Since 1970, when Nobel laureate Linus Pauling first touted it as a cold remedy, vitamin C has been passionately championedand reviled. Some studies support it, but others cast doubt. According to the latest studies, it turns out C can't stave off colds. A 2007 review of 30 trials published in the Chochrane Database of Systematic Reviews showed that vitamin C is largely ineffective in cold prevention, and its ability to relieve cold symptoms is basically insignificant. But the vitamin does help to cut colds in people under extreme stress, such as skiers, soldiers, and marathon runners. "Vitamin C is not a miracle cure, but it makes colds milder," says Mary Hardy, MD, medical director of the Integrative Medicine Program at Cedars-Sinai Medical Center in Los Angeles.
Dosage: Take 500 milligrams or more four times a day, from the moment you realize you're coming down with a cold until you feel like yourself again.
Caveats: Loading up on more than 5,000 milligrams of vitamin C a day is useless at best, because your body cannot absorb that much; at worst, megadosing is harmful because it can upset your stomach.