A recent study reported in Environmental Health Perspectives suggests that about one-third of attention deficit cases among U.S. children may be linked with tobacco smoke before birth or to lead exposure afterward. Building 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's estimate is in line with a National Academy of Sciences report in 2000 that said about 3% 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.
ADHD is a brain disorder affecting between 4% and 12% 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. They asked whether mothers had smoked during pregnancy but used blood tests to determine lead exposure, said co-author Dr. Bruce Lanphear, a researcher at Cincinnati Children's Hospital Medical Center. Children whose mothers smoked during pregnancy were 2 1/2 times more likely to have ADHD than children who weren't prenatally exposed to tobacco.