Even Low Lead Exposure Linked To ADHD

The research findings support a growing body of national evidence suggesting there is no safe level of lead in the blood, said Joel Nigg, MSU professor of psychology and study director. Other studies show a link between low-level lead exposure and lower IQ.

Nigg said the mounting research spotlights the need for potentially tougher regulations on items that contain lead and other harmful elements that can get into the food supply or local environment of children – from cosmetics to cleaning supplies to electronic goods. Millions of Chinese-made toys have been recalled in the past year due to lead paint.

“We’ve got to re-examine the rules by which we release new materials into children’s environments, the way other countries like Canada and Sweden have begun to do,” Nigg said.

According to the study, which examined both children with and without ADHD, all 150 children had at least some lead in their blood, although none had levels higher than the 10 micrograms per deciliter level currently considered unsafe by the Centers for Disease Control and Prevention.

Children with ADHD had higher levels of lead in the blood than those without the disorder, according to the study, which was conducted with help from the Michigan Department of Community Health.

The neurotoxic effects of lead in the blood can interfere with stages of brain growth, such as synapse formation – a critical element in the development of appropriate self-regulatory control, according to Nigg’s 2006 book, “What Causes ADHD?” Children 2 and younger are especially vulnerable, he said.

While the “safe” level for lead in the blood was lowered from 25 mcg/dl to 10 mcg/ld in 1991, some scientists are now calling for the level to be dropped to 5 mcg/dl or even lower.

Nigg’s study is the first to examine such low blood levels in children diagnosed with ADHD under formal clinical criteria. Earlier studies used out-of-date criteria or children with much higher levels of blood lead. The average blood lead level of children with ADHD in the MSU study was less than 1.3 mcg/dl.

Bruce Lanphear is a physician and professor of pediatrics at Cincinnati Children’s Hospital Medical Center who also researches the effects of lead exposure in children. Lanphear, who was not involved in the MSU research, said, “This study, which is the first to examine the association of ADHD using strict diagnostic criteria, provides convincing evidence that low-level lead exposure is a risk factor of ADHD in children. Taken together with other research, this study provides sufficient evidence to increase our efforts to further reduce allowable levels in air, house dust, and water and consumer products.”

While the study didn’t examine where the lead exposure originated, Nigg speculates it came from lead dust in old houses and schools. Although lead paint was banned in 1978, many older housing units still contain some level of lead.

“No one can completely eliminate all dust and lead from those houses,” Nigg said. “If you’re a parent of an infant or toddler in an older home who is worried about this, your best advice is to become scrupulous about sweeping up dust and dirt, filter tap water, remove chipped paint and monitor what your children put in their mouths.”

Aging lead water pipes are also a potential source, according to the CDC. The Lansing Board of Water and Light is in the process of replacing thousands of lead water pipes in the city of Lansing. Many other U.S. cities also have replaced lead water pipes that were installed in the late 1800s and early 1900s.

The MSU study will continue for at least two more years and Nigg said he wants to triple the number of participants. To volunteer, parents of children ages 8-16 years with or without ADHD can call (517) 432-4894. Families receive a small payment and free screening for ADHD and learning problems.

His group’s latest research will appear in the Feb. 15 issue of Biological Psychiatry and is currently in the journal’s online edition. The study is funded by the National Institute of Mental Health and the MSU Office of the Vice President for Research and Graduate Studies.