ADHD Cases Linked to Lead, Smoke Exposure
One-third of attention deficit hyperactivity disorder cases are linked to prenatal exposures to cigarette smoke or childhood exposures to lead, researchers reported Monday.
The study, headed by researchers at Cincinnati Children’s Hospital Medical Center, was the first to estimate the number of ADHD cases attributable to environmental toxins.
The report “provides further evidence that we need to find ways to dramatically reduce prenatal tobacco smoke exposures and childhood lead exposures,” said principal author Dr. Bruce Lanphear.
ADHD is a condition marked by impulsivity, poor concentration and hyperactivity, making it difficult for children to pay attention in school. About 2 million children in the U.S. are treated for ADHD, according to government statistics.
Researchers analyzed data gathered on 4,704 children ages 4 to 15 as part of the federal National Health and Nutrition Examination Survey, which was conducted from 1999 to 2002.
About 8% of children in the study had been diagnosed with ADHD and 4.2% were prescribed drugs to treat the condition.
The study contained information on prenatal exposure to cigarette smoke and the concentration of lead in blood samples taken from the children.
The researchers, who published their findings in the journal Environmental Health Perspectives, linked blood lead concentrations of 2 micrograms per deciliter or greater to an increased risk of ADHD. Children in that group had an ADHD risk four times higher than children with the lowest blood lead levels -- under 0.8 micrograms per deciliter.
Federal standards consider blood lead levels below 10 micrograms per deciliter to be safe.
The study confirmed the link found in previous studies between prenatal exposure to cigarette smoke and ADHD. The latest study found that children exposed to tobacco smoke prenatally had an ADHD risk 2.5 times higher than unexposed children.
There was no connection between childhood exposure to tobacco smoke and ADHD.
Dr. David Feinberg, medical director of the Stewart and Lynda Resnick Neuropsychiatric Hospital at UCLA, said children exposed to high levels of lead were often hyperactive, so the link between lead and ADHD sounded reasonable.
But Feinberg said the estimates sounded too high. The study didn’t account for inherited genetic factors, which are one of biggest predictors of ADHD, Feinberg said.
“Was it the genes, the smoking, the lead or some combination?” Feinberg said. “It is not sorted out in the study.”
