Very high doses of vitamin C can cause gastrointestinal or kidney problems.
The überhealthy dont shrug off an impending coldthey attack it. Jenny Spring, 29, of Cambridge, Mass., takes a double shot of vitamin C and zinc at the first ominous sniffle or throat tickle that could be a sign of a cold or the flu. She sips the powdered drink mix Emergen-C (it packs 1,000 mg of vitamin C) once or twice a day, followed by a few blasts of Zicam, an over-the-counter zinc nasal spray. "Ive warded off coughs and colds long enough that I dont remember the last time I had one," she says.
Although vitamin C and zinc for cold prevention remain controversial, some studies show that C is especially helpful for people who are under extreme stress and that zinc can prevent viruses from multiplying. Experts say theres no harm in tryingand just believing these remedies work may help too.
Make C work for you: Neil Schachter, MD, director of respiratory care at Mt. Sinai Medical Center in New York City, suggests a more conservative amount of vitamin C (500 mg a day) at the first sign of a cold. And the Institute of Medicine advises drawing the line at 2,000 mg daily to avoid gastrointestinal or kidney problems. As for zinc, you might do better to opt for lozenges instead of up-the-nose remedies. In 2009, the U.S. Food and Drug Administration issued a warning that Zicam Cold Remedy nasal gel and nasal swabs were found to be associated with long-lasting or permanent loss of smell. Dr. Schachter suggests taking zinc lozenges several times a day when a cold starts.