Low-level environmental lead exposure and children's intellectual function: an international pooled analysis.
Lead is a confirmed neurotoxin, but questions remain about lead-associated intellectual deficits at blood lead levels < 10 microg/dL and whether lower exposures are, for a given change in exposure, associated with greater deficits. The objective of this study was to examine the association of intelligence test scores and blood lead concentration, especially for children who had maximal measured blood lead levels < 10 microg/dL. We examined data collected from 1,333 children who participated in seven international population-based longitudinal cohort studies, followed from birth or infancy until 5-10 years of age. The full-scale IQ score was the primary outcome measure. The geometric mean blood lead concentration of the children peaked at 17.8 microg/dL and declined to 9.4 microg/dL by 5-7 years of age; 244 (18%) children had a maximal blood lead concentration < 10 microg/dL, and 103 (8%) had a maximal blood lead concentration < 7.5 microg/dL. After adjustment for covariates, we found an inverse relationship between blood lead concentration and IQ score. Using a log-linear model, we found a 6.9 IQ point decrement [95% confidence interval (CI), 4.2-9.4] associated with an increase in concurrent blood lead levels from 2.4 to 30 microg/dL. The estimated IQ point decrements associated with an increase in blood lead from 2.4 to 10 microg/dL, 10 to 20 microg/dL, and 20 to 30 microg/dL were 3.9 (95% CI, 2.4-5.3), 1.9 (95% CI, 1.2-2.6), and 1.1 (95% CI, 0.7-1.5), respectively. For a given increase in blood lead, the lead-associated intellectual decrement for children with a maximal blood lead level < 7.5 microg/dL was significantly greater than that observed for those with a maximal blood lead level > or = 7.5 microg/dL (p = 0.015). We conclude that environmental lead exposure in children who have maximal blood lead levels < 7.5 microg/dL is associated with intellectual deficits.
Lanphear
Bruce P
BP
Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio 45229-3039, USA. bruce.lamphear@cchmc.org
Hornung
Richard
R
Khoury
Jane
J
Yolton
Kimberly
K
Baghurst
Peter
P
Bellinger
David C
DC
Canfield
Richard L
RL
Dietrich
Kim N
KN
Bornschein
Robert
R
Greene
Tom
T
Rothenberg
Stephen J
SJ
Needleman
Herbert L
HL
Schnaas
Lourdes
L
Wasserman
Gail
G
Graziano
Joseph
J
Roberts
Russell
R
D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D004781:Environmental Exposure; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D007360:Intelligence / Q000187:drug effects*; D007361:Intelligence Tests; D007854:Lead / Q000097:blood* / Q000633:toxicity*; D008137:Longitudinal Studies; D008297:Male
D007854:Lead