Can Secondhand Smoke Exposure Lower Children's IQ Levels?

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Can Secondhand Smoke Exposure Lower Children's IQ Levels?

Despite overwhelming evidence suggesting that environmental tobacco smoke (ETS, also known as secondhand smoke) may be detrimental to one's health, an estimated 40 percent of American children are subject to the effects of secondhand smoke in the home.

Among the pediatric conditions linked with secondhand smoke are middle ear disease, colic, and sudden infant syndrome, and a mélange of respiratory and behavioral problems. However, few studies have investigated what type of effect secondhand smoke can have on a child's cognitive abilities, or whether exposure to secondhand smoke as a child can have long-term effects on intelligence levels.

In this study, researchers analyzed data on 4,339 children ages 6 to 16, who had participated in the Third National Health and Nutrition Examination Survey. Instead of relying on interviews or questionnaires, however, the scientists measured levels of cotinine, a derivative of nicotine, in children's blood levels, and compared that information with the children's test scores on a series of math, reading and visuospatial exams. Results are presented as follows:

Serum cotinine levels were significantly higher among African American children than Hispanic children or non-Hispanic white children.

Children exposed to prenatal smoke and postnatal smoke, and children exposed to postnatal smoke alone, had higher cotinine levels than those exposed to prenatal smoke alone.

Mean cotinine levels were significantly higher among children who had at least one smoker living in the home. The level of cotinine increased as the number of smokers in the house increased and as the number of packs of cigarettes smoked per day in the house increased.

Children with the highest serum cotinine level received "significantly lower" performance scores on all four tests compared to children with the lowest cotinine level. Average math scores were 7.14 points lower in children with the highest concentrations of cotinine; reading scores were 7.54 points lower. Proportionally lower scores were also seen when evaluating block design and digit span tests.

Based on population estimates, the authors concluded that approximately 22 million American children are currently at risk of developing math and reading disorders that may be related to secondhand smoke. They added: "Exposure to ETS in U.S. children therefore has substantial public health impact beyond asthma, otitis media, and other widely recognized adverse consequences. In an accompanying article, the study's lead author suggested that the reduction in scores "is very roughly equivalent to the loss of two to five IQ points at varying levels of exposure."

Yolton K, Dietrich K, Auinger P, et al. Exposure to environmental tobacco smoke and cognitive abilities among U.S. children and adolescents. Environmental Health Perspectives January 2005;113(1):98-103.