New research on folic acid has largely dismissed the cancer concerns that led to the Government's going cold on plans for its mandatory addition to bread.

Food Safety Minister Kate Wilkinson in August deferred the plan until 2012 but the new research has prompted a call for a rethink.

Her move was based on public submissions, sought after a campaign by the food industry against "mass medication" and which highlighted evidence linking the vitamin to increased cancer risk.

But now the Food Standards Agency in Britain, where similar concerns were raised, has released research that concludes: "The new evidence does not provide a substantial basis to change [the] previous recommendation for the introduction of mandatory fortification" of bread flour.

Folic acid is the synthetic form of folate, a B vitamin present in many foods including leafy vegetables and wholemeal bread.

As the New Zealand diet contains too little, women are encouraged to take folic acid supplements when planning to become pregnant, to reduce the risk of fetuses with defects like spina bifida. Fortification was proposed because many pregnancies are not planned, although supplementation would still have been advised.

Some foods are voluntarily fortified. Mandatory addition to most bread was to start in September, until the Government opted out of a transtasman regulation under which Australia has introduced mandatory addition of folic acid to bread flour.

Britain's Scientific Advisory Committee on Nutrition, which was asked to assess the new evidence on folic acid, found:

* It may be linked with increased risk of colorectal cancer in people with, or who have had, precancerous bowel growths, or older people at risk of developing them.

* Increased colorectal cancer incidence had coincided with the start of fortification in the United States and Canada, but "no clear explanation" was found. The data were insufficient to confirm the suggestion it was because of improved cancer screening.

* Studies involving 35,600 people showed folic acid did not have a statistically significant effect on cancer incidence, but the possibility of a link could not be excluded. The statistical power of such studies to detect an effect of the vitamin on cancer risk was unavoidably limited.

* The reported link to an increased risk of prostate cancer may be spurious because this study was based on a small number of prostate cancer cases.

"... the committee agreed that there were still uncertainties regarding folic acid and cancer risk; [its] original recommendation had taken this into account by trying to limit exposure to high intakes."

Ms Wilkinson said yesterday that one reason for the New Zealand deferral was to allow new research to be considered.

But the Government would not revisit mandatory folic acid fortification until it reviewed the transtasman rule on it in 2012.

John Forman, of the Organisation for Rare Disorders, which supports mandatory fortification, said the British findings were "exactly what we expected" and should prompt the Government to start the review now.