Could smoking and lead be related to ADHD?


ADHD, or Attention Deficit/Hyperactivity Disorder, is one of the most common childhood conditions in the class of neurobehavioral diseases. (Neuro- referring to the brain, and behavioural referring to the hallmark symptoms of ADHD, which include inattention, hyperactivity and poor impulse control.)

As many as 60 percents of kids with ADHD will have features of the disorder persisting into adulthood. Under the age of 18, as many as 8 to 10 percents of boys and 3 to 4 percent of females have the condition.

There are a lot of myths that surround ADHD, including that it is caused by poor parenting or sugar or preservatives. In fact, this disease is related to the brain’s chemistry. There is evidence that heredity may play some role as well. Research has shown that if a parent has ADHD, there is a 57 percent chance their child will as well. And if one child has ADHD, about 1/3 of their siblings will have it as well.


However, research has shown a link with some environmental exposures that can be linked to ADHD. A new study released this week in the journal Pediatrics looked at exposure to two known toxins that have been linked to ADHD. The first is prenatal exposure to smoke and the second is blood levels of lead.

Several thousand children, representative of the U.S. population, between the ages of 8 to 15 were examined for the study. A total of 8.6% meeting the diagnostic criteria for ADHD.

The results showed that children who were exposed to tobacco prenatally were more than twice as likely to develop ADHD.

Those with lead levels in the highest tertile compared to those in the lowest had a 2.3-fold increased likelihood of having the diagnosis.

What was most startling was that if the children had a joint exposure, the increased risk was far greater than the two risks added together, for a marked likelihood of having the diagnosis at 8.1 times those without the exposures.

We know that both tobacco and lead can have a great impact on brain chemical systems called dopamine. It is impossible to prove that one’s exposure causes the outcome. However, the association is quite strong.

Some have suggested that there might be some unknown and unmeasured genetic component that is also associated with the mother’s desire to smoke.

ADHD is typically treated with medication and behavioural therapy, however, this intriguing study suggests that as many as 35 percents of ADHD cases in children could be reduced by eliminating both these environmental exposures.

It is clear that from a prevention point of view, limiting these two exposures can be a relatively easy way to decrease ADHD. Given that up to 15% of women smoke during pregnancy, it is clear that we need better counselling and awareness to get women to stop smoking during pregnancy.