Increased Vitamin C consumption is associated with reduced risk for most types of cancer. Multiple case-control studies have investigated the role of Vitamin C in cancer prevention, and most have shown that higher intakes of Vitamin C are associated with decreased incidence of cancers of the mouth, throat and vocal chords, esophagus, stomach, colon-rectum, and lung. One study that followed 870 men over a period of 25 years found that those who consumed more than 83 mg. of Vitamin C daily experienced a striking 64% reduction in lung cancer compared with those who consumed less than 63 mg. per day.

Laboratory experiments indicate that Vitamin C inhibits the formation of carcinogenic compounds in the stomach, a finding supported in observational studies that have found increased dietary Vitamin C intake to be associated with decreased risk of stomach cancer.

Studies conducted by Linus Pauling (Nobel Prize winning scientist, pioneer in the fields of quantum chemistry, molecular biology, and orthomolecular medicine) suggest that very large doses of Vitamin C (10 grams/day intravenously for ten days followed by at least 10 grams/day orally indefinitely) are helpful in increasing the survival time and improving the quality of life of terminal cancer patients.

Intravenous (IV) administration of Vitamin C can result in much higher blood levels of Vitamin C than oral administration, and Vitamin C levels that are toxic to cancer cells in culture can be achieved in humans only with intravenous but not oral administration of Vitamin C. The Angeles Functional Oncology treatment program provides IV-delivery of Vitamin C in concentrated dosage, ranging from 40 to 70 grams per day.