If you need another reason to stop smoking while pregnant, or to rid your home of lead, a new study suggests that children whose mothers smoked during pregnancy and who are exposed to the metal have more than twice the usual risk of attention-deficit/hyperactivity disorder (ADHD).

Study co-author Dr. Tanya E. Froehlich, of Cincinnati Children’s Hospital Medical Center in Ohio, told Reuters Health that the lead finding is particularly “surprising,” given that the blood lead levels in the study children - even those in the top third of the sample - were, on average, about a tenth of the threshold for harmful effects set by the U.S. Centers for Disease Control and Prevention.

“These are not high levels of lead exposure; they are historically what we would consider to be low levels,” Froehlich said.

In a study of almost 2,600 children aged 8 to 15, Froehlich found that the rate of ADHD in the whole group was about 9 percent (222 children).

The rate of ADHD was about 17 percent in kids whose mothers smoked during pregnancy, and about 14 percent in kids who had blood lead levels in the top third. Almost 30 percent of kids who had both exposures had ADHD.

Although the study was not designed to prove that smoking and lead actually caused ADHD, the take home messages are still clear, Froehlich said: “Moms should make every effort to stop smoking before they become pregnant.”

It’s also important to stop smoking by others in the home, she said. In the current study, children in the top third of household smoke exposure had ADHD rates of more than 12 percent - again, higher than the background rate of about 9 percent.

Froehlich also advises parents to “take steps to reduce lead exposure, particularly from peeling lead paint present in older homes. And since lead can be in older pipes, don’t consume water that has been standing in the pipes; instead, let the water run for a bit before drawing it for drinking or cooking.”

Lead can also be found in soil where children play, so good hand-washing practices are essential, especially before eating. “And make sure they eat a diet high in iron and calcium because kids with poor diets and deficiencies in those areas will absorb more lead,” Froehlich said.

SOURCE: Pediatrics, December 2009.