Efficacy of iron and/or zinc supplementation on cognitive performance of lead-exposed Mexican schoolchildren: a randomized, placebo-controlled trial.

OBJECTIVE: Lead exposure in children has been associated with both global and specific cognitive deficits. Although chelation therapy is advised for children with blood lead concentrations of >44 microg/dL, treatment options for children with lower blood lead values are limited. Because lead absorption is related to children's nutritional status, micronutrient supplements may be 1 strategy for combating low-level, chronic lead exposure. This study was designed to test the efficacy of iron and zinc supplementation for lowering blood lead concentrations and improving cognitive performance in schoolchildren who live in a lead-contaminated city. METHODS: This randomized, double-blind, placebo-controlled field trial was conducted in public elementary schools in Torreón, an industrialized city in northern Mexico. A metal foundry, located close to the city center and within 3.5 km of 9 schools, was the main source of lead exposure. A total of 602 children who were aged 6 to 8 years and regularly attending first grade in the study schools were enrolled. Children were given 30 mg of iron, 30 mg of zinc, both, or a placebo daily for 6 months. A total of 527 completed the treatment, and 515 were available for long-term follow-up, after another 6 months without supplementation. Eleven cognitive tests of memory, attention, visual-spatial abilities, and learning were administered at baseline and each follow-up. RESULTS: There were no consistent or lasting differences in cognitive performance among treatment groups. CONCLUSIONS: Daily supplementation with iron and/or zinc may be of limited usefulness for improving cognition in lead-exposed schoolchildren. However, these treatments may be effective in settings with higher prevalence of nutritional deficiencies or in younger children.

Deficits in cognitive function and achievement in Mexican first-graders with low blood lead concentrations.

Elevated blood lead levels in children are associated with lower scores on tests of cognitive functioning. Recent studies have reported inverse relations between lifetime exposure and intellectual functioning at blood lead concentrations below 10 microg/dL, the Centers for Disease Control and Prevention's (CDC) level of concern. We report associations between blood lead and cognitive performance for first-grade Mexican children living near a metal foundry. Using a cross-sectional design, we examined the relation between children's concurrent blood lead concentrations (mean (SD) 11.4 microg/dL (6.1)) and their performance on 14 tests of global or specific cognitive functions. The blood lead-cognition relations were modeled using both linear and nonlinear methods. After adjustment for covariates, a higher blood lead level was associated with poorer cognitive performance on several cognitive tests. Segmented linear regressions revealed significant effects of lead but only for the segments defined by a concurrent blood lead concentration below 10-14 microg/dL. One implication of these findings is that at the age of 7 years, even in the absence of information on lead exposure in infancy and early childhood, a test result with blood lead < 10 microg/dL should not be considered safe. Together with other recent findings, these results add to the empirical base of support available for evaluating the adequacy of current screening guidelines and for motivating efforts at primary prevention of childhood lead exposure.

Iron and zinc supplementation does not improve parent or teacher ratings of behavior in first grade Mexican children exposed to lead.

OBJECTIVE: To determine the efficacy of iron and zinc supplementation on behavior ratings of lead-exposed children. STUDY DESIGN: In this double-blind, randomized trial, 602 first-grade children received 30 mg ferrous fumarate, 30 mg zinc oxide, both, or placebo daily for 6 months. Lead, iron, and zinc status were determined at baseline and follow-up. Parents and teachers provided ratings of child behavior using the Conners Rating Scales. RESULTS: The baseline mean (SD) blood lead concentration was 11.5 (6.1) mug/dL, with 51% of children > or = 10 microg/dL. The prevalence of attention deficit hyperactivity disorder, estimated by combined parent and teacher ratings, was 6%. At follow-up, parent ratings of oppositional, hyperactive, cognitive problems, and attention deficit hyperactivity disorder decreased by 1.5, 1.2, 2.5, and 3.4 points, respectively (P < .05). Teacher ratings of hyperactivity increased by 1.1 points (P = .008), and the mean cognitive problem score declined by 0.7 points (P = .038). There were no treatment effects on mean change in scores, but children receiving any zinc had a higher likelihood of no longer receiving clinically-significant teacher ratings of oppositional behaviors. CONCLUSIONS: This regimen of supplementation did not result in consistent improvements in ratings of behavior in lead-exposed children over 6 months.