Vitamin C (or L-ascorbic acid) has been reported as a pro-oxidant, with selective toxicity against certain types of tumour cells.
At the same time, a lower glutathione level has been said to be vital to reducing oxidative stress caused by xenobiotic toxins — substances foreign to the body — such as oxidants and metals linked to diseases like cancer, heart disease, and stroke.
Because of this, high intravenous doses of both vitamin C and glutathione have been used as complementary, alternative and adjuvant medication for treating cancer patients.
C-ing the benefits
Researchers at South Korea's Dongduk Women's University and YCH Hospital conducted a review of the molecular mechanisms behind the regulation of oxidation and reduction, with a focus on how pharmacological vitamin C could help alter the profile of the metabolites in cancer cells.
They also explored vitamin C's role in energy metabolism and its impact on cancer cell death.
They reported that several biological and pre-clinical studies imply that a high dose of intravenous vitamin C, in combination with conventional chemotherapy, "synergistically increase" the effectiveness of cancer treatment.
In addition, a phase I study found that high-dose intravenous vitamin C, when combined with the anti-cancer drugs erlotinib and gemcitabine, did not lead to heightened toxicity in patients with metatastic pancreatic cancer.
At the same time, the researchers wrote that vitamin C induced a high level of reactive oxygen species (ROS), as well as glutathione oxidation.
Treatment with vitamin C was also said to bring about changes in reduced glutathione ratio, which resulted in altered glutathione metabolism.
There have been many studies on the impact of different vitamins on cancer risk and cancer patients, as well the standard treatments they receive, namely radiotherapy and chemotherapy.
Lowered risk of colorectal cancer, cervical cancer and lung cancer has been linked to vitamin E alone. A Japanese study stated that higher vitamin D levels were associated with reduced overall cancer risk, but added that there was a 'ceiling effect' to these benefits.
A Hong Kong study conducted in 2016 questioned the safety of vitamin C supplementation for liver cancer patients, saying that despite antioxidants being able to slow the growth of cancer cells, a high level of antioxidants in the body would diminish this impact and eventually, even lead to cancer cell growth.
The researchers behind the current study concluded: "From the information available, it seems clear that vitamin C is involved in a variety of oxidative mechanisms. Therefore, vitamin C may be an adjuvant medicine combined with conventional chemotherapy drugs to induce cancer cell death.
"In the future, another issue pertaining to vitamin C is whether its use as an adjuvant medicine is valid in all populations or only in some populations, depending on the range of intakes. Therefore, further studies are required to identify the molecular targets of vitamin C sensitivity."
Source: Frontiers in Physiology
"Vitamin C in Cancer: A Metabolomics Perspective"
Authors: Seyeon Park, et al.