| Age of Greatest Susceptibility to Childhood Lead Exposure:
A New Statistical Approach Richard W. Hornung,1,2 Bruce P. Lanphear,1,2,3 and Kim N. Dietrich1,2 1Cincinnati Children’s Environmental Health Center, Cincinnati Children’s Hospital Medical Center, Cincinnati, Ohio, USA; 2Department of Environmental Health, University of Cincinnati College of Medicine, Cincinnati, Ohio, USA; 3Faculty of Health Sciences, Simon Fraser University and Child and Family Research Institute, British Columbia Children’s Hospital, Vancouver, British Columbia, Canada Abstract
Background: Susceptibility to lead toxicity is often assumed to be greatest during early childhood (e.g., 2 years of age) , but recent studies suggest that blood lead concentrations (BPb) taken at 5–7 years of age are more strongly associated with IQ. Objective: We aimed to determine the age of greatest susceptibility to lead exposure using an innovative statistical approach that avoids the problem of correlated serial BPb measurements. Methods: We analyzed two cohorts of children that were followed from infancy to 6 years of age in Rochester, New York (n = 211) , and Cincinnati, Ohio (n = 251) . Serial BPb levels were measured and IQ tests were done when children were 6 years of age. After adjustment for relevant covariates, the ratio of 6-year BPb to 2-year BPb was added to the multiple regression model to test whether the pattern of BPb profiles during childhood had additional effect on IQ. Results: The ratio of BPb at 6 years to the BPb at 2 years showed a strong effect on IQ (p < 0.001) when added to the multiple regression model that included the average childhood BPb. IQ decreased by 7.0 points for children whose BPb at 6 years of age was 50% greater than that at 2 years compared with children whose 6-year BPb was 50% less than their 2-year BPb. Similarly, criminal arrest rates were a factor of 3.35 higher for those subjects whose 6-year BPb was 50% higher than their 2-year BPb. Conclusions: We conclude that 6-year BPb is more strongly associated with cognitive and behavioral development than is BPb measured in early childhood. Key words: age effects, blood lead, collinearity, temporal pattern. Environ Health Perspect 117:1309–1312 (2009) . doi:10.1289/ehp.0800426 available via http://dx.doi.org/ [Online 7 May 2009]
Address correspondence to R.W. Hornung, Cincinnati Children’s Hospital Medical Center, 3333 Burnet Ave., MLC 7035, Cincinnati, OH 45229-3039 USA. Telephone: (513) 636-1948. Fax: (513) 636-4402. E-mail: richard.hornung@cchmc.org The authors declare they have no competing financial interests. Received 25 November 2008 ; accepted 7 May 2009.
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