Study says lead may be the culprit in ADHD

January 28, 2010, Association for Psychological Science

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 despite nearly a century of study, the disorder's roots remain mysterious.

Much of modern ADHD research has focused on heritability of the condition, and indeed evidence suggests that genes may account for as much as 70 percent of and inattention in children. But that leaves 30 percent unexplained, so 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 an old villain—lead—and what's more it explains the causal pathway from exposure to disability.

Lead is a . This has been known for a long time, and in fact government regulation drastically reduced environmental lead a generation ago. But regulating automobile fuel and paint didn't entirely eliminate lead from the environment. It's found in trace amounts in everything from children's costume jewelry to imported candies to soil and drinking water. Every American today is exposed to low levels of the metal, and indeed 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 quite recently, but two recent studies now provide strong evidence. The first study compared children formally 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/ symptoms, not inattention. But a 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.

Nigg offers a causal model for the disabling symptoms associated with : 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.

Related Stories

Recommended for you

Engaging in physical activity decreases people's chance of developing depression

April 24, 2018
An international team including researchers from King's College London have found physical activity can protect against the emergence of depression, regardless of age and geographical region.

Early childhood interventions show mixed results on child development

April 24, 2018
Early childhood interventions may have some efficacy in boosting measures of child health and development in low income countries, but more work is needed to sort out how to implement these interventions, according to a new ...

People expect their memory to fade as early as their 50s

April 24, 2018
People across the UK expect their memory to worsen in their 50s, according to new research from Heriot-Watt University.

Imagining a positive outcome biases subsequent memories

April 24, 2018
Imagining that a future event will go well may lead you to remember it more positively after it's over, according to findings from research published in Psychological Science, a journal of the Association for Psychological ...

Depressed, inactive and out of work—study reveals lives of lonely young adults

April 24, 2018
New research from King's College London shows that lonely young adults are more likely to experience mental health problems and more likely to be out of work than their peers. The study, published today in Psychological Medicine, ...

Sense of control and meaning helps protect women from anxiety

April 24, 2018
People who feel in control of their lives and who find purpose and meaning in life are less likely to have anxiety disorders even when going through the toughest times, according to a study led by the University of Cambridge.

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.