Myth: Taking extra vitamin C helps prevent colds, the flu and other winter maladies.

Facts: Loading up on megadoses of vitamin C—say, between 1,000 and 5,000 milligrams (mg)—doesn’t do anything to prevent illness, says Adriane Fugh-Berman, M.D., an associate professor in the Department of Physiology and Biophysics at Georgetown University. An infusion of vitamin C also isn’t likely to make the duration of a cold any shorter, according to Gigi El-Bayoumi, M.D., associate professor of medicine at the George Washington School of Medicine and Health Sciences. During trials, only one in 10 people taking vitamin C found their colds cleared up faster. Vitamin C consumption often has a psychological effect, El-Bayoumi adds: People feel better because they are doing something about their illness.

Vitamin C is water-soluble and not considered harmful if you take more than the daily recommended dose of 100 mg, as long as you don’t exceed 2000 mg, says Larry Walker, Ph.D., director of the National Center for Natural Products Research at the University of Mississippi. If you take more vitamins than the body requires, they will simply be excreted in urine.

Still looking for the magic cure for a cold? The jury is still out about the effectiveness of the herbal supplement echinacea and zinc nasal sprays. And just because a substance is natural, that doesn’t mean it doesn’t have side effects, cautions El-Bayoumi. “When taken every two hours, zinc actually causes insomnia.” That is the dosage that should be used to make a very mild difference in a cold’s duration, she adds.

No drugs yet treat the viral infection that causes the common cold, says Walker. Over-the-counter drugs treat only the cold’s symptoms.

The best way to prevent illness is just what Mama told you: Eat a healthy diet of fruits and vegetables, get at least eight hours of sleep per night, avoid smoking and excess alcohol consumption, stay well hydrated, and wash your hands regularly, says El-Bayoumi. However, she adds that a hand sanitizer that contains at least 60 percent alcohol can cut down on colds and the flu by 50 percent.

Rebecca Kern is a writer based in Washington, D.C.