For the interventions tested, in the populations described, there is scant evidence that vitamin C or vitamin E beneficially affects survival. Similarly, for the interventions tested, in the populations described, there are no results suggesting a benefit for the prevention of new tumors, which reach statistical significance with the exception of prostate cancer in subjects treated with alpha-tocopherol. One trial reported a benefit of a megadose vitamin therapy on the development of new tumors in patients with bladder cancer. However, the ability to infer from this finding is limited because the multi-component intervention limits our ability to attribute the reported efficacy to any particular component.
For the outcome for colonic polyps, four trials focusing on secondary polyp recurrence could be pooled for analysis and none used vitamins C or E as a single intervention. The combination of vitamins C and E was not clinically superior to placebo in secondary prevention. The combination of vitamins C and E with beta-carotene or vitamin A did show a trend favoring a reduction in polyp recurrence, but this finding was not statistically significant.
The systematic review of the literature does not support the hypothesis that the use of supplements of vitamin C or E or coenzyme Q10 generally help prevent and/or treat cancer. There were isolated findings of benefit, which require confirmation.