Statistics

Psychiatry

Percentile

Internal medicine

Intelligence quotient

Cognition

Pediatrics

Prospective cohort study

Cohort study

Blood lead level

CATS

Cord blood

Lead poisoning

Lead exposure

Mathematics

Wechsler Preschool and Primary Scale of Intelligence

Medicine

Cohort

Wechsler Intelligence Scale for Children

Wechsler Adult Intelligence Scale

Environmental Research

Low-level lead exposure during childhood is associated with deficit in child IQ. However, the association between prenatal lead exposure and child IQ remains inconsistent. The objective of our study was to examine the association between prenatal/postnatal lead exposure and child IQ at the age of 12. We obtained data pertaining to cord-blood and child-blood lead levels and IQ for 286 children from a prospective birth cohort study (Tohoku Study of Child Development). IQ was assessed using the Wechsler Intelligence Scale for Children-Fourth Edition. Simultaneously, the Boston Naming Test (BNT) was used to assess the children's language ability. The median lead level in the cord blood was 0.8 μg/dL (5th-95th percentiles, 0.4–1.4 μg/dL), and that in the blood of 12-year-old children was 0.7 μg/dL (0.4–1.1 μg/dL). IQ and BNT scores were significantly lower in boys than in girls; therefore, multiple regression analysis was conducted separately for boys and girls. Among boys, IQ was associated with child-blood lead (B = −16.362, p = 0.033) but not cord-blood lead (B = −6.844, p = 0.309). When boys were divided into four groups according to the child-blood lead levels, there was a significant decreasing trend for IQ. The score with cues of the BNT was associated with both cord-blood (B = −5.893, p = 0.025) and child-blood (B = −7.108, p = 0.022) lead concentrations in boys. Among girls, there was no significant association of the outcomes with cord-blood or child-blood lead level. These findings suggest that postnatal lead exposure adversely affects the intellectual ability in boys. Furthermore, the language ability is sensitive to prenatal/postnatal lead exposure in boys.

Prenatal and postnatal lead exposures and intellectual development among 12-year-old Japanese children