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Jan. 22 2010 - 3:09 pm | 916 views | 0 recommendations | 5 comments

Is lead the culprit in ADHD?

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 hyperactivity 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 neurotoxin. 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/impulsivity 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 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.


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    Fascinating post. Both my kids fall into the 70% of ADHD kids who inherited the disorder–one is decidedly inattentive, while the other is an inattentive/hyperactive hybrid. Both are very bright and respond very positively to medication. Now, the next step is to take the stigma away from medicating this very real issue by making sure doctors are diagnosing this problem accurately and writing prescriptions only for those who really need it.

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    My daughter’s ADD is caused by gluten. It is hidden is processed foods under various names, i.e. food starch. She has Celiac Disease, an immune disorder. Scientists help to create this disorder by genetically engineering wheat to have more protein; in doing that they added more gluten. It is more than her body can tolerate; hense s new market for “gluten free” foods has been created. I’ll readily add that here may be additional causes for ADD, but this certainly is the cause for hers.

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    These are informative studies on a very critical topic. Thanks for getting this out there.

  4. collapse expand

    Here’s where the study of epigenetics can shed some light, possibly changing the 70/30 equation and bringing environmental causes to the forefront. The parents of ADHD children can sure use the potential guilt-moderation.

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    I've been a Washington, DC-based science writer for many years, specializing in psychology and human behavior. I currently write a blog for the Association for Psychological Science called "We're Only Human," and am also a regular contributor to Newsweek.com and Scientific American Mind. Crown will be publishing my book, On Second Thought: Outsmarting Your Mind's Hard-Wired Habits, in September. I am an old-school journalist embracing the world of new media. I'm on Facebook and Twitter. I believe that every news story--whether it's about money or politics or crime or love or health-- is in large part about psychology and the quirks of the human mind. When I am not writing, I am hanging out at Westside Club, riding my bicycle, listening to music and/or cooking for family and friends.

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    For more insights into the quirks of human nature, visit my “We’re Only Human” blog. Selections from the blog also appear regularly in the magazine Scientific American Mind and at the website Newsweek.com.