Low Lead Levels Linked to Attention Deficit Disorder

The study examined children with and without attention deficit hyperactivity disorder, ADHD, and found that all 150 children had at least some lead in their blood.

None had levels higher than the 10 micrograms per deciliter (mcg/dl) level currently considered unsafe by the federal 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 research findings support a growing body of national evidence indicating there is no safe level of lead in the blood, said study director Joel Nigg, MSU professor of psychology.

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 Earlier studies used out-of-date criteria or children with much higher levels of blood lead.

Child in close contact with lead-based paint in an older building. (Photo courtesy Marin County)

The average blood lead level of children with ADHD in the Michigan State study was less than 1.3 mcg/dl.

Nigg said the findings demonstrate the need for 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.

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 aged two 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 five mcg/dl or even lower.

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," said Lanphear.

While the study did not examine where the lead exposure originated, Nigg speculates it came from lead dust in old houses and schools. Although lead paint was banned in the United States in 1978, many older housing units still contain some level of lead. More than 80 percent of homes built before 1978 contain lead paint, according to the U.S. Environmental Protection Agency, EPA.

"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.

The study is funded by the National Institute of Mental Health and the MSU Office of the Vice President for Research and Graduate Studies. The findings will appear in the February 15 issue of Biological Psychiatry and are currently in the journal's online edition.

Lead poisoning is a top environmental health hazard for young children, affecting as many as 1.7 million children age five and under, according to the Centers for Disease Control and Prevention.

Even at low levels, lead poisoning in children can cause IQ deficiencies, reading and learning disabilities, impaired hearing, reduced attention spans and other behavior problems. Pregnant women poisoned by lead can transfer lead to a developing fetus, resulting in adverse developmental effects.

The only way to know if your child is being lead poisoned is to get a blood test, the EPA advises, saying, "If your child is at risk, have a blood test done as early as six months. The intellectual and behavioral damage done to children can be prevented, but, once done, cannot be reversed."

Copyright Environment News Service (ENS) 2007. All rights reserved.