Anencephalus and dietary intakes.

The strong social correlations and the character istic temporal and spatial variations in the incidence of neural tube defects have suggested the existence of important environmental determinants. The most promising interpretations concerning their exact nature focus upon infective, toxic, and diet deficiency causes, the last two being supported by experimental teratogenic effects in animals. The infective hypothesis has had little support, either from experimental work or from observations in man; in particular, neural tube defects have failed to show space-time interactions of the kind expected from a smouldering infective process (such as hepatitis), or the acute epidemic forms associated with infectious fevers, influenza, and other droplet spread illnesses. A dietary association could be either a deficiency or a toxic effect. We would expect a deficiency to be manifest as a negative association between the occurrence of disease and an appropriate dietary intake for a relatively long period preceding the time of the presumed teratogenic effect. Most deficiencies would be expected to have accumulated over several months at least. A toxic dietary effect might also take time to accumulate, when the temporal pattern would be similar, although with a positive rather than a negative correlation coeffi cient. However, acute toxic effects would have a relatively precise positive chronological association, presumably six to eight months before delivery. The objective of this study is a search for correlations of these types.