De Wals P et al. (2007) Reduction in neural-tube defects after folic acid fortification in Canada. N Engl J Med 357: 135–142

Folic-acid supplementation during the periconceptive period reduces the risk of neural-tube defects in offspring. In 1998, the folic-acid fortification of certain cereal products became mandatory in Canada. Now, De Wals and colleagues report that the prevalence of neural-tube defects in the Canadian population has fallen following implementation of this regulation.

Among the 1,909,741 births (including still births and terminations because of fetal abnormalities) that occurred in seven Canadian provinces during the period 1993–2002, the researchers identified 2,446 subjects with neural-tube defects. On the basis of previously published results showing that red-cell folate levels started to rise in the Canadian population in April 1997, reaching a plateau in February 1999, the study period was divided into three phases: prefortification (before September 1997), partial-fortification (October 1997 to March 2000), and full-fortification (April 2000 onwards). The prevalence of neural-tube defects markedly decreased from 1.58 per 1,000 births in the prefortification phase, to 0.86 per 1,000 births in the full-fortification phase. The magnitude of the decrease in the prevalence of spina bifida (53%) was greater than that for anencephaly (38%) or encephalocele (31%). Historically, the prevalence of neural-tube defects has been higher in the eastern than in the western provinces of Canada. The researchers found that the greatest decreases in the prevalence of neural-tube defects occurred in the eastern provinces that had the highest prefortification prevalences, and as such, geographical differences in the prevalence of neural-tube defects almost disappeared after the full implementation of folic-acid fortification.