title: Assessing windows of susceptibility to lead-induced cognitive deficits in Mexican children.
abstract: BACKGROUND
  The identification of susceptible periods to Pb-induced decrements in childhood cognitive abilities remains elusive.
  
  
  OBJECTIVE
  To draw inferences about windows of susceptibility using the pattern of associations between serial childhood blood lead (BPb) concentrations and children's cognitive abilities at 4 years of age among 1035 mother-child pairs enrolled in 4 prospective birth cohorts from Mexico City.
  
  
  METHODS
  Multiple longitudinally collected BPb measurements were obtained from children (1, 2, 3, and 4 years) between 1994 and 2007. Child cognitive abilities were assessed at 4 years using the general cognitive index (GCI) of the McCarthy Scales of Children's Abilities. We used multivariable linear regression to estimate the change in cognitive abilities at 4 years of age with a 10 μg/dL increase in childhood BPb concentrations adjusting for maternal IQ, education, marital status, child sex, breastfeeding duration, and cohort.
  
  
  RESULTS
  In separate models for each BPb measurement, 2 year BPb concentrations were most strongly associated with reduced GCI scores at 4 years after adjusting for confounders (β: -3.8; 95% confidence interval CI: -6.3, -1.4). Mutual adjustment for other BPb concentrations in a single model resulted in larger, but less precise estimate between 2 year BPb concentrations and GCI scores at 4 years of age (β: -7.1; 95% CI: -12, -2.0). The association between 2 year BPb and GCI was not heterogeneous (p=0.89), but some BPb and GCI associations varied in magnitude and direction across the cohorts. Additional adjustment for child hemoglobin, birth weight, gestational age, gestational BPb concentrations, or test examiner did not change the pattern of associations.
  
  
  CONCLUSIONS
  Higher BPb concentrations at 2 years of age were most predictive of decreased cognitive abilities among these Mexico City children; however, the observed pattern may be due to exposure, outcome, or cohort related factors. These results may help developing countries more efficiently implement childhood Pb prevention strategies.
authors.affiliation: Department of Environmental Health, Harvard School of Public Health, Boston, MA, USA. jbraun@hsph.harvard.edu
authors.forename: Joe M
authors.initials: JM
authors.lastname: Braun
authors.forename: Elaine
authors.initials: E
authors.lastname: Hoffman
authors.forename: Joel
authors.initials: J
authors.lastname: Schwartz
authors.forename: Brisa
authors.initials: B
authors.lastname: Sanchez
authors.forename: Lourdes
authors.initials: L
authors.lastname: Schnaas
authors.forename: Adriana
authors.initials: A
authors.lastname: Mercado-Garcia
authors.forename: Maritsa
authors.initials: M
authors.lastname: Solano-Gonzalez
authors.forename: David C
authors.initials: DC
authors.lastname: Bellinger
authors.forename: Bruce P
authors.initials: BP
authors.lastname: Lanphear
authors.forename: Howard
authors.initials: H
authors.lastname: Hu
authors.forename: Martha M
authors.initials: MM
authors.lastname: Tellez-Rojo
authors.forename: Robert O
authors.initials: RO
authors.lastname: Wright
authors.forename: Mauricio
authors.initials: M
authors.lastname: Hernandez-Avila
mesh_terms: D000328:Adult; D002675:Child, Preschool; D003072:Cognition Disorders / Q000097:blood / Q000139:chemically induced* / Q000453:epidemiology*; D015331:Cohort Studies; D002658:Developmental Disabilities / Q000139:chemically induced* / Q000453:epidemiology; D004198:Disease Susceptibility; D005260:Female; D006801:Humans; D007223:Infant; D007854:Lead / Q000097:blood; D007855:Lead Poisoning / Q000150:complications* / Q000453:epidemiology*; D016014:Linear Models; D008297:Male; D008800:Mexico / Q000453:epidemiology; D009034:Mother-Child Relations; D009483:Neuropsychological Tests; D011237:Predictive Value of Tests; D012189:Retrospective Studies; D055815:Young Adult
chemical_list: D007854:Lead