The common cold, or simply the cold, is a viral infectious disease of the upper respiratory tract. The cold is indeed common, and is a significant cause for absences from work and school. Even before the discovery of vitamin C, folklore had it that certain fruits were effective in both preventing and treating the cold. After scientific identification of vitamin C in the early part of the 20th century, research began into the possible effects of the vitamin against the common cold. Vitamin C does not decrease the frequency of colds in the general population, but it has halved the frequency of colds in people under heavy short-term physical stress. There is no effect of taking vitamin C in doses up to 8 grams per day after a cold has already begun. Source: Wikipedia (en)