Link Between Lead Exposure and ADHD Confirmed

The causal link between lead exposure and ADHD is real, a new study finds, adding to the negative effects caused by the once-abundant environmental toxin.

The study, published in Psychological Science, evaluated 386 healthy children between the ages of 6 and 17, half of whom had been formally diagnosed with ADHD. Researchers tested lead levels in the children’s blood; all were found to be in the “safe” range defined by the Centers for Disease Control and Prevention, and at a level consistent with other children in the U.S.

Some children, however, had a gene mutation known as HFE C282Y — a relatively common mutation found in 10 percent of the U.S. population. In those subjects with the gene, researchers found a causal link between lead exposure and severity of ADHD symptoms, particularly hyperactivity.

“Because the C282Y gene helps to control the effects of lead in the body and the mutation was spread randomly in the children, the findings of our study are difficult to explain unless lead is, in fact, part of the cause of ADHD, not just an association,” said Joel Nigg, Ph.D., the principal investigator on the study. Children without the HFE C282Y gene mutation also showed increased symptoms as lead exposure increased, but the causal link was not as strong.

The effects of lead were more pronounced in male children, which perhaps is related to the prevalence of hyperactive symptoms among boys with ADHD. These results are consistent with previous research linking neurodevelopmental conditions, gender, and severity of symptoms.

Lead in the environment has been greatly reduced over the last century, due primarily to government regulation and its removal from gasoline. However, lead is still found in some paints, children’s toys, and deteriorating water pipes. Low-level exposure over a lifetime can have negative health effects. At high levels, lead poisoning can lead to seizures, vomiting, memory loss, and even death; children under the age of 6 are particularly vulnerable to negative effects from lead.

The researchers emphasized that lead exposure is not the only cause of ADHD symptoms; rather, it’s one environmental factor that may lead to a formal ADHD diagnosis. Similarly, lead exposure doesn’t guarantee an ADHD diagnosis, but it may provide doctors with further clues about the root of a child’s symptoms.

“Our findings put scientists one step closer to understanding this complex disorder so that we may provide better clinical diagnoses and treatment options and, eventually, learn to prevent it,” said Nigg.

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