Iron deficiency and cognitive achievement among school-aged children and adolescents in the United States.

CONTEXT Iron deficiency anemia in infants can cause developmental problems. However, the relationship between iron status and cognitive achievement in older children is less clear. OBJECTIVE To investigate the relationship between iron deficiency and cognitive test scores among a nationally representative sample of school-aged children and adolescents. DESIGN The National Health and Nutrition Examination Survey III 1988-1994 provides cross-sectional data for children 6 to 16 years old and contains measures of iron status including transferrin saturation, free erythrocyte protoporphyrin, and serum ferritin. Children were considered iron-deficient if any 2 of these values were abnormal for age and gender, and standard hemoglobin values were used to detect anemia. Scores from standardized tests were compared for children with normal iron status, iron deficiency without anemia, and iron deficiency with anemia. Logistic regression was used to estimate the association of iron status and below average test scores, controlling for confounding factors. RESULTS Among the 5398 children in the sample, 3% were iron-deficient. The prevalence of iron deficiency was highest among adolescent girls (8.7%). Average math scores were lower for children with iron deficiency with and without anemia, compared with children with normal iron status (86.4 and 87.4 vs 93.7). By logistic regression, children with iron deficiency had greater than twice the risk of scoring below average in math than did children with normal iron status (odds ratio: 2.3; 95% confidence interval: 1.1-4.4). This elevated risk was present even for iron-deficient children without anemia (odds ratio: 2.4; 95% confidence interval: 1.1-5.2). CONCLUSIONS We demonstrated lower standardized math scores among iron-deficient school-aged children and adolescents, including those with iron deficiency without anemia. Screening for iron deficiency without anemia may be warranted for children at risk.