Impact of Low Blood Lead Concentrations on IQ and School Performance in Chinese Children

OBJECTIVES Examine the relationships between blood lead concentrations and children's intelligence quotient (IQ) and school performance. PARTICIPANTS AND METHODS Participants were 1341 children (738 boys and 603 girls) from Jintan, China. Blood lead concentrations were measured when children were 3-5 years old. IQ was assessed using the Chinese version and norms of the Wechsler Preschool and Primary Scale of Intelligence - Revised when children were 6 years old. School performance was assessed by standardized city tests on 3 major subjects (Chinese, Math, and English [as a foreign language]) when children were age 8-10 years. RESULTS Mean blood lead concentration was 6.43 µg/dL (SD = 2.64). For blood lead concentrations, 7.8% of children (n = 105) had ≥10.0 µg/dL, 13.8% (n = 185) had 8.0 to <10.0 µg/dL, and 78.4% (n = 1051) had <8.0 µg/dL. Compared to children with blood lead concentrations <8 µg/dL, those with blood lead concentrations ≥8 µg/dL scored 2-3 points lower in IQ and 5-6 points lower in school tests. There were no significant differences in IQ or school tests between children with blood lead concentrations groups 8-10 and ≥10 µg/dL. After adjustment for child and family characteristics and IQ, blood lead concentrations ≥10 µg/dL vs <8 µg/dL at ages 3-5 years was associated with reduced scores on school tests at age 8-10 years (Chinese, β = -3.54, 95%CI = -6.46, -0.63; Math, β = -4.63, 95%CI = -7.86, -1.40; English, β = -4.66, 95%CI = -8.09, -1.23). IQ partially mediated the relationship between elevated blood lead concentrations and later school performance. CONCLUSIONS Findings support that blood lead concentrations in early childhood, even <10 µg/dL, have a long-term negative impact on cognitive development. The association between blood lead concentrations 8-10 µg/dL and cognitive development needs further study in Chinese children and children from other developing countries.