Low blood lead levels associated with clinically diagnosed attention-deficit/hyperactivity disorder and mediated by weak cognitive control.

Full 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.

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Author information

First Name	LastName	Initials
Joel T	Nigg	JT
G Mark	Knottnerus	GM
Michelle M	Martel	MM
Molly	Nikolas	M
Kevin	Cavanagh	K
Wilfried	Karmaus	W
Marsha D	Rappley	MD

Affiliation: Department of Psychology, Michigan State University, East Lansing, Lansing, MI 48824-1116, USA. nigg@msu.edu

Grants: R21 MH 070542 (Agency:United States NIMH)

Journal and publication information

Publication Type: Journal Article; Research Support, N.I.H., Extramural; Research Support, Non-U.S. Gov't

Journal: Biological psychiatry (Biol Psychiatry).

Reference: 2008-Feb; vol 63 (issue 3) : pp 325-31

Language: eng

PMID: 17868654 (status: MEDLINE) (last retrieval date: 3/17/2008)

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MeSH headings (categories)

This article was linked to the MESH Headings shown below.

Adolescent
Attention Deficit Disorder with Hyperactivity - blood; complications
Child
Cognition Disorders - blood; etiology
Female
Humans

Humans
Intelligence - physiology
Lead - blood
Male
Mass Spectrometry - methods
Neuropsychological Tests

Associated Chemicals: Lead (7439-92-1)

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