Early-Life Low Lead Levels and Academic Achievement in Childhood and Adolescence.

Importance: In 2021, the Centers for Disease Control and Prevention lowered the blood lead reference values to 3.5 μg/dL or higher. More evidence is needed on the association between lead changes below 3.5 μg/dL and academic achievement. Objective: To examine the association of a 1-unit change in early childhood blood lead levels below 3.5 μg/dL vs at 3.5 μg/dL or higher with academic achievement. Design, Setting, and Participants: This cohort study linked birth certificates of children born in Iowa from 1989 to 2010 to their math and reading test scores for grades 2 through 11 and to their early childhood blood lead testing data. Analyses were completed between May 2024 and March 2025. Exposures: Early life blood lead levels below 3.5 μg/dL and at 3.5 μg/dL or higher. Main Outcome and Measure: The primary outcome was national percentile rank (NPR) scores on math and reading school tests. Regression models estimated the association between lead levels and math and reading scores, controlling for sociodemographic, child and maternal health, and school characteristics. Results: The analytical sample included up to 305 256 children and 1 782 873 child-grade observations. Within the analytical sample, 51.0% were male, 41.1% were first-born children, and 43.9% were born to mothers with an educational level of high school or less. Sociodemographic and child and maternal health characteristics were similar between the analytical sample and the birth population. The mean (SD) child age at lead testing was 1.9 (1.5) years. Among these children, 37.7% had lead values below 3.5 μg/dL. A 1-unit increase in lead levels below 3.5 μg/dL was associated with lower NPR scores in math by -0.47 (95% CI, -0.65 to -0.30) and in reading by -0.38 (95% CI, -0.56 to -0.20). For lead levels at 3.5 μg/dL or higher, a 1-unit increase in lead levels was associated with lower NPR scores in math by -0.52 (95% CI, -0.58 to -0.47) and in reading by -0.56 (95% CI, -0.62 to -0.51). These score declines were persistent across grades 2 through 11. Conclusions and Relevance: In this cohort study assessing early life low lead level and children's and adolescents' academic achievement, a 1-unit increase in lead levels in the range currently considered low for further interventions was associated with worse academic performance throughout school grades comparable to that for lead levels in the range recommended for additional interventions. These findings support the need to reconsider and potentially lower current blood lead reference values for recommending further interventions.