Vitamin C and cancer risk and treatment

Vitamin C (L-ascorbic acid) works as a strong reductant, radical scavenger, and protector of cell membranes against primary peroxidative damage in tissues and in the extracellular fluid. L-ascorbic acid is involved in the synthesis of collagen and many other biologically relevant substances, enzyme activity, xenobiotic detoxification, and prevention of forming carcinogenic nitrosamines. It also plays a role in the immune system. Numerous data indicate that cancer patients suffer from vitamin C deficiency. Studies show that people with a low vitamin C intake have an increased risk of head and neck cancers as well as lung, gastric, pancreatic, cervical, rectal, or breast cancer. On the other hand, there is no clinical evidence to support the thesis that antioxidant supplements (including vitamin C) prevent cancer. Observational trials investigating high doses of intravenous L-ascorbic acid in previously treated cancer patients have shown that it allows an increase in quality of life and may improve physical, mental, and emotional functions, as well as reducing adverse effects of standard anticancer treatment, including fatigue, nausea, vomiting, and appetite loss. So far, there were a few randomized controlled trials and they have not reported any statistically significant improvements in the overall or progression-free survival with vitamin C, as compared to the control arm. However, preclinical data indicating a role of L-ascorbic acid in modulation of immune response and its involvement in epigenome remodeling suggest its new potential clinical applications in cancer patients, especially in combination with immunotherapy. It seems reasonable to further investigate the value of vitamin C as a supportive treatment or in combination with anticancer targeted therapy.