Cumulative childhood lead exposure estimation and school-age IQ in a prospective birth cohort

Lead is a well-known neurotoxicant with no identified safe level. Prior studies found that childhood lead exposure is associated with decreased intelligence quotient (IQ) scores. However, most studies rely on a limited number of blood lead measurements. In this prospective pregnancy and birth cohort, we estimated cumulative childhood lead exposure using repeated blood lead concentrations and regression calibration, allowing for more accurate assessment of lead burden over time and its association with IQ.

This prospective study included 262 mother-child dyads from Greater Cincinnati enrolled in the Health Outcomes and Measures of the Environment (HOME) Study from 2003 to 2006. We obtained serial blood lead measurements and estimated cumulative childhood lead exposure using a regression calibration method. Outcome was assessed via Wechsler-based IQ testing at ages 5-12 years. We examined the association between estimated cumulative childhood lead exposure and child IQ using linear regression models.

Our cohort had low levels of estimated lifetime average lead exposure (geometric mean: 1.21 μg/dL). Overall, estimated lead exposure decreased from age 12 months to time of IQ test. Cumulative childhood lead exposure estimate was associated with decreased IQ at ages 5-12 years in unadjusted analyses, but not after adjusting for maternal IQ, household income, reported prenatal vitamin use, Home Observation for Measurement of the Environment score, and maternal serum cotinine. Sensitivity analyses additionally adjusting for prenatal total folate did not markedly change our results. We assessed early-life, school-age, or concurrent blood lead exposure estimate in place of cumulative childhood lead exposure estimate and observed a similar pattern of results.

We used a regression calibration method to leverage robust, repeated lead exposure data in our prospective pregnancy and birth cohort. In this cohort with low levels of lead exposure, cumulative childhood lead exposure estimate was negatively associated with school-age IQ in unadjusted analyses but not adjusted analyses. We considered sociodemographic and maternal factors previously associated with cognitive development. Our results suggest these factors may confound the association between low-level child lead exposure and child IQ.