Current ADHD research suggests that around 70% may have a genetic origin but new studies by psychological scientist Joel Nigg of the Oregon Health & Science University suggest  that lead might play a significant role in the remaining 30%.

It has been known for a long time that lead is a neurotoxin but although the amount of lead in the environment has been dramatically reduced by the elimination of lead from  petrol and paint, it is still to be found in small amounts in everything from childrens’ jewellery to soil and drinking water.

Dr Nigg’s first study compared children formally diagnosed with ADHD to controls, and found that the children with hyperactivity/impulsivity symptoms had slightly higher levels of lead in their blood.
His second study showed a robust link between blood lead and both parent and teacher ratings of ADHD symptoms, including both hyperactivity and attention problems. In both studies, the connection was independent of IQ, family income, race, or maternal smoking during pregnancy.

Dr Nigg theorises that 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.

Joel Nigg. Attention-Deficit/Hyperactivity Disorder: Endophenotypes, Structure, and Etiological Pathways. Current Directions in Psychological Science, February, 2010

Courtesy of Science Daily

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