Behind the headlines: Does vitamin C stop cancer drugs working?

Vitamin C supplements may reduce the effectiveness of a wide range of anti-cancer drugs, media reports suggest.

The effect of vitamin C on cancer treatment has been debated for some time. Some studies have suggested that, as an anti-oxidant, vitamin C might protect normal cells and so be beneficial for cancer patients.

On the other hand, since some anti-cancer drugs produce reactive oxygen species, which kill cancer cells, if vitamin C reduced levels of these it would reduce the effectiveness of chemotherapy treatments.

A new study, published in the journal Cancer Research, found that vitamin C reduced the effectiveness of five different chemotherapy drugs both in vitro and against mice tumours.

What is the research?
Dr Mark Heaney and colleagues from the Memorial Sloan-Kettering Cancer Center, New York, looked at the effect of vitamin C pre-treatment of leukaemia and lymphoma cells, and tumours in mice, on the efficacy of five chemotherapy drugs: doxorubicin, cisplatin, vincristine, methotrexate and imatinib.

They found that for all five pre-treatment with vitamin C reduced their effectiveness against cancer cells and that the size of this effect increased with larger doses of vitamin C.

Further experiments suggested that vitamin C afforded protection to the cancer cells by limiting mitochondrial damage by reactive oxygen species.

What do the researchers say?
'The use of vitamin C supplements could have the potential to reduce the ability of patients to respond to therapy.

'Vitamin C appears to protect the mitochondria from extensive damage, thereby saving the cell. And whether directly or not, all anti-cancer drugs work to disrupt the mitochondria to push cell death,' Dr Heaney said.

What do other researchers say?
Dr Joanna Owens, Cancer Research UK's senior science information officer, said that the results were premature.

'As yet, there is not enough evidence to know whether antioxidants such as vitamin C are helpful or harmful during cancer treatment,' she said.

'It is possible that high doses of antioxidants can make treatment less effective, but until we know for sure our advice is to try to get the vitamins you need through a balanced diet rather than through supplements.'

Cancer Research 2008; 68: 8,031-8

Informing patients

- Evidence is unclear on whether vitamin C supplementation affects cancer treatment.

- Patients should obtain vitamins through an appropriate diet, rather than supplements.

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