Folic acid, which has been proven to prevent serious birth defects, is set to be added to bread.
The announcement was made Thursday morning.
"This is about protecting babies," said Food Safety Minister Dr Ayesha Verrall. "Low folate levels in mothers cause neural tube defects that result in the death of babies, or lifelong disability."
Folic acid, a B vitamin also known as folate, was set to be added to bread in 2009 under a joint Australia-New Zealand plan negotiated by the previous Labour-led Government, but it was scrapped by National.
In 2012 new research showed since mandatory fortification of bread, pasta and cereal in the US, there had been a significant decline in childhood brain and kidney tumours - even more so in newborn infants.
But Food Safety Minister at the time, Kate Wilkinson, sided with the food industry, which said fortification would be costly. The NZ Organisation for Rare Disorders at the time said the decision would condemn 20 babies a year to either serious disability - this was backed up in 2019 when the Ministry for Primary Industries estimated up to 171 neural tube defects in babies such as spina bifida could have been prevented if the 2009 policy had gone ahead.
Australia went ahead with fortification, and saw a significant drop in the number of defects.
In 2020 the College of Public Health Medicine said an additional 200 miscarriages a year were likely happening because New Zealand, unlike dozens of other countries, hadn't fortified bread with folic acid.
There were concerns expressed that making folic acid a mandatory ingredient in bread would amount to mass medication.
"Folate is naturally present in food," said Dr Verrall. "Folic acid fortification restores what is lost during processing such as flour milling."
While many mothers-to-be take folic acid supplements, the most important time to be taking it is in the first few weeks of a pregnancy - when many women don't realise they're pregnant.
A 2018 report by the Office of the Prime Minister's Chief Science Advisor said there was "compelling evidence" in favour of mandatory fortification, the benefits far outweighing the potential risks. Despite the evidence, National last year said it remained opposed to mandatory fortification.
Millers will reportedly get $1.6 million for the necessary equipment. The policy will be phased in over two years.