Thousands of blood samples taken from children showed a connection to tobacco and lead. Those exposed to tobacco in the womb were 2½ times more likely to develop ADHD. Plus, kids with certain lead concentrations in their blood had four times the risk. Lead-based paint is still found in many homes built before 1978.
"When a toxin such as lead or tobacco enters the bloodstream and crosses the placenta, it interrupts that brain development and the consequences are lifelong. You can't rewind a child's brain development," said the study's author, Dr. Leonard Trasande with the Mt. Sinai School of Medicine.
The study stresses the importance of staying away from smoke and lead during pregnancy. Health experts fear they are not the only culprits, however. The experts said they believe people are exposed to countless pollutants and chemicals.
Trasande said many other toxins could be playing a role in neurological disorders like ADHD.
"There are some 80,000 chemicals in the environment, many of which are likely to impact brain development during the pre-natal period," he said.
Studies are now under way to find out which of those toxins may cause problems, but health experts said it may take a lot of time, money and patience.
In order to meet the criteria for having ADHD, a person must exhibit a certain number of symptoms in multiple settings and be impaired as a result of those symptoms.