Developmental sequel from early nutritional deficiencies: conclusive and probability judgements.

Results from quasi-experimental longitudinal studies of children and from experimental research with animal models have led several investigators to state that early iron deficiency anemia leaves a permanent cognitive deficit. However, neither source of information provides a basis for such a claim. Some key confounders were not controlled by the quasi-experimental studies, and the external validity of the animal data is questionable. Further, three decades of research on the functional consequences of protein-energy malnutrition have shown that the social environment moderates the effects of an early nutritional insult; it can keep such effect unchanged, or increase or decrease its severity. The prediction of later life on the basis of a particular nutritional event carries a large error factor, which suggests that the search would be more fruitful if we tracked probability statements.