The connection between vitamin C and the common cold has been a source of controversy for decades. Many people are convinced that taking large quantities of vitamin C will prevent colds or relieve cold symptoms. To test this common cold myth, several large–scale, controlled research studies involving children and adults were conducted.

Vitamin C and the common cold: Research results
To date, no conclusive data have shown that large doses of vitamin C prevent colds.

For people who take vitamin C every day, it may reduce the severity or duration of cold symptoms, but there is no clear evidence supporting this. Once symptoms of the common cold begin, taking vitamin C has not shown any benefit in reducing the severity or duration of cold symptoms.

Taking vitamin C for common cold prevention could provide some benefit for people exposed to brief episodes of intense exercise or extreme cold–weather environments.

Vitamin C and the common cold: Side effects
Taking vitamin C over long periods of time in large amounts may be harmful.

Too much vitamin C can cause severe diarrhea, a particular danger for elderly people and small children.

Source: cold.emedtv.com