In a joint agreement with Australia, New Zealand decided to adopt a mandatory policy in 2007, under the Labour-led Government.
After an often-fraught public debate marred by scaremongering about the risks of folic acid consumption, the National-led Government decided not to proceed with it and introduced a voluntary policy in 2012.
The Prime Minister's chief science advisor Sir Peter Gluckman slammed the Government's decision, saying it was not underpinned by science.
Under the voluntary folic acid regime, the Ministry for Primary Industries and producers have set a goal of 50 per cent fortification of sliced, packaged bread.
Bennett said supermarkets were making "reasonable progress" towards the target. Since 2012, the level of fortification of packaged, sliced bread had risen from 14 per cent to 32 per cent.
It is understood that New Zealand has also had a reduction in neural tube defects under the voluntary regime, but not to the same extent as Australia.
The minister, who took over the portfolio in December, said there were some uncertainties about the new Australian research. Neural tube defect rates may have already been falling, and there are question marks over whether the benchmark data was robust.
"But the initial results were positive about its introduction and the effect they've seen in their communities, especially at-risk communities."
The Government was swayed away from a mandatory policy after a campaign by the food industry and fears about the links - later dismissed by the chief science advisor - between folic acid fortification and cancer.
One of the most vocal opponents of New Zealand's mandatory policy in 2012 was the influential Food and Grocery Council, which represents food producers. Chief executive Katherine Rich said yesterday that the voluntary scheme had "performed very well".
She reiterated the council's opposition: "The idea of dosing the entire food supply so that it ups the level for everybody means that in some cases people will be consuming too much".
A report by Sir Peter in 2013, however, underlined the benefits of folic acid fortification, saying there was "a strong consensus that [folic acid] is safe and effective in reducing the incidence of neural tube defects in newborns".
Asked whether he feared a public or industry backlash over any folic acid changes, Bennett said his main priority was on the health of mothers and children. He added that the debate over whether bread should include folic acid Australia was not as tense as in New Zealand.
"There wasn't any public debate around its effectiveness," he said.
A New Zealand Medical Journal article published in 2014 criticised the decision to abandon a mandatory regime in New Zealand, saying 100 cases of serious disability or deaths could have been avoided over five years.
Around 80 babies a year are seriously disabled or killed by neural birth defects in New Zealand, and studies predicted that 24 of these cases would be prevented by mandatory fortification.
The NZMJ article cited data which showed just 2 per cent of New Zealand women checked whether bread contained folic acid, and just 14 per cent of them deliberately consumed food for its folate content.
Q&A
What is folate/folic acid?
It is an essential B vitamin which occurs naturally in some vegetables, fruits, and bread. Folic acid is the synthetic, man-made version of it which is sometimes added to bread or dietary supplements.
Do all people need it, or just pregnant mothers?
The Ministry of Health says it has benefits for all adults, because it helps with cell growth and reproduction and can prevent blood disorders.
Folic acid can also help ensure the healthy development of babies, and helps reduce defects such as spina bifida.
What is a good amount?
The ministry recommends 400 micrograms of folate a day for everyone, 500-650mcg for pregnant and breastfeeding women, and higher doses for pregnant women with risky conditions.
Three slices of bread fortified with folic acid will get you 120mcg, which is why pregnant mums are encouraged to take folic acid supplements.
Are there any risks?
Not at the recommended intake levels. The ministry says ongoing research suggests high levels of folic acid could mask vitamin B12 deficiency in the elderly and the young. But this is unlikely to occur if intake is less than 1mg a day - much higher than the recommended intake.
Why is it such a hot political issue?
The National-led Government, with support from the Greens, dropped a plan to make it mandatory to add folic acid to bread in 2012.
That was criticised by scientists and doctors who said folic acid fortification had been proven to be safe and was effective in reducing defects in newborns.
