Folic acid and human malformations: a summary and evaluation.

A large body of evidence gathered over the past 30 or more years has led to the firmly established belief that deficiency of the vitamin folic acid is a cause of congenital malformations of neural tube closure. Beginning with studies showing folic acid levels of mothers of children with such defects to be low, this belief has been solidified by epidemiologic studies revealing that this consequence is prevented by maternal supplements of the vitamin from early pregnancy. The present article reviews this evidence for the purpose of examining the claims of the efficacy of folic acid in this respect. This seems to be an advantageous moment to do so, because no clear impact of folic acid supplementation and fortification on the prevalence of neural tube defects has as yet been documented; and furthermore a pause seems to have been reached in such studies. It is felt that a historical, i.e. a chronologic approach will best describe the findings, and therefore they will be considered as they unfolded.