This study examines the association between low-level environmental lead exposure and children's intellectual function, focusing on blood lead levels below 10 µg/dL. Researchers analyzed data from 1,333 children across seven international longitudinal cohort studies, tracking them from birth to age 5–10. The primary outcome was full-scale IQ, measured using standardized tests. Blood lead levels peaked at 17.8 µg/dL and declined to 9.4 µg/dL by age 5–7. Of the children, 18% had maximal blood lead levels below 10 µg/dL, and 8% below 7.5 µg/dL. After adjusting for covariates, the study found an inverse relationship between blood lead concentration and IQ scores. Using a log-linear model, an increase in blood lead levels from 2.4 to 30 µg/dL was associated with a 6.9-point decrease in IQ. The estimated IQ decrements for increases in blood lead from 2.4 to 10 µg/dL, 10 to 20 µg/dL, and 20 to 30 µg/dL were 3.9, 1.9, and 1.1 points, respectively. For children with maximal blood lead levels below 7.5 µg/dL, the lead-associated intellectual decrement was significantly greater than for those with levels ≥7.5 µg/dL (p = 0.015). The study concludes that environmental lead exposure in children with maximal blood lead levels below 7.5 µg/dL is associated with intellectual deficits. The findings suggest that even low levels of lead exposure can have adverse effects on cognitive development. The study highlights the need for further research and policy actions to reduce lead exposure, especially in children, as current blood lead levels in children are higher than those found in pre-industrial humans, and there is no clear threshold for adverse effects. The results emphasize the importance of primary prevention to mitigate the health impacts of lead exposure.This study examines the association between low-level environmental lead exposure and children's intellectual function, focusing on blood lead levels below 10 µg/dL. Researchers analyzed data from 1,333 children across seven international longitudinal cohort studies, tracking them from birth to age 5–10. The primary outcome was full-scale IQ, measured using standardized tests. Blood lead levels peaked at 17.8 µg/dL and declined to 9.4 µg/dL by age 5–7. Of the children, 18% had maximal blood lead levels below 10 µg/dL, and 8% below 7.5 µg/dL. After adjusting for covariates, the study found an inverse relationship between blood lead concentration and IQ scores. Using a log-linear model, an increase in blood lead levels from 2.4 to 30 µg/dL was associated with a 6.9-point decrease in IQ. The estimated IQ decrements for increases in blood lead from 2.4 to 10 µg/dL, 10 to 20 µg/dL, and 20 to 30 µg/dL were 3.9, 1.9, and 1.1 points, respectively. For children with maximal blood lead levels below 7.5 µg/dL, the lead-associated intellectual decrement was significantly greater than for those with levels ≥7.5 µg/dL (p = 0.015). The study concludes that environmental lead exposure in children with maximal blood lead levels below 7.5 µg/dL is associated with intellectual deficits. The findings suggest that even low levels of lead exposure can have adverse effects on cognitive development. The study highlights the need for further research and policy actions to reduce lead exposure, especially in children, as current blood lead levels in children are higher than those found in pre-industrial humans, and there is no clear threshold for adverse effects. The results emphasize the importance of primary prevention to mitigate the health impacts of lead exposure.