The results have implications on both sides of the Atlantic, with some in North America calling for an increase in the level of fortification, while European countries continue to debate the issue.
Folate is found in foods such as green leafy vegetables, chick peas and lentils, and an overwhelming body of evidence links has linked folate deficiency in early pregnancy to increased risk of neural tube defects (NTD) - most commonly spina bifida and anencephaly - in infants.
This connection led to the 1998 introduction of public health measures in the US and Canada, where all grain products are fortified with folic acid - the synthetic, bioavailable form of folate.
While preliminary evidence indicates that the measure is having an effect with a reported 15 to 50 per cent reduction in NTD incidence, parallel measures in European countries, including the UK and Ireland, are still on the table.
The new study, published in the current issue of The Journal of Nutrition (Vol. 136, pp. 2820-2826), looked at the effects of fortification on the folate intake of 61 university-educated women (average age 32) during pregnancy (recruited at week 36) and lactation (four and 16 weeks of lactation) based on weighed food records.
The researchers, led by Kelly Sherwood and Deborah O'Connor from the University of Toronto found that the average dietary folate intake during pregnancy was 562 micrograms per day, while average intake during lactation was 498 micrograms per day.
Taking the estimated average requirement of the women as 520 micrograms per day, Sherwood and her co-workers report that 36 per cent of the women were not getting adequate folate intakes during pregnancy, a figure which fell to 32 per cent during lactation.
"Assuming folic acid is being added to the food supply at mandated levels, approximately one-third of our sample of highly educated late pregnant and lactating women from high-income households did not meet their requirement for folate from diet alone," said Sherwood.
While these results may suggest to some that the folate fortification is inadequate, the researcher point out that without fortification 98 per cent of the women would failed to meet their requirements.
The researchers calculated that if the level of fortification was doubled to 280 to 300 micrograms per 100 grams of grain, then the average intakes during pregnancy and lactation would increase to 786 and 716 micrograms per day, respectively.
This would mean that only three per cent of the population would have inadequate folate intakes.
However, such a measure has its disadvantages with some sections of the population at risk of getting too much folate. The main reason not to proceed that is cited by those not in favour of fortification is that upping folate levels across the entire population may mask a form of anaemia in elderly people that is caused by vitamin B12 deficiency, and can cause dementia.
Indeed, Sherwood and co-workers note: "Fortifying food at double the currently mandated level may put non-target groups in danger of over consumption."
Such observations appear to support the combination of supplements with the existing levels of fortification. Moreover, when the researchers calculated the effect of a daily 400 micrograms folic acid supplement, the prevalence of inadequacy fell to zero.
"Given the role of folate in the prevention of neural tube defect, health care professionals need to continue to use recommended tools of improving the folate intakes of lactating women capable of becoming pregnant, including educating them about food rich in folate and encouraging the use of a folate acid-containing supplement" they said.
A flip-side to the fortification debate was highlighted recently when Swedish scientists reported that people with low folate levels may actually be at a lower risk of colorectal cancer, a result that appeared to go against the grain of other studies that had reported potential benefits in this area.
The researchers of that study, published in the October issue of Gut (Vol. 55, pp. 1461-1466) said that their results could have implications for the fortification debate.
In the UK, the Food Standards Agency's Scientific Advisory Committee on Nutrition has asked the board for more time before delivering its final report on the fortification question. A spokesperson for the FSA told NutraIngredients.com in May that the ongoing investigations relate to increasing folate intake over 1mg per day.
In July Ireland's National Committee on Folic Acid Fortication today recommended that most In July white, brown and wholemeal breads sold in the country be fortified with 120 micrograms of folic acid per 100g of bread - a move which will require legislative change and minor modifications to the bread-making process.
Food Standards Australia New Zealand (FSANZ) has also embarked on the path towards fortification, last month calling for public comment on a proposal that would require all bread-making flour to be fortified with folic acid.
The study of Sherwood and co-workers was funded by Merck KgaA and the Natural Sciences and Research Council of Canada.