Is there a role for oral or intravenous ascorbate (vitamin C) treatment for patients with cancer? A systematic review

Background: Despite a lack of high quality clinical data supporting its use,thousands of patients choose to pay for intravenous (IV) ascorbate (vitamin C) in the belief that it synergizes the anti-cancer effects of chemotherapy and reduces its toxicity. Methods: A formal systematic review of human interventional and observational studies of both oral and IV ascorbate treatment and their anti-tumor effects in cancer patients was performed. Two reviewers independently screened all abstracts and full text articles. Data collection and quality assessment of studies was performed using the Jadad and Newcastle-Ottawa scales. Results: Of 677 records initially identified, 58 full text articles were screened and 34 studies included. We identified 5 randomised controlled trials (n= 322), 12 phase I/II trials (n= 283), 6 observational studies (n= 8558) and 11 case reports (n= 264). None of these trials demonstrated any statistically significant validated anti-tumour effect of ascorbate. Evidence presented for the anti-tumour effect of ascorbate was anecdotal, observational and from uncontrolled studies. Evidence for the safety of ascorbate was shown in small single-arm trials (n=86). Case reports of significant adverse effects were found (n=6). Quality assessment of the published studies showed them to be generally of low quality. Conclusions: There is no high quality evidence to suggest that either oral or IV ascorbate supplementation in cancer patients has either anti-tumour effects or that it reduces the side effects of chemotherapy. Limited single-arm evidence suggests that IV ascorbate may be safe. However, given the high financial and time costs to patients and their families of IV ascorbate, high quality placebo-controlled trials are needed.