It made big headlines last week – hailed as a ‘breakthrough’, could humble vitamin C be a new cancer treatment? Let’s peel back the story and find out whether it’s worth the hype.

Vitamin C and cancer – a brief history

Using vitamin C to treat cancer isn’t a new idea. Back in the 1970s, double Nobel-prize winning scientist Professor Linus Pauling was convinced of its cancer-fighting potential. The initial trials, which he carried out with Scottish doctor Ewan Cameron, showed that giving high doses of the vitamin to terminal cancer patients provided survival benefits (the papers are here and here ). But these experiments attracted some criticism as they hadn’t included patients given a ‘dummy drug’ or placebo.

Two later randomised placebo-controlled trials carried out in the USA found little benefit from taking vitamin C tablets as a cancer treatment. The results (published here and here) persuaded the scientific community to take the vitamin off their radar.

New results

But an interesting new study published in the journal PNAS brings vitamin C back into the limelight.

A team of US researchers, led by Mark Levine, have shown dramatic results from injecting high doses of vitamin C into mice implanted with brain, ovarian and pancreatic tumours. These are all particularly aggressive forms of the disease that are difficult to treat. The team found a reduction in tumour weight of between 41 and 53 per cent. And in mice with glioblastoma (brain) tumours, the treatment also prevented the cancer from spreading to other organs. In contrast, around one-third of the untreated animals showed signs of the cancer spreading.

But if these experiments are so encouraging, why did the earlier randomised clinical trials of vitamin C show little benefit? The problem could be in the way the vitamin was given to patients.

In the randomised clinical trials that led to the dismissal of vitamin C, patients were given it in tablet form. But evidence emerging over recent years indicates that the body tightly controls the amount of vitamin C absorbed from the gut, limiting the amount that reaches the blood and tissues.

So a key finding in the new study suggests that to get the high levels needed to show cancer-fighting effects, we need to inject high doses of vitamin C – giving a tangible explanation as to why those tablet trials didn’t show survival benefits. This finding also suggests that taking vitamin C supplements won’t help people with cancer.

But how does it work?

So how does vitamin C actually work as a cancer treatment? Levine thinks that the high doses of the vitamin react with the unique chemistry of tumour cells, producing hydrogen peroxide – and it’s this chemical that kills the cancer cells.

To test this, the researchers added an enzyme called catalase – an enzyme that breaks down hydrogen peroxide, along with vitamin C, to cancer cells grown in the lab. This neutralised the anti-cancer effects of the vitamin C, suggesting their theory is correct.

Back in the limelight?

It looks like we may have gone full circle with vitamin C as a potential cancer treatment. The new evidence is certainly encouraging and warrants further investigations. But, as is often the case, we can’t get too excited just yet.

Until we carry out randomised controlled clinical trials with patients we simply don’t know whether injecting high doses of vitamin C will be an effective way to treat cancer. And it’s also possible that it could interact with standard cancer treatments such as radiotherapy and chemotherapy, limiting their effectiveness . This may not be the case, but at the moment we’re being cautious. There is so little research on this subject that we just don’t know yet how vitamin C might affect cancer patients.

Alison Ross is a science information officer.

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