The Minister of Food Safety has spoken out strongly against the imminent compulsory addition of folic acid to most bread.

"I'm not a fan," Kate Wilkinson said yesterday of the transtasman food standard that requires the synthetic vitamin be added to virtually all bread from September. "I sympathise with the bakers' frustration."

Her Labour predecessor, Annette King, agreed to the rule's introduction by the Food Standards Australia New Zealand agency, and although Ms Wilkinson is looking into seeking a review, officials have told her that pulling out of the scheme could adversely affect transtasman relations.

Ms Wilkinson, who began investigating the matter after lobbying by bakers, said a review by the food agency would be a prolonged process.

The Cabinet was still considering official advice before deciding what to do. She said Ms King should have opted for voluntary fortification of foods. This is the existing regime.

Under the new rule, all commercially baked bread, except organic bread, must contain 80 to 100 micrograms of folic acid per 100g of bread.

Women can cut the risk of babies having neural-tube defects such as spina bifida if they take in adequate folic acid in the weeks before conception and during early pregnancy.

The food agency predicts mandatory fortification of bread with folic acid at the level it has stipulated will reduce the number of births affected by neural tube defects by four to 14 a year.

The Ministry of Health says that despite the mandatory fortification, women planning a pregnancy will still need to take a folic acid supplement for at least a month before conception and 12 weeks afterwards.

Bakers have characterised mandatory fortification as "mass medication" and want the voluntary regime kept.

Jim Mann, Otago University's professor of human nutrition and medicine, said he was initially unenthusiastic about mandatory addition of folic acid to the food supply, but was now a supporter.

He urged monitoring of the elderly, however, to pick up any masking of vitamin B12 deficiency, which, if undetected, could lead to neurological damage.

He said that even though the level of fortification under the standard would not provide all the folic acid needed before and during pregnancy, there would be an incremental benefit.

Asked about reports that folic acid was associated with an increased risk of colon cancer, he indicated it was a very minor consideration compared with risk factors such as obesity and lack of physical activity.

WHAT IS IT

* Folic acid is man-made folate.

* Folate is an essential B vitamin found in foods, including leafy vegetables, citrus fruits and wholemeal bread.

* New Zealand adults consume about 250 micrograms a day.

* Recommended intake is 400 mcg; 600mcg for pregnant women; 500mcg while breastfeeding.

* Adequate intake reduces risk of babies being born with neural-tube defects, including spina bifida.

* The Government is assessing the latest scientific evidence on risks and benefits of mandatory folic acid fortification of bread.

* The US requires fortification of all cereal/grain flours and Canada of white flour and pasta.