It won’t. Vitamin C has long had a reputation for helping prevent colds and people often gulp megadoses when they feel cold symptoms coming on, but clinical studies have shown no effect for vitamin C in cold prevention in normal situations. However, research has shown that doses of 200 mg or greater (more than twice the 60-75 mg current recommended dietary intake for adults) may help reduce the duration of colds slightly. The likelihood of success seems to vary with the person—some people improve after taking vitamin C supplements, others don’t. Try it and see for yourself, but don’t exceed 2,000 mg per day. More than this can cause an upset stomach
Similarly, zinc lozenges may also help cut the number of days you’re sick. In a study in the Journal of Infectious Diseases, adults who took zinc in lozenge form (13.3 mg every 2 to 3 hours for as long as their cold lasted) within a day of noticing the telltale signs kicked the bug about 3 days sooner than those who got a placebo. Though that dose exceeds the recommended daily max of 40 mg, it’s safe for a 3- to 5-day period, says study author Ananda Prasad, M.D., Ph.D. Scientists think zinc binds to cell receptors in the mouth and throat, blocking the cold virus from attaching and spreading. Zinc comes in many forms, but only lozenges have been shown to be effective. Skip nasal sprays and swabs: they may damage your sense of smell. And zinc from food (beef, dark poultry meat, shellfish) probably won’t help, either, as you can’t get enough that way.