Children exposed to secondhand smoke in the home appear to be at 50% higher risk of neurobehavioural disorders such as ADHD/ADD and learning disabilities compared to unexposed children according to an analysis led by the Harvard School of Public Health (HSPH) that was published in the journal Pediatrics this week. The analysts suggest if such a link were found to be causal, then secondhand smoke in the home is responsible for over quarter of a million children across the US developing ADHD and other neurobehavioural disorders.

For their research, Hillel Alpert, a research scientist for the Tobacco Control Research and Training Program at the HSPH in Boston, Massachusetts, and colleagues, examined data from the 2007 National Survey on Children’s Health. The telephone survey took place between April 2007 and July 2008.

The analysts were particularly interested in parent-reported information on secondhand smoke exposure in the home experienced by children from birth to the age of 12, and neurobehavioral disorders (that is, attention-deficit/hyperactivity disorder or ADHD/ADD, learning disabilities, and conduct disorders).

Using advanced statistical methods they looked for higher than expected neurobehavioral disorders and how these might be linked to exposure to secondhand smoke in the home. The tools they used allowed them to take into account potential confounders like socioeconomic background, income and so on.

The results showed that:

  • The nationally representative survey covered 55,358 American children under the age of 12.
  • 6% of these under 12s were exposed to secondhand smoke in the home: this corresponds to 4.8 million across the whole of the US.
  • The weighted prevalence of learning disabilities among these children was 8.2% (95% Confidence Interval CI ranged from 7.5 to 8.8%).
  • For ADHD/ADD this was 5.9% (95% CI: 5.5-6.4%) and for behavioral and conduct disorders this was 3.6% (95% CI: 3.1-4.0%).
  • Children exposed to secondhand smoke at home had a 50% higher chance (calculated as Odds Ratio) of having two or more childhood behavioral disorders compared with unexposed children.
  • Boys appeared to be at significantly higher risk than girls.
  • Older children, especially aged between 9 and 11, and those in the poorest households had the highest risk.
  • Expressed in absolute terms (that is looking at the equivalent across the whole of the US), if children had not been exposed to secondhand smoke in the home, and if the relationship between such exposure and risk were to be causal, then these figures would show it may be possible to prevent 274,000 children from developing neurobehavioral disorders.

Alpert and colleagues concluded that:

“The findings of the study, which are associational and not necessarily causal, underscore the health burden of childhood neurobehavioral disorders that may be attributable to SHS [secondhand smoke] exposure in homes in the United States.”

In January 2011, Alpert and colleagues reported that an increase in smoke-free homes across the US has led to a fall in childhood ear infections.

“Secondhand Smoke Exposure and Neurobehavioral Disorders Among Children in the United States.”
Zubair Kabir, Gregory N. Connolly, and Hillel R. Alpert
Pediatrics 2011; peds.2011-0023
Published ahead of print July 11, 2011, doi:10.1542/peds.2011-0023
Link to Abstract.

Written by: Catharine Paddock, PhD