Boys with asthma who are exposed to higher levels of tobacco smoke at home are more likely to have behavioral problems, new research shows.

“These findings should encourage us to make stronger efforts to prevent childhood exposure to tobacco smoke, especially among higher risk populations, such as children with asthma,” Dr. Kimberly Yolton of the Cincinnati Children’s Hospital Medical Center in Ohio said in a press release accompanying the study.

While the detrimental effects of tobacco smoke exposure on children’s health and cognition are well known, there has been less research into how this exposure might affect behavior, Yolton and her team point out in the Journal of Developmental and Behavioral Pediatrics. The studies that have looked at the issue have used parent reports to gauge children’s exposure, which may not be accurate, they add.

To get a clearer idea of this relationship, the researchers evaluated 220 boys and girls with asthma participating in a trial investigating the effects of air filters on their symptoms, lung function, and health care use. All of the children underwent blood tests to measure their levels of the nicotine byproduct cotinine at the study’s outset, which is considered to be the best way to measure tobacco smoke exposure.

Girls’ cotinine levels indicated that they were breathing more second-hand smoke than boys. While there was no link between cotinine levels and behavior in girls, the researches did find an association with boys.

Specifically, the greater the boys’ exposure, the more likely they were to have externalizing behavior problems such as hyperactivity, aggression and conduct disorders. They were also more likely to have internalizing behaviors, for example symptoms of anxiety and depression.

While past research has linked tobacco smoke exposure to externalizing behavior in children, the researchers note, children with asthma tend to have internalizing behavior problems.

The findings can’t be generalized to children who don’t have asthma, they add, but they do “provide further evidence that even low levels of environmental smoke may contribute to behavior problems in children.”

SOURCE: Journal of Development and Behavioral Pediatrics, online December 4, 2008.