Vitamin C is synthesized from glucose by most of the animals in the kidney of the liver. But in humans and other primates like the guinea pig, it lacks this mechanism due to some mutation inactivating the gene coding for L-gluconolactone oxidase (GULO). It is an enzyme involved in the catalytic step of vitamin C synthesis. Our immune cells have a 10 to 100 times higher concentration of Vitamin C than the blood and any other cell. Vitamin c is required at every step of the process, from detecting cancer cells to killing the cancer cells. The daily recommendation of vitamin C is 75–90mg per day.
Vitamin C therapy is considered a great approach to cancer treatment. This approach improved the quality of life for cancer patients. Several studies have demonstrated that a millimolar concentration of vitamin c can kill cancer cells in vitro and slow down tumour growth in vivo. In contrast, the normal cells of the body remain resistant to it. However, the mechanism of action of vitamin C towards the cancer cells is poorly understood. The mechanism basis could depend on the type of cancer, therapy combined with vitamin C therapy, and many others. A study shows that Patients with cancer often have lower plasma concentrations of ascorbate than healthy adults, and vitamin C deficiency is associated with increased cancer mortality. A meta-analysis of 21 studies, including 9,000 lung cancer cases where male adults who took 100mg vitamin C per day had a 7% reduced risk of lung cancer, showed a relation between vitamin C intake and cancer risk among individuals. This dose is also associated with breast-cancer-specific mortality in women.
MECHANISM OF ACTION
In vitro cytotoxic effect of ascorbic acid on various cancer cells is mediated through a chemical reaction that generates hydrogen peroxide. Hydrogen peroxide plays an important role within the selective toxicity of ascorbate and induction of oxidative DNA damage/cancer necrobiosis. An in vitro study found that ascorbic acid killed colorectal cancer cells with mutations by inhibiting the enzyme glyceraldehyde 3- phosphate dehydrogenase. Several kinds of research suggested that pharmacological doses of ascorbic acid enhance the effects of Arsenic trioxide on ovarian cancer cells and Gemcitabine on pancreatic cancer cells. Combining vitamin C with chemotherapy has shown improved outcomes. Combining vitamin C with chemotherapy has shown improved outcomes.
Intravenous vs oral vitamin c
Vitamin c therapy can be administrated by two routes – oral and intravenous ascorbate. In the initial trials, the ascorbate was administrated intravenously and achieved a peak plasma concentration of 6mm, but when ascorbate was administrated orally, it achieved less than 200μM plasma concentration. Therefore, it is widely accepted that the millimolar concentration of ascorbate needed to induce cytotoxicity in cancer cells can be achieved only when administered intravenously. Phase I dose-finding studies in cancer patients recommend using 1.5 g to 2 g intravenous vitamin C per kg body weight three to four times per week. It is advised to start out treatment with a lower dose and, if no adverse events are observed, to gradually increase doses to their final level. In a study of patients diagnosed with stage III/IV ovarian cancer when they received conventional therapy combined with intravenous vitamin C, it was found that high-dose vitamin C reduces toxicities associated with chemotherapy. Vitamin C infusions were either used as a sole treatment or combined with conventional therapy.
Vitamin C therapy – Safe or not
Vitamin C itself is non-toxic. Some contradictions are still there regarding vitamin c therapy. In general, high-dose intravenous vitamin C results in mild and consistent side effects. Glucose 6-phosphate dehydrogenase deficiency in patients was found to be at higher risk to experience hemolysis ( breakdown of red blood cells) by administration of high doses of vitamin c; therefore, there is a need to screen the patient for this metabolic deficiency before undergoing vitamin c therapy. The end product of metabolic oxidation of vitamin C is oxalic acid, subjected to the risk of oxalate crystallization in the kidney of a patient with renal dysfunction. Haemorrhage (bleeding) is also one of the concerns of this therapy; therefore, a gradual increase of intravenous vitamin C is advised along with monitoring the patient. Several studies show that there was also an association between breast cancer occurrence and total vitamin C intake.
The study suggested an association between vitamin C intake and the occurrence of hormone receptor status-specific types of breast cancer. Recent literature reveals the influence of vitamin C on prostate cancer. Still, it concludes that dietary intake of vitamin C and healthy diet elements are promising in the prevention and therapy of prostate cancer.
People can get a good amount of vitamin C from their diets. All fruits and vegetables
have some source of vitamin C. Some of the best sources are:
- Green peppers
- Citrus fruits and juices
- Sweet potatoes