L-ascorbic acid, commonly known as vitamin C, is an essential nutrient that must be present in the diet of human beings. Since the compound cannot be synthesized by the body it is critically important that the diet and other supplements fulfil the requirement. Being an electron donor, L-ascorbic acid is a potent antioxidant and can offer benefits to patients suffering from conditions such as atherosclerosis and cancer where there is extensive oxidative tissue damage. Human epidemiological studies have clearly demonstrated that diets that are rich in fruits and vegetables can significantly reduce predisposition to health conditions such as cancer and heart diseases but there is no conclusive evidence to attribute these benefits to vitamin C4.
In the last two decades the potential role of vitamin C as an anticarcinogenic agent has drawn lot of interest and has also been a subject of intense scientific debate. The interest in vitamin C as a potential anti-cancer agent began to take shape when studies indicated that certain properties of vitamin C make them highly antagonistic to cancer cell growth and proliferation. While some other studies did record some encouraging results initially, investigations involving controlled randomized trials that were carried out later could not prove any anti-cancerous properties of vitamin C scientifically.
In the seventies and the eighties Nobel Laureate Linus Pauling and a Scottish surgeon Ewan Cameron studied the therapeutic role of vitamin C against cancer and observed that those terminal cancer patients who were regularly given the compound would live at least 3 to 4 times longer than those who did not take vitamin C3. These claims were however refuted by a couple of studies carried out by researchers at the Mayo clinic. In the recent years, researchers from the Memorial Sloan-Kettering Cancer Center in New York states that vitamin C can significantly reduce the efficacy of chemotherapy and radiation in cancer patients but other researchers from the University of Colorado Health Sciences Center present the argument that vitamin C being an excellent antioxidant can not only protect the healthy cells from oxidative stress but can also arrest cancer cell growth and proliferation3.
Even though vitamin C is well-known for its antioxidant properties it can also act as a pro-oxidant agent depending on the dose5. A study carried out by Putchala et al. focused on the pro-oxidant reaction of vitamin C and evaluated if this could serve as a potential anti-cancer therapy. The results indicated that at concentrations of 0.5-2mM ex vivo in humans, vitamin C shown pro-oxidant cytotoxic effects against cancer cells. Another study carried out by Padayatty et al. demonstrated that vitamin C, when administered intravenously at a dosage of around 10-20 gm, its plasma concentration can go up to 14,000 μmol/L creating toxicity for carcinogenic cells6. Similarly, Chen et al. observed that Vitamin C, when administered intravenously at high concentrations produce free radicals such as hydrogen peroxide that is toxic to cancer cells.
Clinically, vitamin C can be administered intravenously as well as orally and when it was observed recently that the effect of the compound in the body is very different when given through vein, the interest on the compound as an anti-cancer agent increased once again2. These conflicting studies highlight the point that Vitamin C is effective for some patients but not others, indicating that one needs to personalize treatment options according to the effect the vitamin has.
Scientific studies have clearly shown that chemotherapy and vitamin C, when combined together can greatly reduce the size of the tumors compared to chemotherapy treatment alone1. Another study carried out in 2014 showed that ovarian cancer patients who received a combined treatment of chemotherapy and vitamin C administered intravenously had lesser chemotherapy related side-effects compared to those who only received chemotherapy1. Furthermore, Vitamin C has the property to synergistically improve the bioactivity of compounds such as β-glucans which is a primary constituent of mushroom extracts such as Maitake D-fraction. Maitake D-fraction has major immunomodulatory and antitumor properties and is also an ideal therapeutic agent against conditions such as diabetes and obesity8.
These are undoubtedly encouraging observations but there is still no concrete evidence to prove that vitamin C can actually cure malignancies. There are studies going on to see if vitamin C can augment the effect of chemotherapy and radiation against tumor cells but unless there is credible evidence on the table in the form of successful clinical trials, the debate on the role of vitamin C in cancer therapy will continue.
Casciari, J., Riordan, N. S. T. M. X., Jackson, J. & Riordan, H., 2001. Cytotoxicity of ascorbate, lipoic acid, and other antioxidants in hollow fibre in vitro tumours. Br. J. Cancer, Volume 84, pp. 1544-50.
Moynihan, T. (2014). High-dose vitamin C: Can it kill cancer cells? – Mayo Clinic. Mayoclinic.org. Retrieved 22 February 2016, from http://www.mayoclinic.org/diseases-conditions/cancer/expert-answers/alternative-cancer-treatment/faq-20057968
Gottlieb, N. (1999). Cancer Treatment And Vitamin C: The Debate Lingers. JNCI Journal Of The National Cancer Institute, 91(24), 2073-2075. http://dx.doi.org/10.1093/jnci/91.24.2073
National Cancer Institute,. (2015). High-Dose Vitamin C. Retrieved 23 February 2016, from http://www.cancer.gov/about-cancer/treatment/cam/patient/vitamin-c-pdq/#link/_9
Padayatty, S., Katz, A., Wang, Y., Eck, P., Kwon, O., & Lee, J. et al. (2003). Vitamin C as an Antioxidant: Evaluation of Its Role in Disease Prevention. Journal Of The American College Of Nutrition, 22(1), 18-35. http://dx.doi.org/10.1080/07315724.2003.10719272
Putchala, M., Ramani, P., Sherlin, H., Premkumar, P., & Natesan, A. (2013). Ascorbic acid and its pro-oxidant activity as a therapy for tumours of oral cavity – A systematic review. Archives Of Oral Biology, 58(6), 563-574. http://dx.doi.org/10.1016/j.archoralbio.2013.01.016
Padayatty, S. (2006). Intravenously administered vitamin C as cancer therapy: three cases. Canadian Medical Association Journal, 174(7), 937-942. http://dx.doi.org/10.1503/cmaj.050346
Chen, Q., Espey, M., Sun, A., Lee, J., Krishna, M., & Shacter, E. et al. (2007). Ascorbate in pharmacologic concentrations selectively generates ascorbate radical and hydrogen peroxide in extracellular fluid in vivo. Proceedings Of The National Academy Of Sciences, 104(21), 8749-8754. http://dx.doi.org/10.1073/pnas.0702854104
Konno, S. (2009). Synergistic potentiation of D-fraction with vitamin C as possible alternative approach for cancer therapy. International Journal Of General Medicine, 91. http://dx.doi.org/10.2147/ijgm.s5498