There is no evidence of an increased cancer risk from plans for bakers in New Zealand and Australia bakers to fortify their bread with folic acid, a leading scientist says.
A big "state of the art" scientific study which has not yet been published, "shows that there is no increase in cancer risk with high-dose folic acid", said Professor Murray Skeaff, a specialist in human nutrition at Otago University.
Prime Minister John Key has said the fortification of breads with folic acid is likely to go ahead in September but may be stopped soon after.
The folic acid fortification was ordered last year to prevent some devastating neural tube defects in babies, such as spina bifida, giving protection to women unaware they might be pregnant.
Bakers have criticised the move, complaining that it adds unreasonable costs, and Food Safety Minister Kate Wilkinson has called for a review - but not until October, a month after bakers have started adding it to bread.
Critics of the "mass medication" have claimed that though added folic acid will reduce birth defects - and may prevent premature birth and heart defects - extra-high levels may also pose a cancer risk to old people.
Animal studies show too much folic acid supplements in pills can spur some cancers.
And one study which tracked 640 men found that 10 years later, folic acid users were more likely to have developed prostate cancer.
Prof Skeaff said that on the basis of the cancer risk, "there is no reason the proposed fortification should not go ahead"
"There is no evidence of cancer risk."
At a conference in Prague two weeks ago, a pooled analysis of all the randomised control trials of folic acid were revealed by the clinical trials service unit at Oxford in Britain.
The results from around 35,000 individuals who participated in studies of high dosage folic acid supplementation in countries around the world "showed that there was no significant increase or decrease in the risk of cancer" Prof Skeaff said.
The trials used high dosage folic acid, ranging from 800 micrograms to about 2500 micrograms a day, compared with the proposed addition of 140 micrograms a day to the New Zealand diet.
The studies, mainly done in Europe and North America since the mid-1990s, found that folic acid and B vitamins had no effect on cancer risk in the people taking them.
"The results showed no evidence of increased risk for prostate cancer, and they showed no evidence of increased risk for colorectal cancer, which are the two forms of cancer for which some much smaller studies had previously found some evidence of increased risk," said Prof Skeaff.
"We can be confident on the basis of these trials that there is no evidence of cancer risk."
Lyall Thurston, speaking for a coalition of parents of children with spina bifida, said the planned supplements would reduce the number of babies born with neural tube defects. He claimed the campaign against them was being funded for commercial reasons.
NZPA