Chicago – About one-third of attention-deficit cases among U.S. children may be linked with tobacco smoke before birth or to lead exposure afterward, according to provocative new research.
Even levels of lead the government considers acceptable appeared to increase a child’s risk of having attention deficit hyperactivity disorder, the study found.
It builds on previous research linking attention problems, including ADHD, with childhood lead exposure and smoking during pregnancy, and offers one of the first estimates for how much those environmental factors might contribute.
The study bolsters suspicions that low-level lead exposure previously linked to behavior problems “is in fact associated with ADHD,” said Dr. Leo Trasande, assistant director of the Center for Children’s Health and the Environment at Mount Sinai School of Medicine in New York, who was not involved in the research.
The study’s estimate is in line with a National Academy of Sciences report in 2000 that said about 3 percent of all developmental and neurological disorders in U.S. children are caused by toxic chemicals and other environmental factors and 25 percent are due to a combination of environmental factors and genetics.
The study was to be published online today in the journal Environmental Health Perspectives.
ADHD is a brain disorder affecting between 4 percent and 12 percent of school-age children – or as many as 3.8 million youngsters. Affected children often have trouble sitting still and paying attention and act impulsively at home and at school.
The researchers analyzed data on nearly 4,000 U.S. children ages 4 to 15 who were part of a 1999-2002 government health survey. Included were 135 children treated for ADHD.
Children whose mothers smoked during pregnancy were 2 1/2 times as likely to have ADHD as children who weren’t prenatally exposed to tobacco.
Children with blood lead levels of more than 2 micrograms per deciliter were four times as likely to have ADHD as children with levels below 0.8 micrograms per deciliter.
The government’s “acceptable” blood lead level is 10 micrograms per deciliter.
