title: Late effects of low blood lead concentrations in children on school performance and cognitive functions.
abstract: BACKGROUND
  Although it is known that lead is a neurotoxin that negatively impacts cognitive functions at low blood concentrations (B-Pb), little is known about the impact of early exposure on later cognitive functions.
  
  
  OBJECTIVE
  This study assesses the effects of very low lead exposure in early childhood on teenage cognitive performance.
  
  
  METHODS
  Using data collected between 1978 and 2007, we analyzed B-Pb (median 30 μg/L; six-fold decrease over time) in 3176 Swedish children (age 7-12). School performance in grade 9 (age 16; boys and girls) and over-all IQs measured during conscription examinations (age 18-19; mainly boys) were obtained from registers. In multivariate models, potential confounders (age at blood sampling, sex, parents' education, family economy, and country of birth of child and parents) and effect modifiers (socioeconomic; father's IQ at conscription examination) were included.
  
  
  RESULTS
  There were statistically significant adjusted negative associations between school performance (Grades up to 1991: P<0.0001; Merits 1992-2007:P<0.0001) and IQ (P=0.03) and B-Pb. The dose-response relationships were non-linear. Effects were more pronounced for B-Pb≤50 μg/L than for higher levels. In the B-Pb range 5-50 μg/L, the average IQ loss corresponded to about 5 IU. There was no significant effect modification associated with socioeconomic factors.
  
  
  CONCLUSIONS
  Lead causes neurotoxic effects at very low exposures (B-Pb<50 μg/L) in childhood and these effects remain for many years.
authors.affiliation: Division of Occupational and Environmental Medicine, University Hospital, SE-221 85 Lund, Sweden. Electronic address: Staffan.Skerfving@med.lu.se.
authors.forename: Staffan
authors.initials: S
authors.lastname: Skerfving
authors.affiliation: Division of Occupational and Environmental Medicine, University Hospital, SE-221 85 Lund, Sweden.
authors.forename: Lina
authors.initials: L
authors.lastname: Löfmark
authors.affiliation: Division of Occupational and Environmental Medicine, University Hospital, SE-221 85 Lund, Sweden.
authors.forename: Thomas
authors.initials: T
authors.lastname: Lundh
authors.affiliation: Division of Occupational and Environmental Medicine, University Hospital, SE-221 85 Lund, Sweden.
authors.forename: Zoli
authors.initials: Z
authors.lastname: Mikoczy
authors.affiliation: Division of Occupational and Environmental Medicine, University Hospital, SE-221 85 Lund, Sweden.
authors.forename: Ulf
authors.initials: U
authors.lastname: Strömberg
mesh_terms: D000293:Adolescent; D002648:Child; D003071:Cognition / Q000502:physiology*; D004522:Educational Status; D004781:Environmental Exposure; D005260:Female; D006801:Humans; D007360:Intelligence; D007854:Lead / Q000032:analysis / Q000097:blood*; D008297:Male; D012044:Regression Analysis; D012189:Retrospective Studies; D013054:Spectrophotometry, Atomic; D011795:Surveys and Questionnaires; D013548:Sweden; D055815:Young Adult
chemical_list: D007854:Lead
keywords: Blood; Dose–response; IQ; Lead; School performance