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Could lead affect ADHD?

By Staff
I found the following article written by one of my colleagues, Laura Booth who is an Environmental Health and Homes Specialist, very thought provoking and decided to share it with you today. It’s one of those article that makes you say, “Hmmm… that’s rather interesting.”
ADHD, or attention-deficit/hyperactivity disorder, is among the costliest of behavioral disorders. Its combination of inattention,impulsivity and hyperactivity leads to accidental injuries, school failure, substance abuse, antisocial behavior and more. Yet despitenearly a century of study, the disorder’s roots remain mysterious.
Much of modern ADHD research has focused on heritability of the condition, and evidence suggests that genes may account for as much as 70 percent of hyperactivity and inattention in children. That leaves 30 percent unexplained.
Recently, the focus has shifted to the environment. What is it that triggers an underlying susceptibility and changes it into a full-blown disorder? New research suggests that the culprit may be lead. It explains the causal pathway from exposure to disability.
Lead is a neurotoxin. Although government regulation drastically reduced environmental lead a generation ago, regulating automobile fuel and paint didn’t entirely eliminate lead from the environment. It is found in trace amounts in everything from children’s costume jewelry to imported candies to soil and drinking water.
Today, every American is exposed to low levels of the metal and nearly all children have measureable levels of lead in their bodies. According to psychological scientist Joel Nigg of the Oregon Health & Science University, this universal low-level exposure makes lead an ideal candidate for the disorder’s trigger.
This was just a theory until two recent studies provided strong evidence. The first study compared children diagnosed with ADHD to controls, and found that the children with the disorder had slightly higher levels of lead in their blood. This study showed a link only between blood lead and hyperactivity/impulsivity symptoms, not inattention.
The second study showed a link between blood lead and ADHD symptoms, including hyperactivity and attention problems. In both studies, the connection was independent of IQ, family income, race or maternal smoking during pregnancy.
Nigg offers a causal model for the disabling symptoms associated with ADHD: Lead attaches to sites in the brain’s striatum and frontal cortex, where it acts on the genes in these regions-causing them to turn on or remain inactive. Gene activity shapes the development and activity of these brain regions. By disrupting brain activity, the toxin in turn alters psychological processes supported by these neurons, notably cognitive control. Finally, diminished cognitive control contributes to hyperactivity and lack of vigilance. Nigg describes his new data and his explanatory model in the February issue of the journal “Current Directions in Psychological Science.”
For more information on this study, contact Joel Nigg at niggj@ohsu.edu.