Little clinical evidence supports the use of high-dose intravenous vitamin C to treat cancer

Key takeaway

Although some studies performed in laboratory-grown cells and mice found that vitamin C can selectively kill cancer cells, there’s no evidence showing the same effect in people. Clinical trials didn’t find any benefits in patients who took vitamin C orally, but the oral route of administration leads to much less vitamin C in the blood compared to the intravenous route. The higher doses that can be reached through intravenous vitamin C have yet to be tested in large-scale clinical trials in cancer patients.

Reviewed content

Verdict:

Unsupported

Claim:

Intravenous vitamin C specifically kills only cancer cells and not healthy cells

Verdict detail

Inadequate support: Although several preclinical studies performed in cell cultures and in mice found evidence that vitamin C can selectively kill cancer cells, there’s no clinical evidence showing that the same effect occurs in people.

See our method of evaluation

Full Claim

“Instead of treating cancer with chemotherapy, you can give intravenous vitamin C; 30, 60, a hundred, a thousand milligrams a day, directly into the bloodstream, and that will kill cancer cells. Vitamin C at that high dose is selectively toxic to cancer cells, and that’s exactly what chemotherapy is. But with vitamin C there is no damage to healthy cells”

Vitamin C, also known as ascorbic acid, is a nutrient with antioxidant properties that plays a key role in important bodily functions, including the production of collagen. Vitamin C deficiency causes various alterations and can lead to scurvy, an ailment characterized by anemia, internal bleeding, and tooth decay.

In September 2022, several posts on social media platforms went viral, claiming that intravenous administration (entering the body through a vein) of vitamin C is an effective treatment for cancer, without the negative effects associated with chemotherapy, such as fatigue or hair loss (like this TikTok video and this Facebook video). As we will explain in this review, scientific evidence to support the use of vitamin C as a cancer treatment is lacking. 

The use of vitamin C for cancer treatment was first proposed in the 1950s by physician William J. McCormick, who hypothesized that cancer metastasis was caused by poor collagen formation due to vitamin C deficiency, based on observations in cancer patients^[1].

The alleged therapeutic benefits of vitamin C were widely promoted during the 1970s by Linus Pauling, a chemist who had won the Nobel Prizes in Chemistry (1954) and Peace (1962). Notably, Pauling proposed that high-dose supplementation of vitamin C reduced the incidence of common colds, a hypothesis that isn’t supported by scientific evidence^[2].

The therapeutic effect of vitamin C for cancer treatment was first tested in the 1970s in two studies conducted by Pauling and Ewan Cameron, a physician who hypothesized that vitamin C could suppress cancer development by inhibiting the action of an enzyme called hyaluronidase. In these studies, 100 patients with various types of terminal cancer were given vitamin C both orally and by injection^[3,4]. The disease progression of each participant was retrospectively compared with ten patients treated identically, who hadn’t been given vitamin C. 

Both studies reported improved quality of life and survival time in patients receiving vitamin C. However, the design of both studies contained numerous flaws, as explained in this article for Science-Based Medicine by oncologist David Gorski:

“The study’s flaws, which were too numerous to mention, rendered its results essentially meaningless. If you want a quote from his original paper that shows this better than anything, here it is: ‘We believe that the ascorbate[vitamin C]-treated patients represent a random selection of all the terminal patients in the hospital, even though no formal randomization process was used.’ Suffice it to say that, in a clinical trial, it is not sufficient to ‘believe’ that your groups were properly randomized and matched. You have to show it.

[…] Undeterred, they published a follow-up study in 1978 that purported to confirm the findings of their 1976 study. It was little better. Pauling and Cameron used many of the same patients and selected a different control group, but the patients were still not matched for stage of cancer, age, or performance or nutritional status. It, too, was a shockingly poorly-designed study, even for a retrospective study.”

Two subsequent randomized controlled clinical trials conducted at the Mayo Clinic, published in 1979 and 1985, didn’t find that high-dose, orally-administered vitamin C improved cancer patients’ symptoms or survival time^[5,6].

One factor that could explain the vastly different results obtained in these studies is that the blood concentration of vitamin C differs greatly depending on whether it is administered orally or by injection, as explained in this article from the charity Cancer Research U.K. A study performed in 17 healthy volunteers found that intravenous administration of vitamin C resulted in blood concentrations as much as 70-fold higher than those achieved by oral administration^[7].

Some studies performed in laboratory-grown cells and mice suggest that the ability of vitamin C to kill cancer cells is linked to the production of hydrogen peroxide^[8] and other reactive oxygen species within the cell, which induces cell death. Such an effect was reported in human pancreatic tumor^[9] and human breast cancer cell lines^[10], among others.

According to a review published in 2020, some studies performed in cell cultures and in mice found that vitamin C can selectively kill cancer cells, however these results haven’t been replicated so far in large-scale clinical trials^[1]. Only a few clinical studies suggested that vitamin C could produce an anticancer effect from vitamin C. Other studies reported that vitamin C may help alleviate some of the side effects of chemotherapy like nausea and fatigue^[11,12], but this isn’t the same as having an anticancer effect.

It’s also important to keep in mind that such studies combined vitamin C with conventional cancer treatments like chemotherapy; they didn’t utilize vitamin C alone. There are other important caveats as well. Many of the clinical trials included in the review involved small numbers of patients and different types of cancer, which doesn’t allow us to generalize the observations from these trials to all cancer patients.

Similarly, a review published in 2021 concluded that “a large body of evidence is accumulating suggesting that [vitamin C], when administered intravenously and in high doses, has potent cancer-selective cytotoxic, cancer-therapy sensitizing and toxicity-reducing properties”, but also noted that clinical data, especially phase III clinical studies, is lacking^[13].

In conclusion, there’s no reliable clinical evidence showing that vitamin C cures cancer in people, contrary to a claim shared by social media posts. While scientists continue to investigate potential uses of intravenous vitamin C in cancer patients, the U.S. FDA hasn’t approved the use of intravenous vitamin C as a treatment for cancer, as there is no clinical evidence so far that it works. 

REFERENCES

• 1 – Roa et al. (2020) Therapeutic Use of Vitamin C in Cancer: Physiological Considerations. Frontiers in Pharmacology.
• 2 – Hemilä et al. (2013) Vitamin C for preventing and treating the common cold. Cochrane Database of Systematic Reviews.
• 3 – Cameron et al. (1975) The orthomolecular treatment of cancer: III. Reticulum cell sarcoma: Double complete regression induced by high-dose ascorbic acid therapy. Chemico-Biological Interactions.
• 4 – Cameron and Pauling (1976) Supplemental ascorbate in the supportive treatment of cancer: Prolongation of survival times in terminal human cancer. Proceedings of the National Academy of Sciences.
• 5 – Creagan et al. (1979) Failure of High-Dose Vitamin C (Ascorbic Acid) Therapy to Benefit Patients with Advanced Cancer — A Controlled Trial. The New England Journal of Medicine.
• 6 – Moertel et al. (1985) High-Dose Vitamin C versus Placebo in the Treatment of Patients with Advanced Cancer Who Have Had No Prior Chemotherapy — A Randomized Double-Blind Comparison. The New England Journal of Medicine.
• 7 – Padayatty et al. (2004) Vitamin C Pharmacokinetics: Implications for Oral and Intravenous Use. Annals of Internal Medicine.
• 8 – Chen et al. (2007) Ascorbate in pharmacologic concentrations selectively generates ascorbate radical and hydrogen peroxide in extracellular fluid in vivo. Proceedings of the National Academy of Sciences.
• 9 – Du et al. (2010) MECHANISMS OF ASCORBATE-INDUCED CYTOTOXICITY IN PANCREATIC CANCER. Clinical Cancer Research.
• 10 – Wong et al. (2013) SVCT-2 in breast cancer acts as an indicator for L-ascorbate treatment. Oncogene.
• 11 – Carr et al. (2014) The Effect of Intravenous Vitamin C on Cancer- and Chemotherapy-Related Fatigue and Quality of Life. Frontiers in Oncology.
• 12 – Ma et al. (2014) High-dose parenteral ascorbate enhanced chemosensitivity of ovarian cancer and reduced toxicity of chemotherapy. Science Translational Medicine.
• 13 – Böttger et al. (2021) High-dose intravenous vitamin C, a promising multi-targeting agent in the treatment of cancer. Journal of Experimental & Clinical Cancer Research.