Early exposure to lead, whether in utero or as a young child, may cause lasting harm in a child's cognitive (brain) development.

In a British Medical Journal editorial examining the effects of lead on children's intelligence, author M. R. Moore, Emeritus Professor of Occupational Health at the University of Manchester, pointed to a recent follow up of American children who in 1979 had been part of a study examining the relationship between the level of lead in milk teeth and learning abilities.
Even though they had not suffered more recent exposure to lead, those children with higher levels of lead in their milk teeth were more likely to drop out of high school or to have reading disabilities, lower vocabularies and lower grammatical/reasoning scores.

Furthermore, the subgroup that had been reexamined after 11 years were among those who had had lower concentrations of lead in their teeth.
Other studies pointed to a relationship between the concentration of lead in the umbilical cord and a decrease in mean intelligence of the child in later life.
Professor Moore cited several other studies from around the globe that supported this American study by Needleman et al. 'Among the variables that have been explored,' he said, 'one interesting and important interaction has emerged. Children from famlies in the lower socioeconomic groups seem more vulnerable to the effects of lead than children from more favoured backgrounds.'

That observation jibed with the results of an Australian study, showing no relationship between psychological development and blood lead concentrations among children from well educated, middle-class families.

Scratching around for an explanation, Moore wondered, 'Do disadvantaged and less able children play outside in the dirt and ingest more lead while their more literate brethren stay indoors to read? What Moore seemed unwilling to raise was the possible protective role that a good diet might play in protecting children from lead exposure. Such a relationship was suggested in a study published by Ward et al in the Journal of Nutritional Medicine, which found that high levels of lead and correspondingly low levels of zinc in the mother had an effect on the growth of the fetus. - British Medical Journal, 15 September 1990.