugs, you risk developing fun complications like diarrhea and yeast infections, Hurt says. And anyway, snot remains stubbornly difficult to color-code. Belgian researchers found even microbiologists and pulmonologists agreed on sputum hue less than half the time—meaning your diagnosis-by-loogie is likely even less accurate.

Living wills are just for old people. 
If you're young and (relatively) healthy, you might never have considered what'll happen if your heart stops or whether you'd want to be hooked up to a breathing tube. But now—when you're thinking clearly and can communicate openly—is actually the best time to contemplate, Hurt says.

Advance directives spell out your wishes on issues like whether you want to be resuscitated, given a ventilator or feeding, or donate your organs or tissues when you die. You can also name a health care proxy, or a person you trust to make decisions when you can't.

Grim topics, sure—but accidents and sudden illnesses happen to people of all ages. Thinking about them now will mean your wishes will be honored in the unfortunate event they happen to you. The proper forms of these documents vary by state, so talk with your doctor or an attorney about having the proper paperwork on file with your medical chart, Hurt says.

You can split pills to save cash on drugs. 
Call this one a half-truth. The baffling economics of medications means sometimes one 400 mg tablet costs less than two 200 mg doses. In some cases, the medical math is straightforward enough that you can simply buy the bigger pill and cut it in half, Blais says. For instance, one study showed breaking statin drugs into two parts didn't diminish their effectiveness for controlling cholesterol.

In fact, your pharmacist might even suggest splitting pills as a cost-saving measure. Pills that are safe to split will say so on the label, in the part marked "How Supplied." And the tablet itself will probably be scored right at the spot you're supposed to divide it.

But for certain medications—say, capsules, or those covered with a coating designed to dissolve in your digestive system—splitting can cause major headaches. You might mess up the dosage, increase your risk of side effects, or render your drug completely ineffective, says Jeremy Blais, a pharmacy supervisor at CVS Health. Oh, and definitely don't split the doctor-recommended dosage in two in order to make your prescription last extra long. That's a surefire way to make sure your health problems don't improve.

Everyone should take loads of Vitamin D. 
Thanks to modern inventions like electricity and sunscreen, we humans get a lot less sun exposure than we used to. That's led to what some experts have called a near-epidemic of vitamin D deficiency. In fact, more than three-fourths of American walk around that way, says Rachel Carlton Abrams, a board-certified family physician and author of BodyWise.

Low levels have been linked to conditions from bone loss to cardiovascular disease to cancer. But too much can pose problems too, says Abrams, who's had patients tell her they're taking 15,000 IUs per day (that's far above the government-recommended daily upper limit of 4,000 IUs). Unlike vitamin C, which is water-soluble, vitamin D is stored in our fat, Abrams says. So you don't just pee out extra—your body hangs onto it, potentially causing damage to your heart, blood vessels and kidneys over time.

If you're going to pop a D pill, stick closer to 1,000 or 2,000-mg doses. Better yet, ask your doctor for a blood test, Abrams recommends. There's some debate on optimal levels—some, including the Institute of Medicine, say 20 nanograms per milliliter of blood marks the cutoff, while others place it higher, at 40 or 50. But your doc can help you decide on an appropriate target and a supplement strategy to reach it.

The flu shot gives you the flu. 
Sounds plausible—but in fact, it's biologically impossible, according to the Centers for Disease Control and Prevention. Flu shots contain either inactivated verses or no viruses at all, meaning they can't cause the flu illness.

Sure, you might get a little achy and sniffly shortly soon after your vaccination. That's a sign your body's reacting to the antigen, building immunity. The full-fledged flu—the disease you're creating antibodies against—is a serious illness that can put you out of commission completely for a week or longer, Blais says.

It's also possible to catch the flu or a flu-like illness even though you're vaccinated. Every year, scientists predict which strains of influenza will circulate, so they can distribute vaccines before the first bug hits. This year, shots reduced the risk of developing flu by about 43 percent, the CDC announced in February.

That means a lot of people still got sick, and while it's a bummer if you happen to be among them, you're still better off having gotten the shot. Flu cases are typically milder in the immunized, Blais says. If past years with similar stats are a guide, by the end of this season the shots will have warded off 5.6 million cases of illness, 2.7 million doctor's visits, and more than 61,000 hospitalizations. (And, by the way, it's not too late to take your jab this year—flu season technically lasts until April, Blais says.)

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