| Blood Lead Concentrations < 10 µg/dL and Child Intelligence at 6 Years of Age Todd A. Jusko,1 Charles R. Henderson Jr.,2 Bruce P. Lanphear,3 Deborah A. Cory-Slechta,4 Patrick J. Parsons,5,6 and Richard L. Canfield7 1Department of Epidemiology, School of Public Health and Community Medicine, University of Washington, Seattle, Washington, USA; 2Department of Human Development, Cornell University, Ithaca, New York, USA; 3Cincinnati Children's Environmental Health Center, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio, USA; 4Department of Environmental Medicine, University of Rochester School of Medicine and Dentistry, Rochester, New York, USA; 5Trace Elements Laboratory, Wadsworth Center, New York State Department of Health, Albany, New York, USA; 6Department of Environmental Health Sciences, School of Public Health, The University at Albany, State University of New York, Albany, New York, USA; 7Division of Nutritional Sciences, Cornell University, Ithaca, New York, USA Abstract
Background: Few studies provide data directly relevant to the question of whether blood lead concentrations < 10 µg/dL adversely affect children's cognitive function. Objective: We examined the association between blood lead concentrations assessed throughout early childhood and children's IQ at 6 years of age. Methods: Children were followed from 6 months to 6 years of age, with determination of blood lead concentrations at 6, 12, 18, and 24 months, and 3, 4, 5, and 6 years of age. At 6 years of age, intelligence was assessed in 194 children using the Wechsler Preschool and Primary Scale of Intelligence–Revised. We used general linear and semiparametic models to estimate and test the association between blood lead concentration and IQ. Results: After adjustment for maternal IQ, HOME scale scores, and other potential confounding factors, lifetime average blood lead concentration (mean = 7.2 µg/dL ; median = 6.2 µg/dL) was inversely associated with Full-Scale IQ (p =0.006) and Performance IQ scores (p =0.002) . Compared with children who had lifetime average blood lead concentrations < 5 µg/dL, children with lifetime average concentrations between 5 and 9.9 µg/dL scored 4.9 points lower on Full-Scale IQ (91.3 vs. 86.4, p =0.03) . Nonlinear modeling of the peak blood lead concentration revealed an inverse association (p =0.003) between peak blood lead levels and Full-Scale IQ down to 2.1 µg/dL, the lowest observed peak blood lead concentration in our study. Conclusions: Evidence from this cohort indicates that children's intellectual functioning at 6 years of age is impaired by blood lead concentrations well below 10 µg/dL, the Centers for Disease Control and Prevention definition of an elevated blood lead level. Key words: cohort, electrothermal atomic absorption spectrometry, GAM, HOME, IQ, LOESS, Rochester, WPPSI-R. Environ Health Perspect 116:243–248 (2008) . doi:10.1289/ehp.10424 available via http://dx.doi.org/ [Online 20 November 2007]
Address correspondence to R.L. Canfield, Division of Nutritional Sciences, B-09 Savage Hall, Cornell University, Ithaca, NY 14853 USA. Telephone: (607) 255-9575. Fax: (607) 255-0178. E-mail: rlc5@cornell.edu We thank K. Alexander, K. DiBitetto, and K. Knauf for data collection ; K. Nason, S. Bender, and Y. Wang for data management ; and C. Cox and C. Karr, who provided valuable feedback on an earlier draft of this manuscript. This research was funded by National Institute of Environmental Health Sciences (NIEHS) grants R01ES008388 and T32ES007262. This work is solely the responsibility of the authors and does not necessarily represent the official views of the NIEHS, National Institutes of Health, or the New York State Department of Health. The authors declare they have no competing financial interests. Received 1 May 2007 ; accepted 3 November 2007.
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