Tobacco Smoke, Lead & ADHD

The November issue of the medical journal Pediatrics published research from Dr. Robert Kahn et al regarding the relationship between tobacco smoke, lead concentrations, and ADHD.

Kahn, a physician and researcher at Cincinnati Children’s Hospital Medical Center, Ohio, found that two risk factors: 1) exposure to tobacco in the womb and 2) exposure to lead in childhood significantly increased the likelihood of ADHD developing  in children.

The researchers used data from the National Health and Nutrition Examination Survey. Tobacco exposure in the womb was measured by reports of cigarette use during pregnancy, and childhood lead exposure was assessed by blood levels. Of the 2588 cases they reviewed, the researchers determined that children aged 8 – 15 who were exposed to tobacco smoke in the womb were 2.4 times more likely to have ADHD. Children with lead blood levels in the top third of the population had a 2.3-fold increased likelihood of ADHD diagnosis.

Lead researcher, Tanya E. Froehlich, MD, cited that the combination from both lead and tobacco smoke created a synergistic effect, an even greater effect than smoke or lead alone. Children who were exposed to  both tobacco smoke in the womb and higher lead levels had a more than eightfold increased chance of having ADHD compared to children who weren’t exposed to either.

The study does have limitations; the researchers analyzed data on smoking that was derived from the mothers’ answers on a questionnaire. The data did not include the number of cigarettes smoked. And while the researchers found a link between tobacco, lead and ADHD, they did not prove that these factors actually caused the disorder. This is similar to previously published research on prenatal tobacco smoke and lead levels.

Curiously, smoking tobacco is twice as popular in the adult ADHD population compared to the non-ADHD adult population.  Columbia University researchers established a study to determine if smoking ameliorated ADHD symptoms in adults back in 2006.  If tobacco smoke truly increases the risk of developing ADHD, the popularity of smoking among ADHD adults may create a cycle of producing more ADHD children if smoking is done prenatally.

While a strong genetic link is still the likely cause of ADHD, environment still plays a significant role in brain development. The researchers assert that perhaps up to 35 per cent of cases of ADHD in youngsters aged between 8 and 15 could be reduced by getting rid of both prenatal exposure to tobacco and childhood exposure to lead.