The research - published online in 21 April 2005 edition of the American Journal of Medical Genetics - set out to examine whether the recent decline in children born with neural tube defects in Chile was due to the addition of folic acid to wheat flour.
Data recently published in Chile suggested that the incidence of spina bifida and anencephaly - a fatal condition that results in malformation of the brain - have significantly declined since January 2000, when wheat flour began to be fortified with folic acid. During this period, Chile has been fortifying its foods at double the rate of the US.
Researchers - led by Eduardo Castilla from the genetics department at the Instituto Oswaldo Cruz in Rio de Janeiro, Brazil - investigated data from Chilean maternity hospitals, collated between 1982 and 2002 - before and after fortification.
They found that while the prevalence rates of neural tube defects did not significantly change between the two pre-fortified periods, the rate of spina bifida decreased by 51 per cent and the rate of anencephaly decreased by 46 per cent in the 2001-2002 period, hence after fortification.
According to the authors, one of the main strengths of the study is that because abortion is illegal in Chile, the data contain virtually all cases of neural tube defects.
Based on their comparison of two pre-fortification periods, the authors concluded that "neural tube defect prevalence rates were not decreasing in Chile before the start of folic acid fortification in the year 2000."
Trials first showed more than a decade ago that folic acid can reduce the occurrence of neural tube defects, such as spina bifida, by half or more. This prompted some countries, including the US, Canada and Chile, to introduce mandatory fortification of flour with folic acid.
The initiatives have paid off. In Canada, which introduced folic acid fortification in 1998, the prevalence of neural-tube defects among both unborn and newborn children has been halved and it has also had a similar benefit on incidence of the deadly childhood cancer neuroblastoma.
Each year about 3 per cent of all new births around the world are affected with major structural birth defects - or more than 4 million each year - and these are the major cause of infant mortality and disabilities among children in industrialized countries.
However Europe remains fearful of possible side-effects of a wide-ranging fortified food initiative. A two-year investigation into flour fortification by the UK's Food Standards Agency concluded in 2002 that this could mask a deficiency of vitamin B12 in elderly people.
Flour fortification rather than supplementation is preferred by many experts, who believe the whole population can be targeted rather than more privileged groups who decide to supplement their diet.