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Age of greatest susceptibility to childhood lead exposure: a new statistical approach.

Hornung RW, Lanphear BP, Dietrich KN - Environ. Health Perspect. (2009)

Bottom Line: The ratio of BPb at 6 years to the BPb at 2 years showed a strong effect on IQ (p < .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.We conclude that 6-year BPb is more strongly associated with cognitive and behavioral development than is BPb measured in early childhood.

View Article: PubMed Central - PubMed

Affiliation: Cincinnati Children's Environmental Health Center, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio 45229-3039, USA. richard.hornung@cchmc.org

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 < .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.

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Related in: MedlinePlus

Annual BPb levels and 95% confidence intervals for Cincinnati and Rochester cohorts, individually and combined.
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f1-ehp-117-1309: Annual BPb levels and 95% confidence intervals for Cincinnati and Rochester cohorts, individually and combined.

Mentions: Of the 462 children in the Cincinnati and Rochester cohorts, complete data on BPb levels and covariates were available for 397 (86%) children. We found no significant mean differences for IQ scores or covariates between the 397 included children and the 65 children with one or more missing covariates. Characteristics of each cohort are similar, except for BPb levels and the proportion of nonwhite children (Table 1). The Cincinnati children had mean childhood average BPb concentrations that were approximately twice as high as those of the Rochester children (11.7 vs. 5.8 μg/dL) primarily because they enrolled 12–15 years earlier when lead exposures were more prevalent. The Cincinnati cohort also had a somewhat higher proportion of nonwhite children (89.1 vs. 71.0%). In each of the cohorts, as well as the combined data, the mean BPb levels were highest at 2 years of age (14.1 μg/dL, combined data) and lowest at 6 years of age (7.3 μg/dL) (Figure 1). Childhood average BPb from 6 months to 6 years of age in the combined cohorts was 9.9 μg/dL, with 58% of the children having childhood average BPb < 10 μg/dL. The mean of the ratio of 6-year to 2-year BPb concentrations was 0.58, with a range of 0.11–4.09. There were 25 children (6.3%) with a ratio > 1.0, meaning that the 6-year BPb was greater than the 2-year BPb. The average IQ for children at 6 years of age was 85.9.


Age of greatest susceptibility to childhood lead exposure: a new statistical approach.

Hornung RW, Lanphear BP, Dietrich KN - Environ. Health Perspect. (2009)

Annual BPb levels and 95% confidence intervals for Cincinnati and Rochester cohorts, individually and combined.
© Copyright Policy - public-domain
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2721877&req=5

f1-ehp-117-1309: Annual BPb levels and 95% confidence intervals for Cincinnati and Rochester cohorts, individually and combined.
Mentions: Of the 462 children in the Cincinnati and Rochester cohorts, complete data on BPb levels and covariates were available for 397 (86%) children. We found no significant mean differences for IQ scores or covariates between the 397 included children and the 65 children with one or more missing covariates. Characteristics of each cohort are similar, except for BPb levels and the proportion of nonwhite children (Table 1). The Cincinnati children had mean childhood average BPb concentrations that were approximately twice as high as those of the Rochester children (11.7 vs. 5.8 μg/dL) primarily because they enrolled 12–15 years earlier when lead exposures were more prevalent. The Cincinnati cohort also had a somewhat higher proportion of nonwhite children (89.1 vs. 71.0%). In each of the cohorts, as well as the combined data, the mean BPb levels were highest at 2 years of age (14.1 μg/dL, combined data) and lowest at 6 years of age (7.3 μg/dL) (Figure 1). Childhood average BPb from 6 months to 6 years of age in the combined cohorts was 9.9 μg/dL, with 58% of the children having childhood average BPb < 10 μg/dL. The mean of the ratio of 6-year to 2-year BPb concentrations was 0.58, with a range of 0.11–4.09. There were 25 children (6.3%) with a ratio > 1.0, meaning that the 6-year BPb was greater than the 2-year BPb. The average IQ for children at 6 years of age was 85.9.

Bottom Line: The ratio of BPb at 6 years to the BPb at 2 years showed a strong effect on IQ (p < .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.We conclude that 6-year BPb is more strongly associated with cognitive and behavioral development than is BPb measured in early childhood.

View Article: PubMed Central - PubMed

Affiliation: Cincinnati Children's Environmental Health Center, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio 45229-3039, USA. richard.hornung@cchmc.org

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 < .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.

Show MeSH
Related in: MedlinePlus