Millions of U.S. children and adolescents could have deficits in reading and other skills caused by breathing secondhand smoke, researchers estimate. A new study links poor performance on several cognitive tests to tobacco-smoke exposure, even at low levels.
Past studies identified intellectual and behavioral problems in children of parents who smoked but didn’t determine the pervasiveness of exposure or the consequences of different degrees of exposure. Also, most previous research didn’t separate the effects of exposure in the womb from those of breathing tobacco smoke during childhood.
To fill these gaps, Kimberly Yolton of Cincinnati Children’s Hospital Medical Center and her colleagues sifted data from a large study of the U.S. kids’ health.
For 4,399 nonsmoking children and adolescents between 6 and 16, the researchers compared smoke exposure and performance on four cognitive tests. The team estimated exposure from measurements of blood concentrations of cotinine, a by-product of nicotine. The cognitive tests examined math skills, visual perception of spatial relationships, recognition of printed words, and short-term memory.
In 84 percent of the subjects, at least 0.05 nanogram of cotinine was detectable per milliliter of blood. Smokers’ blood generally contains more than 100 ng/ml cotinine, and 1 ng/ml is typical in children living with an adult smoker who consumes less than a pack of cigarettes per day, Yolton says.
In the study, children with 3 to 15 ng/ml cotinine, the category of greatest exposure, scored about 10 percent below the least-exposed group in reading, math, and spatial relations. However, smoke exposure didn’t appear to influence memory.
The findings suggest that more than 33.3 million U.S. children are at risk of at least minor mental deficits from secondhand smoke, the researchers estimate in the January Environmental Health Perspectives.
In isolating smoke’s effects, the researchers ruled out several known influences on children’s cognitive skills, including lead exposure, family income, and parental education. But other factors, such as alcohol and drug use by parents, could explain some differences reported in the study, says psychologist Barry Lester of Brown University in Providence, R.I.
Nevertheless, Lester says, even subtle neurological harm from smoke could tangibly affect some children. Cognitive problems related to secondhand smoke might result in some students requiring special education when they otherwise would have shown at least satisfactory performance in school, he says.