title: Low blood lead levels associated with clinically diagnosed attention-deficit/hyperactivity disorder and mediated by weak cognitive control.
abstract: BACKGROUND
  Attention-deficit/hyperactivity disorder (ADHD) and low-level lead exposure are high-prevalence conditions among children, and studies of large populations have suggested that these conditions are related. We examine this relationship in children from a community sample exposed to average background levels of lead who have a diagnosis of ADHD that is established by clinical criteria.
  
  
  METHODS
  One hundred fifty children ages 8-17 years participated (mean age = 14 years; 53 control subjects, 47 ADHD Predominantly Inattentive type, 50 ADHD-Combined type). Diagnosis was formally established with a semi-structured clinical interview and parent and teacher ratings. Children completed intelligence quotient (IQ) measures and the stop task (a neuropsychological measure). Lead was assayed from whole blood with inductively coupled plasma mass spectrometry.
  
  
  RESULTS
  Blood lead levels in this sample closely matched US population exposure averages, with a maximum level of 3.4 mug/dL. Blood lead levels were statistically significantly higher in ADHD-combined type than in non-ADHD control (p < .05) children. Blood lead was associated with symptoms of hyperactivity-impulsivity but not inattention-disorganization, after control of covariates. Blood lead levels were linked with a lower IQ (p < .05), but IQ did not account for effects on hyperactivity. Instead, hyperactivity mediated effects of lead on IQ. Effects of blood lead on hyperactivity-impulsivity were mediated by poor performance on the stop task. This mediation effect was independent of effects of lead on IQ.
  
  
  CONCLUSIONS
  Low-level lead exposure might be an important contributor to ADHD. Its effects seem to be mediated by less effective cognitive control, consistent with a route of influence via striatal-frontal neural circuits.
authors.affiliation: Department of Psychology, Michigan State University, East Lansing, Lansing, MI 48824-1116, USA. nigg@msu.edu
authors.forename: Joel T
authors.initials: JT
authors.lastname: Nigg
authors.forename: G Mark
authors.initials: GM
authors.lastname: Knottnerus
authors.forename: Michelle M
authors.initials: MM
authors.lastname: Martel
authors.forename: Molly
authors.initials: M
authors.lastname: Nikolas
authors.forename: Kevin
authors.initials: K
authors.lastname: Cavanagh
authors.forename: Wilfried
authors.initials: W
authors.lastname: Karmaus
authors.forename: Marsha D
authors.initials: MD
authors.lastname: Rappley
mesh_terms: D000293:Adolescent; D001289:Attention Deficit Disorder with Hyperactivity / Q000097:blood* / Q000150:complications*; D002648:Child; D003072:Cognition Disorders / Q000097:blood* / Q000209:etiology*; D005260:Female; D006801:Humans; D007360:Intelligence / Q000502:physiology; D007854:Lead / Q000097:blood*; D008297:Male; D013058:Mass Spectrometry / Q000379:methods; D009483:Neuropsychological Tests
chemical_list: D007854:Lead