The study, published in BMC Pregnancy and Childbirth, showed that the proportion of babies born with neural tube defects in the province of Newfoundland and Labrador, Canada, dropped by 78 per cent after the Canadian government ruled that folic acid must be added to flour, cornmeal and pasta.
The researchers - led by Dr Catherine McCourt, from the population and public health branch of Health Canada - found that women of childbearing age who ate the fortified food increased their dietary intake of folic acid by an average of 70 micrograms a day. Their blood folate levels also increased significantly.
Since fortification in 1998, the incidence of neural tube defects in this province has reduced from an average of 4.36 defects per 1000 births to an average of 0.96 defects per 1000 births.
Moreover, during this period, the number of women aged between 19 and 44 who took folic acid supplements rose significantly from 17 per cent to 28 per cent.
However, the researchers were not able in this study to determine the separate contributions of food fortification and supplement use in the decline of neural tube defects.
The authors therefore concluded that: "public education regarding folic acid supplement use by women of childbearing age should continue."
Furthermore, they noted that they found no evidence during this study of a deterioration in vitamin B12 status in this age group and no evidence that improved levels of blood folate masked this vitamin deficiency, as some research has suggested.
Folic acid fortification has proven its value in reducing birth defects in the US too, but in Europe governments have been reluctant to implement similar initiatives. The UK's Food Standards Agency last year decided against fortification on the grounds that not enough was known about the potential adverse effects on older people. Campaigners in Switzerland have also met with resistance.
However, attitudes in the food industry seem to be changing. A meeting organised by the Flour Fortification Initiative (FFI) in London in June raised support for flour fortification among industry members.
"Since talking to the millers seriously about this issue, they seem very motivated and really want to contribute," said the head of the FFI, Professor Glen Maberly based at Emory University in the US.
Nontheless, cost and technical issues still present concerns for the industry. Flour fortification means buying nutrients, new equipment, further testing and quality control, and marketing spend. With little government support, both the private sector and consumers must bear some of these additional costs.
But better dissemination of technical expertise across borders and increased knowledge about fortification could help to reduce some of these costs and make the process more efficient.