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1/3 ADHD Cases Linked to Lead, Smoking

Study Raises Questions About Acceptable Levels of Environmental Lead Exposure

WebMD Health News

Sept. 20, 2006 -- Nearly a third of ADHD cases may be due to two preventable causes: early childhood exposure to environmental lead and exposure to tobacco smoke in the womb.

"That's a whopping percentage," says Andrew Adesman, MD, chief of developmental and behavioral pediatrics at Schneider Children's Hospital in New Hyde Park, N.Y. Schneider was not associated with the study.

"This is further proof-positive that prenatal smoking has long-term developmental effects on kids, perhaps leading to an additional 270,000 cases of ADHD," Adesman tells WebMD. "Certainly the first take-home message is that pregnant women shouldn't smoke."

But the study's most innovative finding, Adesman tells WebMD, is that childhood exposure to lead, even at low levels that the government finds acceptable, also has detrimental effects on kids, perhaps leading to an additional 290,000 excess cases of ADHD.

2 Important Questions

This raises two important questions: Should the government lower its current threshold of an acceptable blood level, which is defined as higher than 10 micrograms per deciliter? And should public health agencies be more aggressive in eliminating lead from consumer products and taking steps to reduce high levels of lead found in homes and environments where young children play?

"What is suggested is that we as a society need to work harder to further eradicate potential sources of lead and be more vigilant about possible lead exposures in young children," Adesman says.

"Housing surveys estimate that 25 million American housing units contain one or more lead hazards," says researcher Bruce Lanphear, MD, director of the Cincinnati Children's Environmental Health Center at the Cincinnati Children's Hospital Medical Center.

"The most common source of lead exposure is from lead-based paint that disintegrates and contaminates house dust," Lanphear tells WebMD. Other sources include lead-glazed pottery and lead-containing cosmetics. Residences near highways may also have high levels of lead in air and dirt.

The study was published online Sept. 19 in the journal Environmental Health Perspectives.

ADHD Numbers May Be Even Higher

Lanphear and colleagues studied more than 4,700 children aged 4-15 and found that 4.2% were reported to have ADHD treated with medication. This finding is in line with national studies showing that 3% to 8% of U.S. children have ADHD.

The researchers also found that an additional 4% of the children had parent-reported ADHD but were not on medication. But they were not included in the researchers' analysis because parent reports are considered an imprecise measure of ADHD.

"Half of the children who were labeled as ADHD were excluded because they were never treated with medication," Adesman says. "That means that the estimated number of ADHD cases attributable to prenatal smoking and lead exposure may be even higher. I don't know that the numbers would necessarily be double, but they would be substantially higher."

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