Mothers who smoke during pregnancy are giving birth to babies with attention-deficit hyperactivity disorder (ADHD) more than double the rate compared to children from Moms who did not smoke. Children exposed to elevated lead levels as babies were also more than twice likely to be affected by ADHD. Combine the exposure of prenatal smoking and lead and the chances of having ADHD rose enormously. Children whose mothers smoked during pregnancy and whose blood showed signs of lead exposure had eight times the risk of having ADHD.

When you have both exposures, there is a synergistic effect," said study author Dr. Tanya Froehlich, a developmental and behavioral pediatric specialist and an assistant professor of pediatrics at Cincinnati Children’s Hospital Medical Center.

smoking-lead-pregnancy The research demonstrated that about 38 percent of ADHD cases among children aged 8 to 15 in the United States may be caused by prenatal exposure to tobacco smoke, while 25 percent of ADHD cases are due to lead exposure.

2,588 children aged 8 to 15 from around the nation participated in this 2001-2004 National Health and Nutrition Examination Survey conducted by the Centers for Disease Control and Prevention. Mothers were asked if they smoked during pregnancy to evaluate tobacco exposure, while lead concentrations were measured with a blood test. About 8.7 percent of these children met the criteria for ADHD, which is marked by inattentiveness, difficulty focusing, impulsivity and hyperactivity, according to the study.

ADHD was present in 28.6 percent of children who were exposed to both prenatal smoking and who had higher blood lead concentrations had, according to Dr. Froehlich.

Researchers did not find a strong link between exposure to secondhand cigarette smoke during childhood and ADHD.

Previous research has shown lead is toxic to children’s brains and is associated with lower IQs and hyperactivity in children.

"There is no such thing as a ‘safe’ level of lead," said Dr. Andrew Adesman, chief of developmental and behavioral pediatrics at Schneider Children’s Hospital in New Hyde Park, N.Y. “the lower the lead level, the better”.

Though much remains unknown about the specific causes of ADHD, "we have long believed ADHD is at least in large part due to abnormalities of dopamine in the brain," Dr. Adesman said, and past research revealed that lead exposure and cigarette smoking may alter the brain’s metabolism of dopamine.

"Lead is out there, and we need to take precautions, such as making sure we keep kids away from peeling paint and make sure they practice good hand washing before they eat if they are playing in the soil," Dr.Froehlich added. Children may also ingest lead from old water pipes, soil and toys. In the last few years there have been multiple recalls, some by major toy manufacturers such as Mattel and Fisher-Price, of products manufactured in China and Mexico that contained unsafe levels of lead. In addition, good nutrition, including making sure children have adequate levels of iron and calcium, can also protect from lead exposure. Children with iron and calcium deficiencies absorb more lead than children with better diets, Dr. Froehlich explained.