Fetal Lead Exposure and Hyperactivity at 24 Months of Age

Abstract

ISEE-323 Objective: Previous reports have linked exposure to lead and attention-deficit hyperactivity disorder (ADHD) in children; however, no studies have assessed the effect of prenatal lead exposure on signs of hyperactivity at a young age. In this study, we assess the relationship between prenatal lead exposure, as measured by maternal bone lead concentration and child hyperactivity at age 24 months. Material and Methods: We studied 759 children participating in 3 cohort studies in Mexico City, enrolled and followed up between 1993 and 2004. Maternal bone Pb concentrations were measured in tibia and patella 1 month after delivery using a 109Cd K-XRF instrument. The primary outcome variable was the 5-category Hyperactivity (behavior that is superfluous and impulsive) item of the Bayley Scales of Infant Development II (BSID-II) Behavior Rating Scale applied at age 24 months. Ordinal logistic regression models were fitted to the data. Adjusted odds ratio (OR) estimates were obtained, controlling for gender, maternal intelligence, birth cohort, and the psychomotor (PDI) and mental (MDI) development indices of the BSID-II. Results: We found that a 10 ppm increase in tibia Pb concentration is associated with a 36% increase in the odds of scoring worse in the hyperactivity item of the BSID-II (OR = 1.36, P = 0.03). Patella lead concentrations were not associated with hyperactivity. The MDI was the strongest determinant of hyperactivity; greater mental development is associated with lower odds of hyperactivity signs, a standard deviation increase in MDI is associated with a 53% reduction in the odds of scoring worse in the hyperactivity item (P < 0.01). Conclusions: We conclude that fetal exposure to lead may be an important determinant of hyperactive behavior at age 24 months. Studies linking fetal lead exposure and behavior at later ages will be important to determine whether fetal lead exposure is a risk factor for ADHD or other behavioral problems.