The relationship between vitamin C intake and susceptibility to the common cold has been the subject of much research. While some studies have suggested that high doses of vitamin C (e.g. 1-2 grams per day) may reduce the duration and severity of cold symptoms, other studies have found no significant effect. Some studies have also suggested that regular vitamin C supplementation may reduce the incidence of colds in certain populations, such as athletes and individuals exposed to extreme physical stress.
However, it should be noted that taking large doses of vitamin C (e.g. more than 2 grams per day) can have negative side effects. In particular, excessive vitamin C intake can cause gastrointestinal distress, including diarrhea, nausea, and abdominal cramps. In addition, some studies have suggested that excessive vitamin C intake may increase the risk of kidney stones, especially in individuals with a history of kidney stones or other kidney problems.
Therefore, while vitamin C may have some potential benefits for reducing the incidence and severity of the common cold, taking large doses of this vitamin can be dangerous and may cause negative side effects. It is generally recommended that individuals obtain their daily vitamin C intake from a balanced diet including fruits and vegetables, rather than from supplements or large doses of isolated vitamins.