Cigarette smoke and lead are known to have bad effects on children. Some studies have shown a link to between the exposures and Attention Deficit Hyperactivity Disorder.

A new study shows those downsides begin as early as in the womb. Children exposed to cigarette smoke and to lead in utero were eight times more likely to be diagnosed with ADHD, according to an article appearing in today's Pediatrics.

For years, researchers have known too much lead exposure in pregnancy can lead to a host of developmental and behavioral problems once the child is born. And other research has shown a link between tobacco and attention problems. This study takes a look at both exposures to reveal a significant impact.

The team of researchers from around the country studied a national health survey of 2,588 children 8 to 15 years old. They measured lead levels in a child's blood and measured tobacco exposure based on how much smoking a woman reported during pregnancy. Children exposed to tobacco or lead alone were more likely to have ADHD. The risk was even greater when exposed to both toxins.

The findings may not be surprising -- we've known for years that lead exposure and smoking are bad during pregnancy. But consider that some 15 percent of women smoke during pregnancy, according to a 2004 study the article states. And nearly 2 percent of children nationwide have lead levels above what the CDC says are "levels of concern."

Understanding the causes of ADHD has been a challenge for researchers. They believe a mix of genes and environmental factors is at play. The authors say the new research could play an important role in tackling the condition.