Can vitamin C treat cancer?
This may very well be one of the most debatable topics in oncology. High dose vitamin C has been studied as a cancer treatment since 1970’s but not without its share of controversies. But a new study from the University of Iowa (UI) published in Redox Biology shed some light into why the efficacy of high dose vitamin C as cancer therapy has shown mixed results.
Most vitamin C therapies to treat cancer involves oral administration. However, massive amounts of vitamin C taken in this form is degraded during digestion and is usually excreted by the body. On the other hand, intravenous administration achieves a much higher concentration of vitamin C in the blood (almost 500 times higher than what you would typically realize through oral use) as it bypasses the normal digestion and excretion process.
It is the high levels of vitamin C in your blood that plays a critical role in fighting and destroying the cancer cells; probably the reason why oral intake of vitamin C doesn’t always assure promising results. It is important to note that using liposomal vitamin C also achieves very high levels of vitamin C in the bloodstream and in fact this approach is much more convenient and cost effective than using intravenous vitamin C infusions.
In this recent study, the UI scientists proposed a mechanism how high levels of vitamin C selectively kills cancer cells while leaving healthy, normal cells undamaged – indicating that it might not be the antioxidant properties that help vitamin C fight cancer. 
High dose vitamin C shows selective toxicity to cancer cells
The scientists found that in the body vitamin C rapidly degenerates into hydrogen peroxide (H2O2), a free radical. Now, this may sound contradictory as free radicals cause oxidation, damaging DNA and other cellular structures; and the body uses antioxidants such as vitamin C to target and destroy these free radicals. So, how does this therapy work?
- Healthy cells use several mechanisms to efficiently remove H2O2 – limiting toxic build-up of free radicals and the resulting oxidative damage. One of the primary routes to neutralize H2O2 is the enzyme catalase. Catalase is present in abundance in healthy cells and tissues.
- Most human cancer cells produce scant amounts of catalase – suggesting the majority of cancer cells don’t have the necessary bio-chemical tools to neutralize high concentrations of H2O2.
- When these tumour cells are flooded with high amounts of vitamin C, it results in excessive generation and accumulation of hydrogen peroxide free radical in the cancerous tissue. The limited capacity to detoxify H2O2 proves lethal to malignant tumour cells.
Gary Buettner, the lead researcher, who is also a professor of radiation oncology and a member of Holden Comprehensive Cancer Center at the University of Iowa, explains that cancer cells are not as efficient in detoxifying hydrogen peroxide as normal cells – making tumour cells more susceptible to the damage and death by the free radical. “This explains how the very, very high levels of vitamin C used in our clinical trials do not affect normal tissue, but can be damaging to tumour tissue,” adds Buettner. 
Lower catalase levels equals increased damage to cancer cells
The researchers also discovered that cells with lower catalase activity were more likely to be damaged on exposure to vitamin C. “Our results suggest that cancers with low levels of catalase are likely to be the most responsive to high-dose vitamin C therapy, whereas cancers with relatively high levels of catalase may be the least responsive,” Buettner explains. This is an important insight to help determine the types of cancers that can be effectively treated with high-dose vitamin C therapy.
Vitamin C as an effective adjunct in cancer treatment
The UI scientists are now conducting clinical trials for pancreatic and lung cancer that use high dose intravenous vitamin C in conjunction with conventional cancer treatment (chemotherapy or radiation). The preliminary trials indicate that the treatment appears to improve the outcome in cancer patients. Most importantly, it is safe, well-tolerated and with no significant side effects unlike standard cancer treatments that cause collateral damage – weakening the immune system and targeting both healthy and cancer cells alike.
With these promising initial results, large-scale trials are underway that aim to determine whether the therapy would have any positive effect on patient survival.
- Garry R. Buettner et al. Tumor cells have decreased ability to metabolize H2O2: Implications for pharmacological ascorbate in cancer therapy. Redox Biol. 2016.
- Jennifer Brown. Why high-dose vitamin C kills cancer cells. The University of Iowa. 2017.