Their new report looked in detail at neural tube defects (NTDs) in New Zealand, which formed the basis for recommending folic acid fortification for bread.
The most recent data showed that in 2013, 18 babies were born with NTDs and six were stillborn with an NTD.
Furthermore, since NTDs can be detected by ultrasound scans during pregnancy, many pregnant women in such a situation chose to terminate their pregnancies, a practice that has been recorded since 2008.
Including terminations, a total of 51 pregnancies were affected by NTDs in New Zealand in 2013. The authors added: "These figures are likely to be underestimates as they exclude spontaneous miscarriages, of which a proportion could be due to NTDs.
"Ethnicity data are only available for NTD live births; combined data from 2000 to 2015 show that Māori (but not Pacific) women have a higher live birth prevalence of NTDs (4.58/10,000 live births) compared to New Zealand European and other women (2.81/10,000 live births).
"Only 16% of New Zealand women of childbearing age had blood folate levels above the World Health Organization recommended level for being at minimal risk of having an NTD-affected pregnancy.”
Too little, too late?
The report then stated that there was "overwhelming evidence" that folic acid supplementation before and during early pregnancy could prevent "many cases of NTDs".
Presently, New Zealand's Ministry of Health has in place a policy for women planning to conceive, recommending that they start taking 800µg of folic acid at least four weeks before conception, continuing through to the first trimester.
However, many women tend not to do so, largely because about 40% of pregnancies in New Zealand are unplanned.
This is compounded by NTDs typically occurring within the first few weeks of pregnancy, before most women are aware of their condition or have seen a doctor about it.
As such, taking folic acid supplements only upon confirmation of pregnancy may be too late to lower the risk of NTDs developing.
Tried and tested
The authors added that in countries where mandatory folic acid fortification of staple food had been implemented and assessed, rates of NTD-affected pregnancies had dropped.
They wrote: "Analyses from 2012 suggest that moving from a hypothetical voluntary programme in which 50% of all packaged bread in New Zealand is fortified, to a mandatory programme in which 100% of packaged bread is fortified, would prevent approximately five to 15 extra NTD pregnancies annually.
"These figures may be an underestimate for the present situation in New Zealand, as less than half of packaged bread is currently being fortified."
New Zealand has been late to the fortification scene, introducing voluntary folic acid fortification of bread in 2012 as opposed to the originally planned mandatory fortification in 2007.
Doubts and assurances
Despite this, there are concerns about increased cancer risk associated with folic acid intake, stemming mainly from studies involving high-dose folic acid supplementation being linked to increased cancer and cognitive impairment risk.
Adverse effects on children whose mothers took folic acid supplements during pregnancy, as well as possible adverse effects of excessive folic acid intake not metabolised by the body into folate, have also led to folic acid's benefits being questioned.
However, University of Auckland Emeritus Professor Robert Beaglehole, the report's co-author, said the risk was inconsequential in light of the birth defects folic acid fortification could help to prevent.
He added that mandatory folic acid fortification of bread could result in an estimated 10 fewer infants born with neural tube defects, such as spina bifida.
Former Chief Science Advisor Sir Peter Gluckman agreed, saying there was an extremely low chance of developing cancer from folic acid consumption.
He further mentioned 'indirect evidence' from genetic studies that found folic acid intake could reduce overall cancer risk, though the balance among different types of cancer could change.
For instance, breast cancer risk could be lowered while prostate and colon cancer risk could be raised slightly.
He added that even with all packaged bread fortified, those at risk would not want for alternatives, which is one of the reasons the fortification of packaged bread was recommended, but not that of artisan bread or flour in general.
Read the full report here.