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Vitamin C not proven to 'boost' chemo

Monday 10 February 2014

"Vitamin C keeps cancer at bay, US research suggests," was the inaccurate headline on the BBC News website. The study it reports on did not find that high-dose vitamin C helped with cancer survival, although it did appear to show it reduced some chemotherapy-related side effects.

The study actually looked at whether vitamin C could improve the effectiveness of chemotherapy – specifically for women with late-stage ovarian cancer.

The vitamin C doses were given intravenously (not as tablets or food) in both mice and humans. The part of the trial conducted on people was too small to prove whether vitamin C helped kill cancer cells or increased survival from cancer up to five years after diagnosis. The results were not statistically significant, and any beneficial effects could have been down to chance alone.

However, the research did suggest that vitamin C may reduce chemotherapy side effects for women, but again it was too small to prove it with any confidence. It's also worth noting that the women knew whether they were given vitamin C, so the placebo effect may have influenced their reporting of side effects.

Potential treatments that reduce the unpleasant side effects of chemotherapy (or improve its effectiveness) are worth investigating. But vitamin C's effect on cancer survival, or on reducing side effects, is not yet proven.

A large human clinical trial investigating the intravenous effects of vitamin C, combined with standard chemotherapy, in a range of cancers would answer many of the outstanding questions this preliminary study has raised, and address its limitations.

Where did the story come from?

The study was carried out by researchers from the University of Kansas in the US, and was funded by the Gateway for Cancer Research Foundation, the University of Kansas Endowment, the University of Kansas Medical Center Research Institute and the US National Institutes of Health.

It was published in the peer-reviewed journal, Science Translational Medicine.

The quality of the BBC's reporting on the study was mixed. On the plus side, the BBC included accurate and appropriately balanced quotes from a cancer expert, saying: "It's difficult to tell with such a small trial – just 22 patients – whether high-dose vitamin C injections had any effect on survival, but it's interesting that it seemed to reduce the side effects of chemotherapy."

The expert went on to say that, "Any potential treatment for cancer needs to be thoroughly evaluated in large clinical trials to make sure it's safe and effective, so further studies are needed before we know for sure what benefits high-dose vitamin C may have for patients."

On the negative side, its original headline (which has now been changed) – "Vitamin C keeps cancer at bay" – was a misleading summary of the study's findings. There is no credible evidence that vitamin C can prevent cancer.

However, this reporting may in part be down to the rather overenthusiastic press release from the University of Kansas Medical Center, which claimed that, "Researchers establish benefits of high-dose vitamin C for ovarian cancer patients".

The researchers' claim that, "Pharmaceutical companies are unlikely to run trials, as vitamins cannot be patented" has also been accepted uncritically. Such a blanket statement is certainly up for debate – studies involving vitamins have already been funded by pharmaceutical companies. There are many other ways to fund research into existing treatments, including through government, academic and charitable funding.

Read more about clinical trials and medical research.

What kind of research was this?

This research was a mix of laboratory-based cell studies, studies using mice, and studies using humans investigating the potential anti-cancer properties of vitamin C on cancer of the ovaries (ovarian cancer).

The study authors said vitamin C has been suggested as a cancer treatment for decades, most famously by Nobel Prize-winning chemist, Linus Pauling. However, early research involving giving people vitamin C orally (through the mouth) showed no beneficial effects, so this avenue of research was largely abandoned.

Since then, there has been increasing anecdotal evidence that vitamin C may still be useful as an anticancer medicine if used in high concentrations and given directly into the vein (intravenously), rather than orally.

This research aimed to investigate the effects of using high doses of intravenous vitamin C on ovarian cancer to shed light on the issue.

What did the research involve?

The researchers first investigated the effect of vitamin C on human ovarian cancer cells at a cellular and molecular level in the laboratory. They tested vitamin C alone, but also in combination with carboplatin, the main chemotherapy drug used to treat ovarian cancer, to see if there were any combined (synergistic) effects.

Encouraged by the results, the researchers transferred human ovarian cancer cells into mice to see if the cancer cells would be affected by the combined chemotherapy and vitamin C treatment in a living organism.

The results again proved encouraging, culminating in a small clinical trial involving 27 volunteers with newly diagnosed later stage (stage III and IV) ovarian cancer – that is, cancer that has spread outside the pelvis.

The participants in the human trial were randomised to receive one of the following treatments intravenously for six to 12 months, and were followed up for five years to see how long they survived:

  • paclitaxel/carboplatin therapy (the standard chemotherapy treatment for people with ovarian cancer)
  • paclitaxel/carboplatin therapy plus high-dose vitamin C (standard chemotherapy plus vitamin C)

Standard chemotherapy was given for six months, with the additional vitamin C element given for 12 months.

During the trial, the researchers measured many different aspects of toxicity and side effects caused by the chemotherapy treatment.

Two of the 27 participants withdrew because they wanted chemotherapy and vitamin C, but weren't in this group, so the main analysis involved 25 people.

What were the basic results?

The most relevant and advanced results were those from the small human clinical trial. The main results from this were:

  • Survival from cancer over the five-year period looked slightly better with vitamin C in addition to standard chemotherapy, but the survival difference was not statistically significant. This means there was either no effect on survival, or the study was too small to detect an effect.
  • Side effects classed as mild to moderate (grade 1 or 2 toxicity) associated with the chemotherapy treatment were significantly lower in the group receiving chemotherapy and vitamin C compared with those receiving chemotherapy alone. The small number of severe or life-threatening side effects experienced (grade 3 or 4) was not significantly different between the two treatments.

How did the researchers interpret the results?

The researchers' main interpretation was that, "On the basis of its potential benefit and minimal toxicity, examination of intravenous ascorbate [vitamin C] in combination with standard chemotherapy is justified in larger clinical trials."


Among 25 newly diagnosed ovarian cancer patients, those given vitamin C alongside standard chemotherapy were found to have significantly fewer mild to moderate treatment-related side effects than those on standard treatment.

However, the researchers found no significant differences in terms of cancer survival, which was assessed up to five years after treatment. One explanation for this is that the study was too small to detect any effect, but this could also be because no survival benefit actually exists.

It's also worth noting that the women knew whether they were given vitamin C, so the placebo effect may have influenced reporting of side effects. This is particularly relevant, as two participants actually withdrew from the study because they were allocated standard chemotherapy but wanted to receive vitamin C as well. This gives an indication that at least some of the participants were expecting greater benefits through receiving vitamin C.

Consequently, while there are tentative signs that high-dose intravenous vitamin C may have the potential to complement existing chemotherapy treatments in treating ovarian cancer, this has not yet been proven convincingly.

The conclusions that we are able to draw from this research are limited by its small sample size (just 25 people) and its sole focus on ovarian cancer, rather than a range of cancers. These points limit the reliability and generalizability of its results for all cancers at this stage.

A large human clinical trial investigating the intravenous effects of vitamin C, in combination with standard chemotherapy, in a range of cancers would provide the reliability that the current study lacks.

Analysis by Bazian
Edited by NHS Website

Links to the headlines

Vitamin C can help 'keep cancer at bay'

The Independent, 9 February 2014

Links to the science

Ma Y, Chapman J, Levine M, et al.

High-Dose Parenteral Ascorbate Enhanced Chemosensitivity of Ovarian Cancer and Reduced Toxicity of Chemotherapy

Science Translational Medicine. Published online February 5 2014