Vitamin deficiencies and neural-tube defects: human and animal studies.

The evidence for an association between vitamin deficiency in early pregnancy and the prevalence of neural-tube defects in humans is reviewed, with particular emphasis on the methodological problems encountered in conducting such studies. It is apparent that there is strong evidence for an association between maternal vitamin status and the outcome of pregnancy, but this is not universally accepted, due to ethical and practical constraints on the design of the studies. There are also problems in obtaining precise information from experiments on animals in vivo. By culturing rat embryos in dialysed serum in which the micromolecular component is defined, it has been possible to demonstrate that significant numbers of neural-tube defects can be produced by the deficiency of a single vitamin (inositol), and that multiple vitamin deficiency produces a further significant increase in the frequency of such defects.