Folic acid will be put in bread making flour to prevent devastating birth defects that can result in death or lifelong disability, it can be revealed.

Fortifying bread and other food staples with folic acid has significantly reduced birth defects of the brain, spine, or spinal cord in other countries including the United States, Canada and Australia.

The move comes after an investigation by the Herald exposed the heartbreaking stories of parents who have been pushing for years for New Zealand to match other countries by fortifying bread.

"This is about protecting babies. Low folate levels in mothers cause neural tube defects that result in the death of babies, or lifelong disability," said Food Safety Minister Dr Ayesha Verrall.

"This B vitamin is safe and essential for health, particularly for development of babies early in pregnancy. Folate is naturally present in food - folic acid fortification restores what is lost during processing such as flour milling.

"A little over half of pregnancies in New Zealand are unplanned, so it's not practical for all women to take a folic acid supplement one month before they conceive."

The health measure is a breakthrough for New Zealand's medical and scientific communities and patient advocates, who were despondent after plans to add folic acid to bread from 2009 were upended by industry opposition claiming possible risks from "mass medication".

An illustration of spina bifida. A 'snowflake condition', it affects each person differently.

Under the policy announced today, fortification of bread making flour will happen from mid to late 2023. Organic and non-wheat flour will be exempt, which the government says will give consumers choice.

The change is expected to prevent 162-240 neural tube defects over 30 years, and save $25 million and $47 million over the same period in health, education and productivity costs. Flour millers will get about $1.6 million to buy and install the necessary equipment.

Today's announcement follows a Herald investigation that revealed the benefit could be much greater, because official estimates did not count miscarriages earlier in pregnancy. The College of Public Health Medicine believes as many as 200 such miscarriages could be prevented every year, something it called an "iceberg of heartbreak".

Our reporting also told the stories of families affected by birth defects, including a woman who lost her son to anencephaly, an unsurvivable defect where parts of the brain and skull don't develop.

Verrall told the Herald that quantifying any prevention of miscarriages in early pregnancy was tricky, given such tragedies often don't generate medical statistics.

"We made the decision to make sure we could prevent neural tube defects, and if in the course of that we happen to save some families the grief of miscarriage we'd be very happy."

An illustration of anencephaly, one of the birth defects that adequate folate consumption can reduce the risk of.

Getting enough folate, a natural B vitamin found in foods such as leafy green vegetables, before and in early pregnancy can considerably reduce the risk of such neural tube defects, the most common of which is spina bifida.

It's difficult to get enough from diet alone, and women are advised to take folic acid tablets. However, many don't, and more than half of pregnancies aren't planned - a proportion that rises for young mothers (83 per cent), Māori (75 per cent) and Pacific Kiwis (71 per cent). When those women realise they're pregnant it's often too late - the neural tube closes 15 to 28 days after conception.

For this reason, NZ and Australia agreed to mandatory fortification from 2009, but the new National Government backed out after an opposition campaign by bakers and the Food & Grocery Council (an industry lobby group), who warned of unknown effects and labelled the initiative an example of the "nanny state".

Australia went ahead, and the rate of neural tube defects dropped by another 14 per cent overall, and by 74 per cent for indigenous women and 55 per cent for teenage mothers.

New Zealand's Ministry for Primary Industries estimates up to 171 pregnancies affected by a neural tube defect could have been prevented in the decade after 2009, had mandatory fortification of bread gone ahead. More than half of such pregnancies are terminated or result in stillbirths.

A 2018 report by the New Zealand Prime Minister's chief science adviser and the Royal Society concluded unequivocal benefits of mandatory fortification of packaged bread outweigh any potential adverse health effects, with "no evidence of harmful health effects of folic acid supplementation in adults, at least at low doses in the range suggested for fortification".

"That comprehensively put to rest some of those concerns that had been raised. I have to say, I think the concerns all along have been marginal and in some cases spurious," Verrall said.

It was heartbreaking to think of the birth defects that could have been prevented, the Food Safety Minister said: "It shows the real-world impact disinformation can have."

Simon Thurston (right) and his father, Lyall Thurston, photographed in 2009. Lyall has been a driving force behind a decades-old campaign for mandatory fortification. (Photo / Alan Gibson)

Lyall Thurston has for nearly 40 years spearheaded the campaign for folate in bread, after his oldest son was born with spina bifida in the late 1980s. He told the Herald the status quo was undefendable.

"We knowingly commit kids to wheelchairs. It is bizarre. It is medical, public health malpractice."

New Zealand currently has a voluntary system that aims to have up to half of packaged bread fortified with folic acid (about 38 per cent currently is).

The Food & Grocery Council, which represents food manufacturers, wants the voluntary system to continue while more consideration is given to what it says is emerging evidence of possible health risks.

It says those risks include over-consumption of folic acid including by children, whether an elderly person with high folate but low vitamin B12 levels could have faster cognitive decline and what unmetabolised folic acid might do to the nervous system.

Those in favour of mandatory fortification include the Ministry of Health, Auckland Regional Public Health Service, DHBs, Plunket, the Medical Association, the College of Obstetricians and Gynaecologists, the Paediatric Society, College of Physicians, Nurses Organisation, College of Midwives, Dieticians NZ, Consumer NZ, scientists, health academics and workers, including doctors and midwives.

The policy won't require legislative change. National confirmed it remained opposed ahead of the last election, citing the desire to protect consumer choice.