Vitamin C and Cancer

"The evidence is that five fruits and vegetables daily decreased risk of cancer in the gastrointestinal tract, intestinal tract and the respiratory tract," Mark Levine, who authored a report, told Reuters. "Is it because of the Vitamin C, or Vitamin C plus other components, or components in the fruits and vegetables independent of the Vitamin C? ... This we don't know," he said.

The reduced cancer risk was one of the criteria behind the researchers' proposal to double or triple the recommended daily ingestion of Vitamin C to 100—200 milligrams (mg) per day from 60. Since the last government review of the subject in 1989, a lot of research has become available to serve as a basis for a higher recommended dosage of Vitamin C, Levine said.

In the report, Levine and his colleagues said diets with 200 mg of Vitamin C from fruits and vegetables have been associated with lower cancer risk, especially cancers of the oral cavity, esophagus, stomach, colon and lungs. However, taking Vitamin C as a supplement in pill form did not decrease the incidence of colorectal adenoma and stomach cancer in experimental trials, the report said.

Vitamin C, or ascorbic acid, is not produced naturally by the body but is one of the 13 essential chemicals the body needs to function properly. The report's authors debunked a popular belief that large doses of Vitamin C—1 000 mg or more—can prevent or cure the common cold. "The patients who derived benefit, a slight reduction in cold incidence, were a small subset who were probably Vitamin C deficient," the report said. "Vitamin C doses of one gram or more could have adverse consequences in some people and physicians should counsel patients to avoid these doses," the report said, citing cases of diarrhea or abdominal bloating.