New Zealand researchers have established that vitamin C can help to block the growth of cancer cells - an important experimental finding they expect could be quickly adopted into cancer treatment.

The role of vitamin C in cancer treatment has been controversial for decades, with contradictory findings from various studies. In an international review of 20 human trials of vitamin C and other "anti-oxidant" supplements, the influential Cochrane Collaboration found no convincing evidence that they could prevent gastro-intestinal cancers - and said they "even seem to increase mortality".

But now a team from Otago University at Christchurch, in a paper published in leading international journal Cancer Research, have shown that vitamin C has a role in controlling tumour growth.

They say their study of tumorous and normal tissue samples from women with cancer of the uterine lining provides the first direct evidence of a link between vitamin C and a protein called HIF-1.

HIF (hypoxia inducible factor)-1 is considered a key protein in tumour survival. High activity of it promotes tumour growth and resistance to chemotherapy and radiotherapy and is linked with a poor prognosis for patients.

The Christchurch study, led by Associate Professor Margreet Vissers, of the university's Free Radical Research Group, found that high-grade tumours had around 40 per cent less vitamin C than matched, adjacent, normal tissue.

The researchers say their study suggests that restoring the vitamin C levels in tumours would limit factors that promote tumour growth, and recommend animal trials to test the hypothesis.

Professor Vissers said the study suggested it would be beneficial for people with cancer cells to have more vitamin C. It could help restrict the rate of tumour growth, increase responsiveness to chemotherapy and might prevent formation of solid tumours.

"There's enough information now for people to be seriously thinking about doing this, to apply this to the clinic or be setting up some clinical trials," she told the Herald yesterday.

"Anti-oxidant supplementation may not end up delivering any more vitamin C to the tumour.

"Just supplementing people may not actually have the effect that you want because you haven't done it in the right way," Professor Vissers said.

She said vitamin C levels in the body could be raised only to a certain level by oral supplementation.

Intravenous injections could achieve a higher level.

"That's the question: what's the best way to deliver vitamin C to the tumour."