7 FAQs About Vitamin C for Cancer Treatment

High-dose vitamin C is a type of targeted therapy that eradicates cancerous cells.

Also referred to as megadose, it is administered intravenously in doses ranging from 25 to 75 grams. Although the treatment can be adminstered orally as well, intravenous administration is regarded as more effective.

The first clinical study on the effects of high-dose vitamin C was done in the 1970s by chemists Linus Pauling and Dr. Ewan Cameron. They claimed that intravenous injection of high-dose vitamin C greatly prolonged the survival of patients with advanced-stage cancer. Later, however, the National Cancer Institute found out that this study was inaccurate.

During a randomized, controlled study one group was given high-dose vitamin C orally and the other was given a placebo. At the end of the trial, no significant differences in survival or quality of life were found between the groups. 

In a randomized study on stages III to IV ovarian cancer, one group was treated with chemotherapy and  the other with both chemotherapy and high-dose vitamin C. The results showed no difference in survival or disease progression. The group with stages I to II cancer showed reduced adverse effects of chemotherapy following high-dose vitamin C administration. However, the group with grades III to IV cancer showed no such effects.

Recently, it has been reported that vitamin C administered intravenously has better effects on cancer treatment. However, it is still unclear whether high-dose vitamin C has anticancer properties and, if so, what types of cancer it can affect.

High-dose vitamin C produces hydrogen peroxide, a free radical that is toxic to cancer cells. Cancer cells lack catalase, an enzyme that decomposes hydrogen peroxide. Therefore, vitamin C treatment may help eliminate cancer cells while avoiding damage to healthy cells that possess the catalase enzyme.

High-dose vitamin C also strengthens the immune system by boosting the production of lymphocytes, which are white blood cells responsible for fighting disease.By increasing the activity of white blood cells in the body, the treatment can help prevents cancer from spreading to other areas of the body.

Although there is no proof that vitamin C alone can cure cancer, researchers are investigating whether it can improve the efficacy of other cancer therapies (such as chemotherapy and radiation therapy) or reduce the side effects of treatment.

Although extensive controlled clinical studies to support vitamin C's efficacy against cancer have not yet been conducted, preliminary research suggests that combining traditional therapies with high-dose vitamin C may be beneficial.

Several animal studies have reported that therapeutic doses of vitamin C may selectively kill cancer cells in vitro and slow the development of various human tumor xenografts in immunocompromised mice. However, there is still uncertainty about vitamin C's potential therapeutic function in cancer because the administration of large doses in patients with cancer has not demonstrated significant anticancer action.

High doses of vitamin C are believed to be safe since it is a water-soluble vitamin that is not stored in the body. However, there are several adverse effects and medication interactions associated with it:

• May exacerbate hemolytic anemia in people with glucose-6-phosphate dehydrogenase deficiency and the risk of renal failure in those with renal diseases.
• Not recommended for patients with hemochromatosis as vitamin C may improve iron absorption
• Reduces the absorption of vitamin B12 and copper
• May increase the risk of the development of kidney stones owing to its acidic nature; oxalic acid produced due to the metabolism of vitamin C can cause hyperoxaluria (excess oxalates in urine)
• May cause diarrhea due to its laxative effect
• May increase the risk of toxicity when large doses of vitamin C are given in conjunction with some chemotherapy treatments
• May cause serious side effects and increases the risk of:
  • Acute myeloid leukemia
  • Resistant metastatic colon cancer
  • Metastatic melanoma

High-dose vitamin C may reduce the effectiveness of certain cancer drugs, although these effects have so far only been shown in laboratory and animal research.

Vitamin C may even cause interactions with other drugs, such as:

• Bortezomib: Ascorbic acid significantly reduces the activity of bortezomib if both are taken at the same time. However, if bortezomib is administered in the morning and ascorbic acid in the evening, there is less interaction between the two drugs.
• Glutathione: As an antioxidant, glutathione lowers the prooxidant cytotoxic effects of vitamin C.
• Beta-blockers: In patients who have undergone bypass surgery, vitamin C can boost the cardioprotective benefits of beta-blockers.
• Acetaminophen: Vitamin C can enhance the degree of absorption of acetaminophen in healthy people and may increase the risk of adverse effects.

The FDA has not approved the use of high-dose vitamin C as a treatment for cancer. Moreover, the FDA does not consider dietary supplements as safe or effective.

However, many clinicians do advocate high-dose vitamin C as an alternative to cancer treatment because of its positive results against the symptoms and possible anticancer properties.