Blood lead → Cognitive performance

Mechanism

Lead can stand in for calcium at the synapse. Animal work shows damage to NMDA signaling, synapse formation, and myelination in developing cortex. The human papers do not isolate that pathway. They report a dose-response on named IQ tests. Canfield gave the Stanford-Binet at ages 3 and 5 to 172 Rochester children. Jusko gave the same cohort the WPPSI-R at age 6. Lanphear pooled Wechsler scales from seven prospective sites (Boston, Cincinnati, Cleveland, Mexico City, Port Pirie, Rochester, Yugoslavia) in 1,333 children followed from infancy to ages 5 to 10. Concurrent blood lead fit best. The log-linear model estimated a 6.9-point IQ decrement (95 percent CI 4.2 to 9.4) as concurrent lead rose from 2.4 to 30 µg/dL, and 3.9 points (2.4 to 5.3) from 2.4 to 10. The slope was steeper below 7.5 µg/dL than above it. Reuben gave the Dunedin cohort the WAIS-IV at age 38 and again at 45. Blood lead at age 11 (mean 10.99 µg/dL) tracked 1.61 IQ points lower at 38 per 5 µg/dL after maternal IQ, childhood IQ, and childhood SES were in the model (n=533). At 45 the WAIS-IV decrement was 2.07 points per 5 µg/dL (n=564). That is a midlife score on the same construct. SES and social mobility in the 2017 file are not this node. Taylor measured maternal blood lead at a median of 11 weeks in ALSPAC (mean 3.67 µg/dL) and gave the WPPSI at 4 (348 complete cases) and the WISC-III at 8 (1,823). After maternal education and family covariates, prenatal lead was not associated with child IQ. A sex-by-lead term at age 8 (p=0.033) does not identify. Child blood lead was available in a 235-child overlap and did not moderate. A prenatal null does not flip the childhood sign.

Caveats

The stamp is smoke because nobody randomized lead. The childhood association did not vanish after maternal IQ and home scores were in the model. That is the Canfield/Lanphear file. A new observational edge publishes as spurious and low. Paper count does not raise it. We do not put a robust-causal stamp on this pair without a dosing trial. That is a rule about design, not a claim that lead is harmless. Canfield and Jusko are one Rochester sample at two ages. Lanphear includes Rochester, so those children appear twice on this page. A 2019 erratum corrected Boston IQ and lead coding. The authors said the headline association held. The models adjust for maternal IQ, HOME scores, maternal education, and birth weight. Jusko also put family income and transferrin saturation in the model. Residual confounding remains. Housing quality, nutrition, and parental cognition still sit on the backdoor. Iron deficiency can raise lead absorption and can lower cognition on its own. The Rochester children were mostly low-income. Mean full-scale IQ in Jusko was 85. Do not export a child IQ association into a career or income arrow. Reuben 2017 is hung for the WAIS-IV at 38 and for IQ change from the WISC-R, not for NZSEI-06 or downward mobility. Reuben 2021 is hung for the WAIS-IV at 45, not for MRI. The two files are one Dunedin cohort at two ages. Taylor is maternal blood in pregnancy, not the child's venous lead. The adjusted prenatal association with IQ at 4 and 8 was null. That file does not raise the stamp and does not change the sign. Omitted: Wright 2021 (arrests), Lanphear 2008 (comment on pesticide confounding), Min 2022 (language and substance use), Kampouri 2024 (lead mixed with cadmium and fluoride), Searle 2015 (Port Pirie review; already in Lanphear). Beckley 2019 and Reuben 2020 stay off this pair. This page is a journal entry. It is not medical advice.

Effect

qualitative. Lanphear: 6.9 IQ points from concurrent 2.4 to 30 µg/dL. Canfield: 4.6 per 10 µg/dL. Reuben 2017: −1.61 IQ at 38 per 5 µg/dL. Sign is inverse. Design does not identify.

Nodes

Named confounders

• Educational attainment
• Disposable income
• Ferritin

Papers

• Intellectual impairment in children with blood lead concentrations below 10 microg per deciliter.

  RL Canfield, CR Henderson, DA Cory-Slechta, C Cox, TA Jusko, BP Lanphear · 2003 · The New England journal of medicine

• Low-level environmental lead exposure and children's intellectual function: an international pooled analysis.

  BP Lanphear, R Hornung, J Khoury, K Yolton, P Baghurst, DC Bellinger, RL Canfield, KN Dietrich · 2005 · Environmental health perspectives

• Blood lead concentrations < 10 microg/dL and child intelligence at 6 years of age.

  TA Jusko, CR Henderson, BP Lanphear, DA Cory-Slechta, PJ Parsons, RL Canfield · 2008 · Environmental health perspectives

• Association of Childhood Lead Exposure With MRI Measurements of Structural Brain Integrity in Midlife.

  A Reuben, ML Elliott, WC Abraham, J Broadbent, RM Houts, D Ireland, AR Knodt, R Poulton · 2021 · JAMA

• Association of Childhood Blood Lead Levels With Cognitive Function and Socioeconomic Status at Age 38 Years and With IQ Change and Socioeconomic Mobility Between Childhood and Adulthood.

  A Reuben, A Caspi, DW Belsky, J Broadbent, H Harrington, K Sugden, RM Houts, S Ramrakha · 2017 · JAMA

• Effects of low-level prenatal lead exposure on child IQ at 4 and 8 years in a UK birth cohort study.

  CM Taylor, K Kordas, J Golding, AM Emond · 2018 · Neurotoxicology